CA1336530C - Human serum albumin crystals and method of preparation - Google Patents
Human serum albumin crystals and method of preparationInfo
- Publication number
- CA1336530C CA1336530C CA000575341A CA575341A CA1336530C CA 1336530 C CA1336530 C CA 1336530C CA 000575341 A CA000575341 A CA 000575341A CA 575341 A CA575341 A CA 575341A CA 1336530 C CA1336530 C CA 1336530C
- Authority
- CA
- Canada
- Prior art keywords
- solution
- serum albumin
- human serum
- crystals
- crystal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07K—PEPTIDES
- C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
- C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
- C07K14/76—Albumins
- C07K14/765—Serum albumin, e.g. HSA
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/54—Organic compounds
- C30B29/58—Macromolecular compounds
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/30—Self-sustaining carbon mass or layer with impregnant or other layer
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31536—Including interfacial reaction product of adjacent layers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31725—Of polyamide
- Y10T428/31768—Natural source-type polyamide [e.g., casein, gelatin, etc.]
Abstract
HSA crystals are provided in the form of tetragonal plates having the space groups P4212, the crystals being grown to sizes in excess of 0.5 mm in two dimensions and a thickness of 0.1 mm. Growth of the crystals is carried out by hanging drop method wherein a precipitant solution containing PEG and a phosphate buffer is mixed with an HSA solution, and a droplet of mixed solution is suspended over a well of precipitant solution.
Crystals grow to the desired size in 3 to 7 days. Concen-tration of reagents, pH and other parameters are con-trolled within prescribed limits. The resulting crystals exhibit a size and quality such as to allow performance of x-ray diffraction studies and enable the conduct of drug binding studies as well as genetic engineering studies.
Crystals grow to the desired size in 3 to 7 days. Concen-tration of reagents, pH and other parameters are con-trolled within prescribed limits. The resulting crystals exhibit a size and quality such as to allow performance of x-ray diffraction studies and enable the conduct of drug binding studies as well as genetic engineering studies.
Description
-- HU2~ 3BRUM ALBUMIN CRY8TAL8 -AND I~ETHOD OF PREPAR~TION
Technical Field This invention relates to protein crystal growth and more particularly to the preparation of crystals of human serum albumin in a form and size suitable for x-ray studies of crystal structure.
Background of the Invention Serum albumin, a protein of multiple functions and manifold applications, is one of the most extensively studied proteins in biochemistry. Over 25,000 literature citations involving the biochemistry and/or applications of serum albumins have been published since 1969. The mammalian serum albumins proteins are known to be the product of three tandem gene duplications, and possess high helical content (60%) and high cysteine content (17 disulphides) with approximate molecular weights in the range of 65,000 daltons. Complete amino acid sequences are known for bovine, rat, and human serum albumins.
Although the principal function of serum albumin remains unknown, it contributes to many transport and regulatory processes. Many studies have focused on the multifunctio-nal binding properties of this interesting protein which range from various metals, e.g., Ca and Cu, to fatty acids, hormones, and a wide spectrum of therapeutic drugs.
The majority of these binding studies have involved the human serum albumin (HSA) and many have shown that the distribution, free concentration, and metabolism of various pharmaceuticals can be significantly altered as a function of the magnitude of binding to HSA.
A detailed knowledge of the three-dimensional structure of serum albumin is imperative in order to fully understand the binding modes as well as many of the physical properties of this multifaceted protein. In addition, since many newly developed pharmaceuticals are rendered less effective by HSA; it is apparent that the crystal structure of a serum albumin, particularly the human form, will find very broad and significant applica-tion in the area of rational drug design. Consequently, the serum albumins have been the subject of ongoing crystallographic investigation which includes the documen-tation of several crystal forms (Table 1). Because of difficulties with crystal size, quality, and/or reproduci-bility, the three-dimensional structure of a serum albumin remains unknown.
This invention is concerned with the methodology required to produce a new crystal form of HSA which can be grown reproducibly as large, relatively high quality crystals suitable for x-ray structure determination. Once the three dimensional structure has been determined it will become possible to learn the molecular details involved in the binding of the albumin with a large number of pharmaceutical compounds. This may be done by soaking crystals in an appropriate stabilizing solution which contains the drug molecules of interest. If the binding sites are available in this crystal form, a crystalline array containing the serum albumin protein and the drug molecule will be produced. Details of the molecular interaction between the drug and protein can then be determined by established procedures in x-ray crystallog-raphy.
Due to the multiple binding capabilities of HSA, knowledge of its three dimensional structure combined with suitable crystals, may also provide assistance in deter-mining the structures of various small molecules and perhaps small proteins which have proven difficult to crystallize.
Crystals of human serum albumin have been known for some time. As early as 1952, large crystals of HSA
had been grown. Detailed x-ray examination of these and other reported crystal forms, including crystals of Horse serum albumin were published by McClure and Craven in 1974 (1) See Table 1, below. Crystals of HSA have also been grown by Rao and co-workers (2). Table 1 summarizes the crystallographic data published to date on several human serum albumin crystal forms. According to Peters in a recent review (1985) on serum albumins (3):
Although readily crystallized, albumin has relinquished few of its secrets through x-ray crystallography to date.
...Structural information from these crystals is awaited eagerly, but obtaining it appears to be fraught with obstacles.
Low described monoclinic crystals as soft waxy, and crystals studied by Rao, et al.
(1976) have tended to dissolve under study.
;~,.......................................................................... .
g V
0 0 ~ ~
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lU U~ ~o r~
O ~ O~
~ _ _ ~-- O --Ul C U~--N 8 m 5~ N _ 0 _ ~"
NU U U U~ ~_ 0~ o~ O C
C~C ~ O _ 1~1 ~ N U
.._ ._ ~ . o . j~.C
E _ L.u N ~ ~ N U~ ~< -- ~ _ 9- .C ~U ~ ~} C 4, o U U U U
~1-- U~ ~ O m 0 _ a V I ~ ~ CO
-c : <
a _ ~ _ . ~ a .. O
c . c o .. - ._ o 2 ~ o ~ ~ . Cl ~ : I ~ I 1' I _N~
~:.
~ ,.
Crystals of the monoclinic form reported by McClure and Craven appear to be the highest quality;
unfortunately, the crystals are small and difficult to reproduce. It is difficult to adequately compare the crystal quality of the remaining tetragonal crystal form with the tetragonal crystal form reported here, since the diffraction resolution reported for that crystal form was obtained with a conventional sealed tube source.
It is therefore an object of this invention to provide HSA in the form of crystals amenable to use in x-ray diffraction studies.
Another object is to provide HSA crystals having a size of at least 0.5mm in two dimensions.
Yet another object is to provide HSA crystals in a form suitable for drug binding studies.
Still another object is to provide a method of preparing such crystals.
Summary of the Invention In accordance with the present invention human serum albumin crystals are provided in the form of tetrag-onal plates having the space groups P42l2. These crystals may be readily grown to a size well in excess of 0.5mm in two dimensions and a thickness of 0.1 mm, this size enabling effective x-ray diffraction studies from which molecular configuration may be deduced. The crystals grow from solutions of polyethylene glycol, which will provide for the added advantage of solubilizing various pharmaceu-tical and biological compounds for binding studies. Human serum albumin is known to undergo substantial conforma-tional change with changes in pH. This crystal form isthe only one to grow under conditions of physiological pH, and therefore will provide the most relevant information with regard to drug binding studies. Crystallization conditions are reproducible, and the crystals diffract to resolutions adequate to determine the nature of the binding modes of various biological and pharmaceutical compounds. Crystals prepared in accordance with the .
invention may also prove useful in conduct of genetic engineering studies.
Crystal growth may be readily carried out by a "hanging-drop" method using a polyethylene glycol solution and a monobasic potassium phosphate buffering agent, with solution pH being adjusted prior to initiation of crystal growth.
Brief Description of the Drawings Details of the invention will become apparent from the accompanying drawings wherein:
Fig. 1 is a photograph showing a crystal of HSA
embodying the invention;
Fig. 2 is an x-ray precession photograph of such a crystal; and Fig. 3 is an x-ray oscillation photograph of an HSA crystal;
Fig. 4 is a schematic drawing showing a proposed packing arrangement of HSA molecules in crystals prepared in accordance with the invention.
Detailed Description of the Invention HSA crystals embodying the invention may be grown from a precipitant solution of polyethylene glycol (PEG), and a buffer, with concentration of reagents and pH being carefully controlled within prescribed limits. Any of the three basic techniques generally used for growth of protein crystals, that is, "hanging drop" or vapor diffu-sion, dialysis and batch methods may be employed, but the hanging-drop method is preferred.
In the hanging drop method a small drop of protein solution is placed on a cover slip, or glass plate, which is inverted over a well of solution and sealed. The solution in the well contains a precipitating agent, which is also present in a lesser amount in the protein droplet.
The function of the precipitating agent is twofold.
First, the solution in the well is initially at a lower vapor pressure than the protein droplet so that evapora-tion progresses at a rate fixed by the difference in the vapor pressures and the distance by which the vapor ~,,, (usually water) must diffuse. Secondly, the precipitating agent lowers the solubility of the protein in solution by competing with the protein for available solvent, and thus as evaporation from the protein droplet occurs the solu-tion becomes supersaturated in protein. Under the appro-priate conditions including pH, protein concentration and temperature, crystallization of the protein or macromole-cule then occurs.
The precipitant solution for use in the hanging drop method is made up to contain PEG at a molecular weight of 180 to 800, and preferably about 400 and a concentration of 35 to 45 volume per cent, with best results being obtained at 40 volume per cent, and a buffer in an amount sufficient to provide the required pH.
Monobasic potassium phosphate at a concentration of 0.05 to 0.lM may be used for this purpose. Other buffers such as sodium acetate, sodium citrate and Tris (hydroxymethyl) aminomethane-maleate may also be used.
I have found that the pH of the precipitant solution obtained after mixing of PEG and buffer is critical to effective and reproducible growth of HSA
crystals. A solution pH of 4.6 to 7.2 may be used, with best results being obtained at a pH of about 7.2. In a preferred procedure the precipitant solution pH is adjusted after mixing to compensate for variations in pH
which may arise from variation in molecular weight and residue content of PEG. Adjustment of pH is readily carried out by addition of small amounts of a solution of a base such as potassium hydroxide or an acid such as hydrochloric acid until the desired value is obtained.
HSA may be provided in the form of an aqueous solution at a concentration of 90 to 200 mg per ml. with best results being obtained at 200 mg per ml. Use of HSA
that is essentially free of fatty acids is preferred. In carrying out the hanging drop method a droplet of this solution, typically comprising 10 microliters, and a droplet containing an equal volume of precipitant solution would be placed on a cover slip and allowed to mix. A
~r-.~ , larger amount such as 1 ml of precipitant solution, without HSA, would be disposed in the well of the appara-tus.
Crystals grow from these periods in 3 to 10 days to dimensions of 0.5 X 0.5 X 0.5 mm to 2.0 X 2.0 X 0.3 mm.
The variations in the times for crystal growth are a function of protein concentration and pH. At concentra-tions of 200 mg per ml and pH values from 6.8 to 7.2 growth times are typically 5 days. For x-ray diffraction experiments the crystals are transferred from the hanging drop to a 10 to 20 microliter droplet of the corresponding reservoir solution, i.e. 40% PEG 400 in 0.05 M phosphate buffer. The crystals are stable in these solutions at 4C
for long periods of time. The pH of this stabilizing solution may be adjusted to enhance the binding of mole-cules for diffraction studies, in most cases without destroying the crystals.
The dialysis method utilizes a semipermeable size exclusion membrane which retains the protein but allows smaller molecules (buffers and precipitating agents) to diffuse in and out. Essentially identical conditions to those determined for the hanging drop method (or vice versa) can then be used to grow protein crystals. In dialysis, rather than concentrating the protein and the precipitating agent by evaporation, the precipitating agent is allowed to slowly diffuse through the membrane and reduce the solubility of the protein keeping the protein concentration fixed.
The batch methods generally involve the slow addition of a precipitating agent to an aqueous solution of protein until the solution just becomes turbid, at this point the container is sealed and left undisturbed for a predetermined time.
In practice, once the appropriate precipitating agent(s) buffer(s), and other experimental variables have been determined for any given growth method, any of these methods or others unmentioned could be used to grow crystals of a given protein. Thus these features as described above for growing HSA by the hanging drop method may also be applied to growing HSA by batch or dialysis methods.
The invention is further illustrated by the following specific examples.
Example 1 Crystals of HSA were grown from PEG using hanging drop procedures and apparatus. 5 ~1 portions of 35 to 40 per cent PEG (molecular weight 400) in 0.05M KH2PO4, pH
4.6, were added to equal portions of 120 to 180 mg/ml HSA, placed on glass cover slips inverted and sealed over wells containing 1 ml 40 per cent PEG in 0.1 M KH2PO4. Crystals appeared in 24 to 48 hours in the form of tetragonal plates and reached a size of 0.6 by 0.3 mm by .1 mm thick in 3 to 4 days. A photograph of one of the resulting crystals is shown in Fig. 1 of the drawings.
Crystals prepared as described above were trans-ferred to a stabilizing solution of 35 to 40 per cent PEG
400 in 0.1 M KH2PO4 and mounted in glass capillaries. X-ray precession photographs of resulting crystals were taken on a Supper camera with a Rigaku RU200 rotating anode source. An x-ray precession photograph thus ob-tained is shown in Fig. 2 of the drawings.
Example 2 HSA crystals were grown by the procedure of Example 1, except that the concentration of KH2PO4 was O.lM
in the precipitant solution, and solution pH was adjusted to 6.2 prior to mixing with HSA. Oscillation photographs were taken on an Enraf-Nonius Arndt-Wanacott camera at the Brookhaven Synchrotron Light Source operating at 2.5 GeV
with a beam current between 120 and 45 mA. An oscillation photograph so obtained is shown in Fig. 3 of the drawings.
X-ray precession photographs indicate 4 mm symme-try for the hko zone and lmm symmetry for the hhl, hO1 and Okl zones. The hOO and OkO zones show systematic absences for h or k = 2n + 1. There are no systematic absences along the 001 direction. The space group is therefore concluded to be P42~2. Consistent with the presence of an isotropic axis the crystals do not extinguish polarized light when viewed down the four fold axis. Unit cell constants as measured from precession photographs were found to be a=b=187(1) and c=81(1) A. A crystal density of 1.138 g/cm3 was determined using aqueous Ficoll (TM) gradients. This value for density indicates two protomers per asymmetric unit, which corresponds to a Matthews coefficient of 2.6 A3/dalton and implies a solvent content of 54 per cent.
Fig. 4 of the drawing illustrates a proposed orientation of the two molecules in the asymmetric unit of the P42~2 form. In this packing arrangement the shaded and unshaded molecules are related by a pseudo two-fold rotation forming a subcell with axes a' = b' = 132 A as required and possessing a molecular length of looA.
Packing considerations in this case appear to limit the molecular length to values of 130 A or less and values near 100 to 110 A seem more appropriate, although solution and electron diffraction studies estimate a molecular length of 140 A. The subcell shown in Fig. 4 would possess P422 pseudo-symmetry and contain one molecule per asymmetric unit.
While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.
r,~ ~
Technical Field This invention relates to protein crystal growth and more particularly to the preparation of crystals of human serum albumin in a form and size suitable for x-ray studies of crystal structure.
Background of the Invention Serum albumin, a protein of multiple functions and manifold applications, is one of the most extensively studied proteins in biochemistry. Over 25,000 literature citations involving the biochemistry and/or applications of serum albumins have been published since 1969. The mammalian serum albumins proteins are known to be the product of three tandem gene duplications, and possess high helical content (60%) and high cysteine content (17 disulphides) with approximate molecular weights in the range of 65,000 daltons. Complete amino acid sequences are known for bovine, rat, and human serum albumins.
Although the principal function of serum albumin remains unknown, it contributes to many transport and regulatory processes. Many studies have focused on the multifunctio-nal binding properties of this interesting protein which range from various metals, e.g., Ca and Cu, to fatty acids, hormones, and a wide spectrum of therapeutic drugs.
The majority of these binding studies have involved the human serum albumin (HSA) and many have shown that the distribution, free concentration, and metabolism of various pharmaceuticals can be significantly altered as a function of the magnitude of binding to HSA.
A detailed knowledge of the three-dimensional structure of serum albumin is imperative in order to fully understand the binding modes as well as many of the physical properties of this multifaceted protein. In addition, since many newly developed pharmaceuticals are rendered less effective by HSA; it is apparent that the crystal structure of a serum albumin, particularly the human form, will find very broad and significant applica-tion in the area of rational drug design. Consequently, the serum albumins have been the subject of ongoing crystallographic investigation which includes the documen-tation of several crystal forms (Table 1). Because of difficulties with crystal size, quality, and/or reproduci-bility, the three-dimensional structure of a serum albumin remains unknown.
This invention is concerned with the methodology required to produce a new crystal form of HSA which can be grown reproducibly as large, relatively high quality crystals suitable for x-ray structure determination. Once the three dimensional structure has been determined it will become possible to learn the molecular details involved in the binding of the albumin with a large number of pharmaceutical compounds. This may be done by soaking crystals in an appropriate stabilizing solution which contains the drug molecules of interest. If the binding sites are available in this crystal form, a crystalline array containing the serum albumin protein and the drug molecule will be produced. Details of the molecular interaction between the drug and protein can then be determined by established procedures in x-ray crystallog-raphy.
Due to the multiple binding capabilities of HSA, knowledge of its three dimensional structure combined with suitable crystals, may also provide assistance in deter-mining the structures of various small molecules and perhaps small proteins which have proven difficult to crystallize.
Crystals of human serum albumin have been known for some time. As early as 1952, large crystals of HSA
had been grown. Detailed x-ray examination of these and other reported crystal forms, including crystals of Horse serum albumin were published by McClure and Craven in 1974 (1) See Table 1, below. Crystals of HSA have also been grown by Rao and co-workers (2). Table 1 summarizes the crystallographic data published to date on several human serum albumin crystal forms. According to Peters in a recent review (1985) on serum albumins (3):
Although readily crystallized, albumin has relinquished few of its secrets through x-ray crystallography to date.
...Structural information from these crystals is awaited eagerly, but obtaining it appears to be fraught with obstacles.
Low described monoclinic crystals as soft waxy, and crystals studied by Rao, et al.
(1976) have tended to dissolve under study.
;~,.......................................................................... .
g V
0 0 ~ ~
~ ~N U U Ct 0` 8 X ~--1--~ 10 U t~ N N N U, 1--O ~ g Z N N0 ~ ' N o ~U U ~ 0 i C ~ N ~ o ~3 X -- U, 1 o ~- N 0 n u N ~ 1~1 N U~ -- . N
lU U~ ~o r~
O ~ O~
~ _ _ ~-- O --Ul C U~--N 8 m 5~ N _ 0 _ ~"
NU U U U~ ~_ 0~ o~ O C
C~C ~ O _ 1~1 ~ N U
.._ ._ ~ . o . j~.C
E _ L.u N ~ ~ N U~ ~< -- ~ _ 9- .C ~U ~ ~} C 4, o U U U U
~1-- U~ ~ O m 0 _ a V I ~ ~ CO
-c : <
a _ ~ _ . ~ a .. O
c . c o .. - ._ o 2 ~ o ~ ~ . Cl ~ : I ~ I 1' I _N~
~:.
~ ,.
Crystals of the monoclinic form reported by McClure and Craven appear to be the highest quality;
unfortunately, the crystals are small and difficult to reproduce. It is difficult to adequately compare the crystal quality of the remaining tetragonal crystal form with the tetragonal crystal form reported here, since the diffraction resolution reported for that crystal form was obtained with a conventional sealed tube source.
It is therefore an object of this invention to provide HSA in the form of crystals amenable to use in x-ray diffraction studies.
Another object is to provide HSA crystals having a size of at least 0.5mm in two dimensions.
Yet another object is to provide HSA crystals in a form suitable for drug binding studies.
Still another object is to provide a method of preparing such crystals.
Summary of the Invention In accordance with the present invention human serum albumin crystals are provided in the form of tetrag-onal plates having the space groups P42l2. These crystals may be readily grown to a size well in excess of 0.5mm in two dimensions and a thickness of 0.1 mm, this size enabling effective x-ray diffraction studies from which molecular configuration may be deduced. The crystals grow from solutions of polyethylene glycol, which will provide for the added advantage of solubilizing various pharmaceu-tical and biological compounds for binding studies. Human serum albumin is known to undergo substantial conforma-tional change with changes in pH. This crystal form isthe only one to grow under conditions of physiological pH, and therefore will provide the most relevant information with regard to drug binding studies. Crystallization conditions are reproducible, and the crystals diffract to resolutions adequate to determine the nature of the binding modes of various biological and pharmaceutical compounds. Crystals prepared in accordance with the .
invention may also prove useful in conduct of genetic engineering studies.
Crystal growth may be readily carried out by a "hanging-drop" method using a polyethylene glycol solution and a monobasic potassium phosphate buffering agent, with solution pH being adjusted prior to initiation of crystal growth.
Brief Description of the Drawings Details of the invention will become apparent from the accompanying drawings wherein:
Fig. 1 is a photograph showing a crystal of HSA
embodying the invention;
Fig. 2 is an x-ray precession photograph of such a crystal; and Fig. 3 is an x-ray oscillation photograph of an HSA crystal;
Fig. 4 is a schematic drawing showing a proposed packing arrangement of HSA molecules in crystals prepared in accordance with the invention.
Detailed Description of the Invention HSA crystals embodying the invention may be grown from a precipitant solution of polyethylene glycol (PEG), and a buffer, with concentration of reagents and pH being carefully controlled within prescribed limits. Any of the three basic techniques generally used for growth of protein crystals, that is, "hanging drop" or vapor diffu-sion, dialysis and batch methods may be employed, but the hanging-drop method is preferred.
In the hanging drop method a small drop of protein solution is placed on a cover slip, or glass plate, which is inverted over a well of solution and sealed. The solution in the well contains a precipitating agent, which is also present in a lesser amount in the protein droplet.
The function of the precipitating agent is twofold.
First, the solution in the well is initially at a lower vapor pressure than the protein droplet so that evapora-tion progresses at a rate fixed by the difference in the vapor pressures and the distance by which the vapor ~,,, (usually water) must diffuse. Secondly, the precipitating agent lowers the solubility of the protein in solution by competing with the protein for available solvent, and thus as evaporation from the protein droplet occurs the solu-tion becomes supersaturated in protein. Under the appro-priate conditions including pH, protein concentration and temperature, crystallization of the protein or macromole-cule then occurs.
The precipitant solution for use in the hanging drop method is made up to contain PEG at a molecular weight of 180 to 800, and preferably about 400 and a concentration of 35 to 45 volume per cent, with best results being obtained at 40 volume per cent, and a buffer in an amount sufficient to provide the required pH.
Monobasic potassium phosphate at a concentration of 0.05 to 0.lM may be used for this purpose. Other buffers such as sodium acetate, sodium citrate and Tris (hydroxymethyl) aminomethane-maleate may also be used.
I have found that the pH of the precipitant solution obtained after mixing of PEG and buffer is critical to effective and reproducible growth of HSA
crystals. A solution pH of 4.6 to 7.2 may be used, with best results being obtained at a pH of about 7.2. In a preferred procedure the precipitant solution pH is adjusted after mixing to compensate for variations in pH
which may arise from variation in molecular weight and residue content of PEG. Adjustment of pH is readily carried out by addition of small amounts of a solution of a base such as potassium hydroxide or an acid such as hydrochloric acid until the desired value is obtained.
HSA may be provided in the form of an aqueous solution at a concentration of 90 to 200 mg per ml. with best results being obtained at 200 mg per ml. Use of HSA
that is essentially free of fatty acids is preferred. In carrying out the hanging drop method a droplet of this solution, typically comprising 10 microliters, and a droplet containing an equal volume of precipitant solution would be placed on a cover slip and allowed to mix. A
~r-.~ , larger amount such as 1 ml of precipitant solution, without HSA, would be disposed in the well of the appara-tus.
Crystals grow from these periods in 3 to 10 days to dimensions of 0.5 X 0.5 X 0.5 mm to 2.0 X 2.0 X 0.3 mm.
The variations in the times for crystal growth are a function of protein concentration and pH. At concentra-tions of 200 mg per ml and pH values from 6.8 to 7.2 growth times are typically 5 days. For x-ray diffraction experiments the crystals are transferred from the hanging drop to a 10 to 20 microliter droplet of the corresponding reservoir solution, i.e. 40% PEG 400 in 0.05 M phosphate buffer. The crystals are stable in these solutions at 4C
for long periods of time. The pH of this stabilizing solution may be adjusted to enhance the binding of mole-cules for diffraction studies, in most cases without destroying the crystals.
The dialysis method utilizes a semipermeable size exclusion membrane which retains the protein but allows smaller molecules (buffers and precipitating agents) to diffuse in and out. Essentially identical conditions to those determined for the hanging drop method (or vice versa) can then be used to grow protein crystals. In dialysis, rather than concentrating the protein and the precipitating agent by evaporation, the precipitating agent is allowed to slowly diffuse through the membrane and reduce the solubility of the protein keeping the protein concentration fixed.
The batch methods generally involve the slow addition of a precipitating agent to an aqueous solution of protein until the solution just becomes turbid, at this point the container is sealed and left undisturbed for a predetermined time.
In practice, once the appropriate precipitating agent(s) buffer(s), and other experimental variables have been determined for any given growth method, any of these methods or others unmentioned could be used to grow crystals of a given protein. Thus these features as described above for growing HSA by the hanging drop method may also be applied to growing HSA by batch or dialysis methods.
The invention is further illustrated by the following specific examples.
Example 1 Crystals of HSA were grown from PEG using hanging drop procedures and apparatus. 5 ~1 portions of 35 to 40 per cent PEG (molecular weight 400) in 0.05M KH2PO4, pH
4.6, were added to equal portions of 120 to 180 mg/ml HSA, placed on glass cover slips inverted and sealed over wells containing 1 ml 40 per cent PEG in 0.1 M KH2PO4. Crystals appeared in 24 to 48 hours in the form of tetragonal plates and reached a size of 0.6 by 0.3 mm by .1 mm thick in 3 to 4 days. A photograph of one of the resulting crystals is shown in Fig. 1 of the drawings.
Crystals prepared as described above were trans-ferred to a stabilizing solution of 35 to 40 per cent PEG
400 in 0.1 M KH2PO4 and mounted in glass capillaries. X-ray precession photographs of resulting crystals were taken on a Supper camera with a Rigaku RU200 rotating anode source. An x-ray precession photograph thus ob-tained is shown in Fig. 2 of the drawings.
Example 2 HSA crystals were grown by the procedure of Example 1, except that the concentration of KH2PO4 was O.lM
in the precipitant solution, and solution pH was adjusted to 6.2 prior to mixing with HSA. Oscillation photographs were taken on an Enraf-Nonius Arndt-Wanacott camera at the Brookhaven Synchrotron Light Source operating at 2.5 GeV
with a beam current between 120 and 45 mA. An oscillation photograph so obtained is shown in Fig. 3 of the drawings.
X-ray precession photographs indicate 4 mm symme-try for the hko zone and lmm symmetry for the hhl, hO1 and Okl zones. The hOO and OkO zones show systematic absences for h or k = 2n + 1. There are no systematic absences along the 001 direction. The space group is therefore concluded to be P42~2. Consistent with the presence of an isotropic axis the crystals do not extinguish polarized light when viewed down the four fold axis. Unit cell constants as measured from precession photographs were found to be a=b=187(1) and c=81(1) A. A crystal density of 1.138 g/cm3 was determined using aqueous Ficoll (TM) gradients. This value for density indicates two protomers per asymmetric unit, which corresponds to a Matthews coefficient of 2.6 A3/dalton and implies a solvent content of 54 per cent.
Fig. 4 of the drawing illustrates a proposed orientation of the two molecules in the asymmetric unit of the P42~2 form. In this packing arrangement the shaded and unshaded molecules are related by a pseudo two-fold rotation forming a subcell with axes a' = b' = 132 A as required and possessing a molecular length of looA.
Packing considerations in this case appear to limit the molecular length to values of 130 A or less and values near 100 to 110 A seem more appropriate, although solution and electron diffraction studies estimate a molecular length of 140 A. The subcell shown in Fig. 4 would possess P422 pseudo-symmetry and contain one molecule per asymmetric unit.
While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.
r,~ ~
Claims (18)
1. A human serum albumin crystal in the form of tetragonal plates having space groups P4212 and a unit cell constant: a = b = 187(1)A, C-81(1).
2. A crystal as defined in claim 1, having a size of at least 0.5mm in two dimensions and a thickness of at least 0.05mm.
3. A crystal as defined in claim 2, having a size of 0.5 x 0.05 x 0.5mm to 2.0 x 2.0 x 0.3mm.
4. A crystal as defined in claim 1, having a crystal density of 1.138 g/cm3.
5. A method of growing crystals of human serum albumin which comprises:
providing an aqueous solution of human serum albumin at a concentration of 90 to 200 mg per ml;
providing an aqueous precipitant solution comprising polyethylene glycol at a concentration of 35 to 45 volume per cent and a buffer at a concentration so as to provide pH of 4.6 to 7.2;
mixing a droplet of said human serum albumin solution with a droplet of said precipitant solution;
suspending the resulting mixed droplet over a well of precipitant solution in a sealed container, the vapor pressure of the solution in said well being lower than in the resulting solution in the mixed droplet; and allowing the suspended mixed droplet to stand for a prolonged period until a human serum albumin crystal therein grows to a predetermined size.
providing an aqueous solution of human serum albumin at a concentration of 90 to 200 mg per ml;
providing an aqueous precipitant solution comprising polyethylene glycol at a concentration of 35 to 45 volume per cent and a buffer at a concentration so as to provide pH of 4.6 to 7.2;
mixing a droplet of said human serum albumin solution with a droplet of said precipitant solution;
suspending the resulting mixed droplet over a well of precipitant solution in a sealed container, the vapor pressure of the solution in said well being lower than in the resulting solution in the mixed droplet; and allowing the suspended mixed droplet to stand for a prolonged period until a human serum albumin crystal therein grows to a predetermined size.
6. The method of claim 5, wherein said buffer is mono-basic potassium phosphate.
7. The method of claim 6, wherein the concentra-tion of said buffer is 0.05 to 0.1 M.
8. The method of claim 7, wherein said precipi-tant solution is prepared by mixing a polyethylene glycol solution with a buffer and adjusting the pH of the result-ing mixed solution.
9. The method of claim 8, wherein said mixed droplet is allowed to stand for a period of 3 to 7 days.
10. The method of claim 9, wherein said mixed drop is allowed to stand until said crystal grows to a size of 0.5 x 0.5 x 0.05mm to 2.0 x 2.0 x 0.3mm.
11. The method of claim 10, wherein the molecular weight of said polyethylene glycol is 180 to 800.
12. The method of claim 11, wherein the average molecular weight of said polyethylene glycol is about 400.
13. The method of claim 12, wherein the concen-tration of human serum albumin in said aqueous solution is about 200 mg per ml.
14. The method of claim 7, wherein the pH of said precipitant solution is adjusted to a value of 6.8 to 7.2.
15. The method of claim 14, wherein said pH is adjusted to a value of about 7.2.
16. A method of growing crystals of human serum albumin which comprises:
providing an aqueous solution of human serum albumin at a concentration of 90 to 200 mg per ml;
providing an aqueous precipitant solution comprising polyethylene glycol at a concentration of 35 to 40 volume per cent and a buffer at a concentration so as to provide a pH of 4.6 to 7.2.
combining said human serum albumin solution with said precipitant solution and allowing the resulting solution to stand for a predetermined period until a human serum albumin crystal therein grows to a predetermined size.
providing an aqueous solution of human serum albumin at a concentration of 90 to 200 mg per ml;
providing an aqueous precipitant solution comprising polyethylene glycol at a concentration of 35 to 40 volume per cent and a buffer at a concentration so as to provide a pH of 4.6 to 7.2.
combining said human serum albumin solution with said precipitant solution and allowing the resulting solution to stand for a predetermined period until a human serum albumin crystal therein grows to a predetermined size.
17. The method of claim 16, wherein said human serum albumin solution is disposed within a semipermeable size exclusion membrane and said precipitant solution is combined with the human serum albumin solution by diffu-sion through said membrane.
18. The method of claim 16, wherein said precipi-tant solution is combined with said human serum albumin solution by slow addition thereto and the resulting solution is left to stand in sealed container.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/087,281 US4833233A (en) | 1987-08-20 | 1987-08-20 | Human serum albumin crystals and method of preparation |
| US087,281 | 1987-08-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1336530C true CA1336530C (en) | 1995-08-01 |
Family
ID=22204235
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000575341A Expired - Lifetime CA1336530C (en) | 1987-08-20 | 1988-08-22 | Human serum albumin crystals and method of preparation |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4833233A (en) |
| EP (1) | EP0357857B1 (en) |
| JP (1) | JPH064677B2 (en) |
| AU (1) | AU604958B2 (en) |
| CA (1) | CA1336530C (en) |
| DE (1) | DE3878239T2 (en) |
| FR (1) | FR2619567B1 (en) |
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| DE3927345A1 (en) * | 1989-08-18 | 1991-02-21 | Biotechnolog Forschung Gmbh | METHOD FOR DETERMINING THE STRUCTURE OF PEPTIDES |
| JPH08507916A (en) | 1992-06-09 | 1996-08-27 | カイロン コーポレイション | Crystallization of M-CSF |
| US5728553A (en) * | 1992-09-23 | 1998-03-17 | Delta Biotechnology Limited | High purity albumin and method of producing |
| US5554522A (en) * | 1994-04-28 | 1996-09-10 | Albert Einstein College Of Medicine Of Yeshiva University, A Division Of Yeshiva University | Dihydrodipicolinate reductase crystals and three dimensional structure |
| US5585466A (en) * | 1994-12-06 | 1996-12-17 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Crystals of serum albumin for use in genetic engineering and rational drug design |
| US5641681A (en) * | 1995-04-17 | 1997-06-24 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Device and method for screening crystallization conditions in solution crystal growth |
| US5978740A (en) * | 1995-08-09 | 1999-11-02 | Vertex Pharmaceuticals Incorporated | Molecules comprising a calcineurin-like binding pocket and encoded data storage medium capable of graphically displaying them |
| US6128582A (en) | 1996-04-30 | 2000-10-03 | Vertex Pharmaceuticals Incorporated | Molecules comprising an IMPDH-like binding pocket and encoded data storage medium capable of graphically displaying them |
| US6153579A (en) * | 1996-09-12 | 2000-11-28 | Vertex Pharmaceuticals, Incorporated | Crystallizable compositions comprising a hepatitis C virus NS3 protease domain/NS4A complex |
| US6020162A (en) * | 1997-06-13 | 2000-02-01 | The Rockefeller University | Crystal of a protein-ligand complex containing an N-terminal truncated eIF4E, and methods of use thereof |
| US5872011A (en) * | 1997-06-13 | 1999-02-16 | The Rockefeller University | Crystal of a protein-ligand complex containing an N-terminal truncated eIF4E, and methods of use thereof |
| US6183121B1 (en) | 1997-08-14 | 2001-02-06 | Vertex Pharmaceuticals Inc. | Hepatitis C virus helicase crystals and coordinates that define helicase binding pockets |
| US7383135B1 (en) | 1998-05-04 | 2008-06-03 | Vertex Pharmaceuticals Incorporated | Methods of designing inhibitors for JNK kinases |
| GB9902000D0 (en) | 1999-01-30 | 1999-03-17 | Delta Biotechnology Ltd | Process |
| US20020042046A1 (en) * | 1999-02-25 | 2002-04-11 | Vertex Pharmaceuticals, Incorporated | Crystallizable compositions comprising a hepatitis C virus NS3 protease domain/NS4A complex |
| US7250305B2 (en) * | 2001-07-30 | 2007-07-31 | Uab Research Foundation | Use of dye to distinguish salt and protein crystals under microcrystallization conditions |
| US7247490B2 (en) * | 1999-04-06 | 2007-07-24 | Uab Research Foundation | Method for screening crystallization conditions in solution crystal growth |
| ATE357656T1 (en) * | 1999-04-06 | 2007-04-15 | Univ Alabama Res Found | DEVICE FOR SCREENING CRYSTALIZATION CONDITIONS IN CRYSTAL GROWING SOLUTIONS |
| US20030022383A1 (en) * | 1999-04-06 | 2003-01-30 | Uab Research Foundation | Method for screening crystallization conditions in solution crystal growth |
| EP1701159A3 (en) * | 1999-04-06 | 2007-07-25 | University of Alabama | Method for screening crystallization conditions in protein solution crystal growth |
| US7244396B2 (en) * | 1999-04-06 | 2007-07-17 | Uab Research Foundation | Method for preparation of microarrays for screening of crystal growth conditions |
| US7214540B2 (en) * | 1999-04-06 | 2007-05-08 | Uab Research Foundation | Method for screening crystallization conditions in solution crystal growth |
| US6630006B2 (en) * | 1999-06-18 | 2003-10-07 | The Regents Of The University Of California | Method for screening microcrystallizations for crystal formation |
| US6296673B1 (en) | 1999-06-18 | 2001-10-02 | The Regents Of The University Of California | Methods and apparatus for performing array microcrystallizations |
| DE60233359D1 (en) * | 2001-02-09 | 2009-09-24 | Genentech Inc | Method for the identification of indirect IGF-1 agonists |
| EP1372571A4 (en) * | 2001-03-20 | 2006-06-07 | New Century Pharmaceuticals | Method and compositions for optimizing blood and tissue stability of camptothecin and other albumin-binding therapeutic compounds |
| US7670429B2 (en) * | 2001-04-05 | 2010-03-02 | The California Institute Of Technology | High throughput screening of crystallization of materials |
| CA2448432A1 (en) * | 2001-06-13 | 2002-12-19 | Taurus Hsa Llc | Purification of human serum albumin |
| KR20030022917A (en) * | 2001-09-11 | 2003-03-19 | 크리스탈지노믹스(주) | Method for crystallizing sortase |
| US20040137518A1 (en) * | 2002-01-31 | 2004-07-15 | Lambert Millard Hurst | CRYSTALLIZED PPARa LIGAND BINDING DOMAIN POLYPEPTIDE AND SCREENING METHODS EMPLOYING SAME |
| US20070026528A1 (en) * | 2002-05-30 | 2007-02-01 | Delucas Lawrence J | Method for screening crystallization conditions in solution crystal growth |
| US20040007672A1 (en) * | 2002-07-10 | 2004-01-15 | Delucas Lawrence J. | Method for distinguishing between biomolecule and non-biomolecule crystals |
| JP3567988B2 (en) * | 2002-07-11 | 2004-09-22 | 独立行政法人理化学研究所 | Method and apparatus for searching for crystallization conditions of biopolymer |
| CA2506317A1 (en) * | 2002-11-18 | 2004-06-03 | Taurus Hsa Llc | Method for continuous, automated blending of solutions from acids and bases |
| US7087719B2 (en) * | 2002-11-19 | 2006-08-08 | Gtc Biotherapeutics, Inc. | Method for the crystallization of human serum albumin |
| CA2565308A1 (en) * | 2003-05-06 | 2004-11-25 | New Century Pharmaceuticals | Albumin binding sites for evaluating drug interactions and methods of evaluating or designing drugs based on their albumin binding properties |
| CA2585115A1 (en) * | 2003-11-03 | 2005-05-12 | New Century Pharmaceuticals, Inc. | Albumin binding sites for evaluating drug interactions and methods of evaluating or designing drugs based on their albumin binding properties |
| US7507552B1 (en) | 2004-04-16 | 2009-03-24 | Takeda San Diego, Inc. | Crystallization of histone deacetylase 2 |
| US8176808B2 (en) * | 2007-09-13 | 2012-05-15 | Foster-Miller, Inc. | Robot arm assembly |
| US20140378537A1 (en) | 2011-09-09 | 2014-12-25 | Genentech, Inc. | Treatment of th17 mediated inflammatory diseases |
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| NL286954A (en) * | 1962-01-03 | |||
| US3869436A (en) * | 1971-06-01 | 1975-03-04 | Statens Bakteriologiska Lab | Method for fractionating plasma proteins using peg and ion-exchangers |
| US3790552A (en) * | 1972-03-16 | 1974-02-05 | Us Health | Method of removing hepatitis-associated antigen from a protein fraction using polyethylene glycol |
| DK25877A (en) * | 1977-01-21 | 1978-08-15 | Nordisk Insulinlab | PROCEDURE FOR EXTRACTING PURE ALBUMIN FROM BLOOD PLASMA |
| US4197238A (en) * | 1977-04-12 | 1980-04-08 | The Green Cross Corporation | Method of preparation of human albumin using polyethylene glycol |
| US4164496A (en) * | 1978-08-23 | 1979-08-14 | American National Red Cross | Preparation of albumin using PEG and EDTA |
| US4489133A (en) * | 1982-11-16 | 1984-12-18 | The Board Of Trustees Of The Leland Stanford Jr. University | Two-dimensional crystallization technique |
| US4668584A (en) * | 1985-12-23 | 1987-05-26 | General Electric Company | Method for forming 2-D crystals of proteins and macromolecules |
-
1987
- 1987-08-20 US US07/087,281 patent/US4833233A/en not_active Expired - Lifetime
-
1988
- 1988-08-19 AU AU21098/88A patent/AU604958B2/en not_active Ceased
- 1988-08-20 JP JP63205714A patent/JPH064677B2/en not_active Expired - Fee Related
- 1988-08-22 FR FR8811096A patent/FR2619567B1/en not_active Expired - Fee Related
- 1988-08-22 CA CA000575341A patent/CA1336530C/en not_active Expired - Lifetime
- 1988-09-05 DE DE8888402228T patent/DE3878239T2/en not_active Expired - Fee Related
- 1988-09-05 EP EP88402228A patent/EP0357857B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE3878239D1 (en) | 1993-03-18 |
| EP0357857A1 (en) | 1990-03-14 |
| FR2619567A1 (en) | 1989-02-24 |
| US4833233A (en) | 1989-05-23 |
| EP0357857B1 (en) | 1993-02-03 |
| JPH064677B2 (en) | 1994-01-19 |
| FR2619567B1 (en) | 1995-02-17 |
| AU2109888A (en) | 1989-02-23 |
| DE3878239T2 (en) | 1993-09-09 |
| JPH01238599A (en) | 1989-09-22 |
| AU604958B2 (en) | 1991-01-03 |
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