CA2205219A1 - Chemical modification of repetitive polymers to enhance water solubility - Google Patents

Abstract

Highly repetitive proteins which are relatively insoluble in water are chemically modified to increase solubility. The protein is reacted with a functionalizing agent to introduce additional polar functionalities and disrupt the order of the protein. The solubility of the protein in water is increased by the chemical modification, while adhesive and surfactant properties are retained.

Description

CA 0220~219 1997-0~-13 WO 96/16168 PCI~/US951129S9 CHEMICAL MODI~ICATION OF R~ E POLYMERS TO
ENHANCE WATER SOLUBILITY

INTRODUCTION
S Techni~l Field The field of this invention is chemic~lly modified, water-soluble protein polymers.

R~ round 10Protein polymers have been synth~si7ed with repeating domains of varying block size and mass ratios. Depending upon the nature of the repeating domain, the polymers of this sort may form a highly ordered structure of pleated beta-sheets. In general, as the total number of such blocks in a polymer is increased, the solubility of the polymer in water decreases. Also, the regularity of these syntheci7ed 15 repetitive unit proteins is much greater than the naturally occurring r~petiLi~e unit proteins from which the synth~ci7ed protein polymers are deci~ned. In the most extreme cases, proteins composed of almost 100% silk-like blocks are totally insoluble in water.
The vast majority of plastics have hydrophobic surfaces. For many applications such as cell culture and immunodiagnostics, it is critical to have a hydrophilic surface that aqueous fluids will wet. Current treatments commercially employed include plasma tre~tment to cause the formation of ionizable chemical groups on the surface, oxidation under conditions of irradiation, or by deposition of surfactants on the surface.
For many such applications, it is desirable to utilize the surfactant and adhesive plol)e Lies of such highly ordered protein polymers by depositing these CA 0220~219 1997-0~-13 ~teins onto hydlophobic surfaces from aqueous solutions. However, due to the insolubility in water, such protein polymers must be solubilized using strongly hydrogen bonding solvents such as > 85 % formic acid or using concentrated aqueous s~lutionc of salts high in the Hoffmeict~r series, such as 4.5 M lithiumS perchlor~t~ or lithium bromide.
Such solvents have de-fi~ien~ies for every day use. While ~ 85 % formic acid is a good solvent and is fully volatile, it is corrosive and the vapors are noxious.
When using the aqueous salt solutionc, the salt residues are corrosive and noxious.
While one can devise a coating process which begins by preparing a relatively 10 conce.,LIdted stock solution of protein polymer in a solvent such as those described above, and then diluting to the proper working concentrations using water as thediluent, this approach does not solve the problems indicated above. In addition,often, these diluted working solutions are met~ct~hle, and change their deposition char~ctt-rictics with time.
The noxious and corrosive col,lponents of the ~Yi~ting solvent systems complic~tes the design of coating processes involving protein polymers with highly ordered structures. It is therefore of considerable value to provide methods of modifying such protein polymers to improve their solubility in water.

20 Relev~nt ~ i~e~
]Uetho-lc for producing recombinant repe~ting-block proteins are described in U.S. Patent no. 5,243,038, issued on 9/07193; and International Application PCT/US89/05016.
SUMMARY OF THF. INVF~TION
Methods and compositions are provided for the preparation and use of water soluble re~ ilive unit proteins by chernic~l modification of water insoluble repetitive unit proteins composed of repe~t;ng blocks of amino acid sequence. The solubility of the protein in water is increased by reaction of a polar small molecular weight reactant with available function~lities on the protein. The resultin~ product is water 30 soluble, can be coated onto plastic and strongly adheres, and retains active functional sequences, particularly biological functional sequences, present in the parent col,lpound CA 0220~219 1997-0~-13 nF~CR~ ON OF .~PF.~IFIC Fl\~ROnTMF.~TS
~Uethods and cG,,,I~os;~ ns are provided, whereby proteins having low water solubility are chemir~lly motlified by adding low molecul~r weight organic groups to available fi~nction~lities to produce products which are water soluble, but strongly adhere to a plastic surface, even in the p,ese,lce of an aqueous medium over long periods of time. Of particular interest are high molecular weight proteins whereeYtPnded sllelches of small ~epe~lin,E~ units comrrice a major portion of the protein.
The proteills are typically of relatively high molecular weight, being greater than about 6 kD, usually greater than about 10 kD, preferably more than 20 kD and generally less than about 250 kD, usually less than about 150 kD, more usually less than about 125 kD. The protein will be repetitive, that is, compri~e~ of l~eating units, where the individual units will have from 3-30 amino acids (9-90 nt), more usually 3 to 25 amino acids (9-75 nt), particularly 4 to 15 amino acids (12-45 nt), more particularly 4 to 12 amino acids (12-36 nt), usually having the same amino acid appe~ g at least twice in the same unit, generally sep~d~ed by at least onearnino acid. For the most part, the naturally oc~;u~ g repeating units will be from about 4 to 8 amino acid l~ g units, particularly, 4 to 6 amino acid units.
Di~îe,~;nt amino acid l~t;~i~ive unit combinations may be joined together to form a block copolymer or ~ltern~ting block copolymer.
The protein will have a ci~nific~nt l.r~G"ion of the total amino acids with a reactive functionality, which includes hydroxyl, sulfhydryl, carboxyl, and amino, particularly hydroxyl or sulfhydryl group, e.g. serine, threonine, tyrosine, cysteine, lysine, arginine, hi~ti(line, aspartic acid and glutamic acid. Usually at least about 2 % by number of amino acids, more usually at least about 5 % by number, and 25 preferably at least about 10% by number, and usually not more than about 30%,more usually not more than about 20% will have the reactive functionalities involved in function~li7~tion of the protein. Desirably, the reactive group is hydroxyl, where the hydroxyl group involved in the functionalization may vary with the function~li7ing group, e.g. tyrosine reacting with an oxirane and serine reacting with 30 a sultone.
Suitable proteins for modification will have a highly ordered, usually semi-crystalline structure, with a high degree of extended ~ and ,B-turn conformations.

CA 0220~219 1997-0~-13 The protein solubility in deionized water will usually be less than about 1.0 mg/ml, more usually less than about 0.1 mg/ml, at ambient conditions. After the subject~hPmi~l mo~lifi~tion the solubility will be at least about 10 mg/ml, more usually at least about 100 mg/ml at ambient con.litionc.
The protein will be modified by reaction with a function~li7in~ reagent, e.g.
an alkylating agent, or an acylating agent, where a single reagent or a combination of reagents may be employed, usually not more than about 3 reagents, more usually not more than about 2 reagents. Suitable reagents will be of from about 2 to 8, frequently 2 to 6 carbon atoms, usually 2 to 4 carbon atoms for other than ammonio, 10 and usually 5 to 8 for ~mmonio, having from 1 to 4 heteroatollls, which will be chalcogen (oxygen and sulfur), and nitrogen, particularly as amino having from 1 to 4 substituçntc. Functionalities will include epoxides of from 2 to 4, usually 2 to 3 carbon atoms, acyl groups of from 2 to 8, usually 2 to 6 carbon atoms, where theacyl group may have from 0 to 2 oxy groups of from 0 to 2 carbon atoms, or amino15 group of from 0 to 4 carbon atoms, particuarly ~mmonio, lactones of from 3 to 5 carbon atoms, particularly sulfonate lactones (sultone) of from about 3 to 8 carbon atoms, and substituted active olefin or active halogen, of from about 2 to 8 carbon atoms, usually 2 to 6 carbon atoms and preferably 2 to 3 carbon atoms for other than ammonio substituted, usually having from 1 to 3 heteloato",s, as described above.
20 The resulting substituents are illustrated by hydroxyethyl, hydroxypropyl, dihydroxypropyl, dihydroxybutyl, carboxymethyl, carboxyethyl, cyanoethyl, trimethyl~mmonioethyl, 2-hydroxy-4-dimethylammoniobutyl, sulfonatopropyl, trimethyl~mmonio~cetyl, methoxyacetyl, and the like. Particular reactants include ethylene oxide, propylene oxide, hydroxypropylene oxide, epichlorohydrin, chloroacetic acid, trimethylammonioethylchloride, trimethylammoniopropylene oxide, acrylonitrile, methacrylamide, dimethylaminoethylchloride hydrochloride, etc. The reaction will usually proceed by a nucleophilic substitution at the carbon of the reagent, with retention of the amino acid heteroatom, particularly base catalysed nucleophilic substitutiQn.
As a first step the protein willl be solubilized in a suitable solution in whichthe reaction can occur, usually using concentrated aqueous solutions of salts, which are both high in the Hoffmçi~ter series and whose anions are substantially inert to CA 0220~219 1997-0~-13 the function~li7ing reagent(s), usually at least about 2 M concentration, more usually at least about 4.5 M. Examples of suitable Hoffmei~ter salts are lithium perchlorate and pot~ m sulfate. For base catalyzed reactions, the pH of the solution may then be raised to at least about 9, more usually to least about 11, or at least about lOmM, S depen-lin~ on the nature of the organic reactant. The function~li7ing reagent will usually be added in at least 2 fold molar excess, usually at least about 10 foldexcess, based on available reactive groups in the protein composition for the particular reaction. The reaction will proceed until at least about 1 % of the reactive amino acid residues have been morlifi~i, more usually at least about 10% of the 10 reactive residues have been modified, and usually not more than about 80%, more usually not more than about 60% of the reactive residues have been modified. At room tempe,~ture the reaction will usually be complete in about 6 hours, more usually about 3 hours. The reaction is stopped by lowering the pH to about 7.0 to 7.5. The modified protein may be purified by conventional methods.
Depending on the sçlected conditions, some degradation of the protein may occur. By using strongly basic conditions for extended periods of time, e.g. > 2M, for extended periods of time, e.g. > lh, particularly at high ionic strength, e.g.
> 2M LiCl04, the molecular weight of the protein may be reduced by about half.
Therefore, by selecting the reaction conditions, one can provide for a product which 20 has a lower or about the same molecular weight of protein, plus the additional weight of the re~ct~nt Proteins of interest include structural proteins such as elastin-, collagen-, keratin-, and silk-like proteins, preferably, synthetic protein polymers, particularly proteins designPd with silk-like protein repelilive units, where blocks of repetitive 25 units, generally blocks of 2 to 50 l~eli~ive units, are separated by sequences of from about 3 to 50, more usually 3 to 35 amino acids including a sequence which has chemical or physiological activity, e.g. cell receptor binding, such as in b~cement membrane proteins, ligands for receptors, homing proteins, etc. These proteins include the RGDS sequence (fibronectin), the IKVAV sequence (l~minin), 30 cysteine, lysine, aspartic acid, histidine, etc., and other groups, as described in US
Patent Application Nos. 609,716 and 114,618, and PCT/US87/02822 and PCT/US89/05016, where numerous repetitive unit proteins are described, as well as CA 0220~219 1997-0~-13 dirre.e,lt intervening sequences, which references are incorporated herein by reference. The polypeptides may be natural, chemically synthesi7ed, or recombinant proteins, inclll~ling mo~ified forms such as mutants and fusion products.
Silk-like proteins have as a repeating unit GAGAGS (G = glycine; A =

5 ~l~nine; S = serine). This r~pe~ g unit is found in a naturally occurring silkfibroin protein. The N-terminus and C-terminus may be different sequences, generally of from about 1 to 125 amino acids, usually of from about 1 to 60 amino acids, usually fewer than 20%, more usually fewer than about 10% of the total amino acids of the protein. For the most part, there will be no particuar pattern of 10 amino acids in the terminal sequences. Of particular interest are proteins which mimic the composition and physical pr~pel Lies of silk of Rombyx mori. Generally, dirrerenl ter~ ii will be the result of insertion of the gene into a vector in a manner that results in e.~plession of a fusion protein. Any protein which does not inlelrere with the desired pl~ellies of the product may provide the one or both terminii.
15 Particularly, endogenous host proteins, e.g. bacterial proteins, may be employed.
The terminii are not critical to the subject invention, are primarily for convenience, but should not intelrer~ with the desired prupelLies of the protein, and may be decign~d for proteolytic cleavage.
Of particular interest is a motif having a base sequence of about 2 to 10, 20 preferably 8 to 9, individual repeating units, usually separated by a sequence of about 5 to 160 amino acids, usually 8 to 50 amino acids, which may include an internal repeat different from the individual repeating unit of from 3 to 30 amino acids, which will normally result in modification of the physical properties and the structure of the protein. For example, by introducing elastin repeats in a fibroin-25 like-polymer, one can provide for greater elasticity and flexibility, in co..,palison to the fibroin-like-polymer. Thus, one may have block copolymers, where the prul)el ~ies can vary between the nature of the homopolymers of the individual repeat units. The total number of base repeating units will generally be in the range of about 50 to 300, usually 75 to 250.
Physical measurements of purified silk-like proteins, prepared by recombinant techniques and described subsequently, confirm the model of anti-parallel chain pleated sheet conformation for the crystalline regions of Bombyx mori CA 0220~219 1997-0~-13 WO 96/16168 PCI~/US951129S9 silk fibroin. Circular dichroic (CD) and Fourier transform infrared (FIIR) ~ecLroscopic analysis are consistent with a high degree of extended B and B-turnconfoi.,~l;on~. Comp~ ons of the spectra obtained from a silk-like protein (SlpIII
des~ihed in the patent references indiçatPd above) with that of naturally occurring S silk fibroin in various solvents indic~te that SlpIII in solution consists of a mixture of the random and highly ordered structures seen in silk fibroins.
A silk-like protein comprising intervening RGDS sequences (referred to as SLPF or FCB-SLP protein in the patent references in~ ted above, and sold as ProNectin~-F, Protein Polymer Technologies, Inc., San Diego, CA) is characterized 10 by having strong adhesive plope.lies. On coating a plastic or glass surface, e.g.
polystyrene, Bioglas, polyacrylates, etc., particularly thermal molding and extrusion p~ ti5~s~ a strong adherent coating is obtained, which is stable over extended periods, e.g. 30 days and more, in cellular culture. After modification, the adhesive pr~ellies as idçntifiPd above are not substantially altered.
The protein co~ )ounds can be provided as aqueous solutions, where the salt content does not exceed 1 M, usually less than about .5 M, and may be deionized water. Usually the protein compound will be present in the aqueous solution at at least about 0.001 weight %, and may be 0.01 weight ~ or more, usually not more than about 90 weight %, and may be provided as solutions for direct use for coating 20 or other purpose, as concentrates of at least about 10 weight %, or as compositions with other components appr~.iate for its intended purpose. The particular concentration of the protein in the solution will depend on the nature of the protein, its solubility, the intçntled application, other components in the solution, and the like. For example, the coating of biiologicaly functional proteins onto plastic 25 substrates can be conducted at extremely low concentrations, whereas solutions for the spinning of fibers will be highly concentrated.
The modified proteins are particularly useful for coating plastic surfaces.
The increased water solubility allows coating procedures to take place in non-toxic solvent systems where various convenient methods of application may be employed 30 without concerns about the hazards of the previously used solvents. As numerous applications involve contact with viable biological cells or tissue, biocompatible plastics are çspeci~lly p~ere~led. Biocompatible plastics are typically non-toxic, CA 0220~219 1997-0~-13 8 PCI~/IJS951129S9 bioch~mic~lly inert. Exemplary bioco-~patible plastics include polycaprolactone,polycarbonate, polydimethylsiloxane (silicone rubber), polydioxanone, polyether ur~lhane, polyethylene and polyethylene terphth~l~te, polyglycolic acid and polylactic acid and PLGA copolymers, polystyrene, polyhydroxyethyl meth~crylate S (HEMA), polymethylmeth~rylate (acrylic), polyvinyl chloride (PVC), etc.
The plastic substrate may take many forms, where the plastic substrate may be labware, e.g. Petri dishes, culture bottles, Erlenmeyer flasks, slides, roller bottles, multiwell plates, or other labware where an adherent coating is desirable, for example, in which cells may be grown; devices where an adherent protein 10 coating is desired, such as devices introduced in vivo, where the bare plastic surface of the device may cause an adverse physiological response; and fibers or films, where one wishes to modify the surface charactçristics of the material; and the like.
The solution may be applied to the surface by painting, spraying, dipping, or so~kin~.
Additives may be included in the solutions, such as stabilizers, buffers, detergents, spreading agents, or the like, generally being present in total in less than about 5 weight % of the solutin, generally less than about 1 weight % of the sqlution.
The following examples are offered by way of illustration and not by way of 20 limit~tiQn.

~;X~KIMENTAL
The names of the polymers and their pr~pal~tion may be found in U.S.
Patent No. 5,243,038 and application serial no. 07/609,716, filed November 6, 25 1990.
Hydrv~y~ropylated SLPF
SLPF (ProNectin0-F, Protein Polymer Technologies, Inc., San Diego, CA) (100 mg) was dissolved in 5.0 ml of 4.5 M lithium perchlorate in water. Solid NaOH (19 mg) was dissolved in the mixture with stirring at room temperature.
30 Propylene oxide (600 ~1) was added in two portions of 300~1 each, stirring at room ~e",peld~u~e for 2 hours after each addition. The reaction mixture was poured into 45 ml of water and was neutralized to pH 7.0 - 7.5 using dilute aqueous CA 0220~219 1997-0~-13 hydr~llloric acid. The Illixlul~ was dialyzed for 24 hours against deionized water using a 13 kDa cutoff cellulose membrane (Spectrum Medical Devices). A slight p,~cip;l~le (4.8 mg) was removed by filtration through a tared filter paper. The~ inin~ very slight cloudiness was removed by filtration through a pad of Celite5 545 to yield a clear solution of pH 6.5. This solution was concentrated on the rot~ry e~ )o,ator to a~pro~h~tely 10 ml before being again dialyzed against deionized water for 24 hours using a 13 kDa cutoff cellulose membrane. The contents of thedialysis bag were shell frozen in a 100 ml pear shaped flask and lyophilized to a final pleS:~Ule of 75 mTorr at 25C. A white fluffy fibrous solid (42.8 mg) was 10 recovered. This material was decign~ted HP-PnF, and was observed to be readily soluble in dei~lli7~d water.
The gel electrophoresis of this material shows a set of bands which migrate at about half the molecul~r weight of the starting m~teri~l, indic~ting approximately one hydrolytic chain scission per molecule occurred during the reaction chemictry.
15 The reactivity of the silk fibroin antibody to HP-PnF was observed to be less intense than with native SLPF as judged from the intensity of the development bands on the gel and the known mass of protein sample applied to the gel.
Hydroxypr~"~laled SLP3.0 Crude SLP3.0 (100 mg) was slurried in 4.5 ml of 4.5M lithium perchlorate 20 and stirred for 24 hours at room te"lpel~ture to yield a brown particulate suspension in a viscous solution. Celite 454 (50 mg) was added, stirred, and centrifuged tocompact a brown pellet (ca. 0.3 ml volume) and provide a clear supernatant solution. The supernatant was dec~nted. To the supernatant, was added NaOH (20 mg) dissolved in 0.50 ml of 4.5 molar lithium perchlorate solution. Propylene oxide 25 (300~1) was added in one portion and the mixture stirred for 6 hours at 35C. A
second portion of propylene oxide (300 ~l) was added and the mixture stirred for 2 hours. Water (5.0 ml) was added and the reaction mixture was neutralized to pH
7.0 with dilute aqueous hydrochloric acid. The solution was dialyzed through a 13 kDa cutoff cellulose membrane for 48 hours against deionized water. Slight 30 cloudiness in the product solution was removed by centrifugation to yield a clear supernatant and a pellet (ca. 0.2 ml). The supernatant was shell frozen and lyophilized to a final pressure of 75 mTorr at 25C to yield a white fluffy m~tt~ri~l _g_ CA 0220~219 1997-0~-13 WO 96/16168 PCI~/US95112959 (39 mg). This material was decign~t~d HP-SLP3.0; and was observed to be readily soluble in deionized water.
The gel electrophoresis of this material shows a set of bands which migrate at about half the molecular weight of the starting material, indic~ting approximately 5 one hydrolytic chain scission per molecule. The reactivity of the silk fibroinantibody to HP-SLP3.0 was observed to be less intense than with native SLP3.0 asjudged from the intensity of the development bands on the gel and the known massof protein sample applied to the gel.
Dilllelhyl~...;nQethylated SLP3 Crude SLP3.0 (1.0 g) was stirred with 25 ml of 4.5M LiCl04 for 16 hr.
Undissolved suspended solids were removed by centrifugation using a S534 rotor at 15,000 rpm for 20 min. A light yellow clear supc~nat~lt (23.5 ml) was recovered and used subsequently. Four portions of dimethylaminoethylchloride-HCl (0.72 g, 5 mMole) and sodium hydroxide (0.40 g, 10 mMole) were added, stirring 30 min.
15 after each portion. Acetic acid (1140 ~L) was added to adjust to pH 6.5. The neutralized solution was placed in a 13 kDa cutoff dialysis bag and dialyzed against deionized water for 24 hr. The lcl~nt~te was filtered through a pad of Celite 545 on a Ruchn~r funnel, concentrated on the rotary evaporator, and dialyzed through a 13 kDa cutoff dialysis bag against dPioni7çd water for 24 hours. The retentate was 20 shell frozen and lyophilized to yield 39.5 mg of white product. This material was de~ign~ted DMA-SLP3.0 and was observed to be readily soluble in deionized water.Sulfopropylated SLP3 Crude SLP3.0 (1.0 g) was stirred with 25 ml of 4.5M LiCl04 for 16 hr.
Undissolved suspçnded solids were removed by centrifugation using a S534 rotor at 25 15,000 rpm for 20 min. A light yellow clear supernatant (23.5 ml) was recovered and used subsequently. Four portions of propane sultone (1.22 g; 876 ~L; 10 mMole) and sodium hydroxide (0.40 g, 10 mMole) were added, stirring 30 min.
after each portion. Acetic acid (600 ~L) was added to adjust to pH 6.5. The neutralized solution was placed in a 13 kDa cutoff dialysis bag and dialyzed against 30 deionized water for 24 hr. The retentate was filtered through a pad of Celite 545 on a Buchner funnel, concentrated on the rotary evaporator, and dialyzed through a 13 kDa cutoff dialysis bag against deionized water for 24 hours. The retçnt~te was WO 96/16168 PCrrUS951129S9 shell frozen and lyophi1i7~ to yield 160 mg of white product. This material was deci~n~t~1 SP-SLP3.0 and was observed to be readily soluble in deionized vvater.Sulfopro~ led SLPF
SLPF (103 mg) and 3.0 ml of 4.5 molar aqueous lithium perchlorate was - S added to a 10 ml Erlenmeyer flask fitted with a rubber septum cap and ~ ted by a m~neti~ stirrer. The head sp~ce was purged with nitrogen and stirring commenced at ambient te~ el~tul~. Propane s~ltone, dissolved in 2.0 ml of tetrahydrofuran,was added in one portion to yield a homogeneous mixture. A solution (1.0 ml) of sodium hydroxide (40 mg) dissolved in 4.5 molar aqueous lithium perchlorate was then added by syringe pump at a rate of 0.019 ml/min. After stirring for an additional 30 minutes a solution of acetic acid (60 mg) in water (1.0 ml) was added in one portion and the reaction mixture was transferred to a 13 kDa cutoff dialysis bag and dialyzed against 15 L of deionized water for 24 hr. The water was replaced and dialysis was continued for an additional 24 hours. The retentate was shell 15 frozen and lyophili7ed to yield 90 mg of white product. This material was dçci~n~tell SP-SLPF and was observed to be readily soluble in deionized water.
Dimethyl~minoe~hylated SLPF
SLPF (103 mg), dimethylaminoethylchloride hydrochloride (360 mg), and 3.0 ml of 4.5 molar aqueous lithium perchlorate were added to a 10 ml Erlenmeyer20 flask fitted with a rubber septum cap and agitated by a magnetic stirrer. The head space was purged with nitrogen and stirring commenced at ambient temperature. A
solution of sodium hydroxide (200 mg) dissolved in 4.5 molar aqueous lithium perchlorate (2.65 ml) was then added by syringe pump at a rate of 0.174 ml/min.
After stirring for an additional 60 minutes, acetic acid was used to adjust to pH 6.0-25 6.5, and the reaction mixture was transferred to a 13 lcDa cutoff dialysis bag anddialyzed against 15 L of deionized water for 24 hr. The retent~te was shell frozen and lyophilized to yield 63 mg of white product. This material was design~t~d DMA-SLPF and was observed to be readily soluble in deionized water.
- Amino Acid Comp~;tiQnc The amino acid composition of the derivatized protein polymers were determined by the PTC derivatization procedure of Henrickson and Meredith (1984).
Protein samples were hydrolysed with 5.7 N constant boiling hydrochloric acid at CA 0220~219 1997-0~-13 WO 96/16168 PcrluS95tl29S9 108 C for 24 hours in vacuo. After reaction with PITC, amino acid derivatives were detP~t~l at 254 nm by HPLC reverse phase chromatography using a Hewlett Packard 1090 system and a Supelco C18 column (4.6 mm x 25 cm) with a linear gradient of 0 - 50% ~cetoll;L~ .le in 0.1 molar ammonium acetate pH 6.78 as a mobile 5 phase. ~nri~ on, R.L. and Meredith, S.C. (1984) Amino Analysis by Reverse Phase High P~lrol.l,allce Liquid Chromatography. An~l. Riochem. 137:65-74. The norm~li7~d results of these analyses are presented in Tables 1 through 5 for HP-PnF, HP-SLP3.0, DMA-SLP3.0, SP-SLP3.0, and SP-PnF respectively .

Table 1 Norm~li7ed Amino Acid Compositions of HP-PnF.
Component picoMole Ratios Ratios Deficit (found) (theoret) (found) L-Glycine 6623 30 30 0 L-Alanine 4707 23 21.3 -7%
L-Serine 2091 11 9.5 -14%
L-Tyrosine 57 1 0.3 -70%
L-Threonine 201 1 0.9 -10%

Table 2.
20Norm~1i7ed Amino Acid Compositions of HP-SLP3Ø
Component picoMole Ratios Ratios Deficit (found) (theoret) (found) L-Glycine 6774 29 29 0 L-Alanine 4520 20 19.4 -3 %
L-Serine 1831 9 7.8 -14%

L-Tyrosine 60 1 0.3 -70%

Table 3.
Norm~1i7Pd Amino Acid Compositions of DMA-SLP3Ø
Co.n~ol-f -tpicoMole Ratios Ratios Deficit (found) (theoret) (found) ..
L-Glycine 2487 29 29 0 L-Alanine 1621 20 18.9 -5%
L-Serine 602 9 7.0 -22 %
L-Tyrosine 74 1 0.9 -10%

Table 4.
Norm~li7~d Amino Acid Compositions of SP-SLP3Ø
Component picoMole Ratios Ratios Deficit (found) (theoret) (found) L-Glycine 4856 29 29 0 L-Alanine 3135 20 18.7 -6%
L-Serine 632 9 3.8 -58%
L-Tyrosine 67 1 0.4 -60%

Table 5.
Norm~li7ed Amino Acid Compositions of SP-PnF.
Col,lponent picoMole Ratios Ratios Deficit (found) (theoret) (found) L-Glycine 4269 30 30 0 L-Alanine 2972 23 20.9 -9 %
L-Serine 1426 11 10.0 -9%
L-Tyrosine 133 1 0.9 -10%
L-Threonine 143 1 1.0 0 CA 0220~219 1997-0~-13 wo 96/16168 Pcrluss5ll2959 In the cases of SP-SLP3.0 and of SP-PnF, the deficits of amino acids can be verified by means of microchemic~l analysis of the elernent~l compositions of the pluleins and c~l~ul~tion of the molar ratio of sulfur to nitrogen. Both the SLP3.0 and SLPF molecules are initially devoid of sulfur, and each functionalization event 5 introduces a single 3-sulfopropyl moiety. Thus the molar ratio of sulfur to nitrogen is a l1æas.~l~ of the extent of the function~li7~tion reaction.
From the observed deficits of amino acids in SP-SLP3.0, the predicted ratio of S/N = 0.120. From microanalysis of elçrn~nt~l composition of this functionalizedprotein, the 111~- l~d ratio of S/N = 0.119. From the observed deficits of amino acids 10 in SP-PnF, the predicted ratio of S/N = 0.042. From microanalysis of çlçlnent~l composition of the function~li7e~ protein, the measured ratio of S/N = 0.034. Thus data on elçment~l compositions and on amino acid compositions are consistent with each other.
The data in Table 1 through 5 focus on the amino acids which make up the silk 15 fibroin region (GAGAGS) of these protein polymers containing silk-like regions. In all cases, the norm~li7~1 ratios indicate a depletion of L-serine. Such results implicate the L-serine residues as the primary sites of the various etherification reactions, through reaction on the side chain hydroxyls.
An ~aLkylated residue of L-serine in the modified protein polymer is expected 20 to hydroly_e back to an amino acid, but not to cleave back to native L-serine under the cQn~iti()n~ of the acid hydrolysis step of the amino acid compositional analysis. Thus, the absolute content of L-serine observed in the modified protein polymers will appear to be reduced, as is observed. On a basis of this compositional data, function~li7~tion occurs on from 9% to 58% of the L-serine residues.
The reactivity of the antibody to silk fibroin depends upon recognition of the GAGAGS epitope. If a ch~rnic~l modification occurs at the most prominent chemical group within this epitope, the hydroxyl side chain on the L-serine residue, then a reduced reactivity with the antibody would be anticipated. Qualitatively, such reduced reactivity with the antibody is observed in the cases of HP-PnF and HP-SLP3Ø

WO 96/16168 PCr/US951129S9 Atta~h..~ ..' of VERO Cells On Pol~ ,.c Coated With HP-PnF
In order to judge the co",~t~nce of HP-PnF with respect to surfactant activity and cell ~tt~rhm~nt activity, a cell ~tt~hmpnt assay was pclrol",ed on a multi-well polystyrene tissue culture plate with 96 wells. In this assay, ProNectin F (PnF) was 5 made up in 4.5 molar lithium perchlorate at 1.0 mg/ml and was serially diluted with ph~l.h~ burre~cd saline to the final coating concentrations. The HP-PnF was madeup in deionized water, and seAally diluted with deionized water. Each dilution was applied to one lane of 8 wells on the plate. Blocking, inoc~ tiQn with cells, incubation, fis~tion, and st~inin~ with amido blue black dye were all conducted 10 according to standard protocols. Relative cell numbers were estim~t~
~cllul)hoto..-e~ lly at 495 nm. The results of this cell ~tt~-hment assay are reported in Table 6.
Table 6.
VERO Cell Attachment On Serially Diluted ProNectin~F And On Serially Diluted HP-PnF
Coating SolutionDoseperWell Absorbance Absorbance (~g/ml) (g/well) PnF HP-PnF
2.0 x 10~ 0.775 i 0.024 0.758 + 0.031 4.0 4.0x 1o-7 0.761 + 0.016 0.799 + 0.038 0.80 8.0x 10-8 0.781 + 0.021 0.795 +0.019 0.16 1.6 x 10-8 0.764 + 0.026 0.776 + 0.015 0.032 3.2x 10-9 0.771 + 0.033 0.768 + 0.024 0.0063 6.3 x 10l 0.737 + 0.040 0.558 + 0.075 O O O O
Att~rhmPnt of VERO Cells On Poly~lyr~l.e Coated With SP-PnF
In order to judge the competence of SP-PnF with respeet to surfactant activity and cell ~tt~chment activity, a cell attachment assay was performed on a multi-well polystyrene tissue culture plate with 96 wells. In this assay, ProNectin F was made up 30 in 4.5 molar lithium perchlorate at 1.0 mg/ml and serially diluted with phosphate buffered saline to the final coating concentration of 10 ~g/ml, and then applied to the first lane of 8 wells. The SP-PnF was dissolved in deionized water at 1 mg/ml and diluted to the final coating concentrations of 10 ~g/ml, 1.0 ~g/ml, and 0.10 ,ug/ml.
Each dilution was applied to two lanes of 8 wells on the plate. Blocking, inoculation with cells, incub~tion~ fil~tion, and st~ining with amido blue black dye were all S conducted accor~in~g to standard plolocols. Relative cell numbers were e~stim~ted s~ecl~ophotometriç~lly at 495 nm. The results of this assay are r~pol~ed in Table 7.
Table 7.
VERO Cell ~tt~hm~nt On ProNectin0F And On Serially Diluted SP-PnF
Co~ting Solution Dose per Well Absorbance (,ug/ml) (g/well) PnF
Negative Control 0.0 0.047 + 0.004 ProNectin F at 10,ug/ml 1.0 x 10-5 0.683 + 0.017 SP-PnF at 10 ~g/ml 1.0 x 1o-5 0.724 + 0.015 SP-PnF at 1.0 ,ug/ml 1.0 x 10~ 0.741 + 0.023 SP-PnF at O. 1 ,ug/ml 1.0 x 10-7 0.731 + 0.032 Atta~k.~ of VERO Cells On Poly~ly~ Coated With DMA-PnF
In order to judge the c~...l.etenc~ of DMA-PnF with respect to surf~t~nt activity and cell ~tt~hm~nt activity, a cell ~tt~-hment assay was performed on a multi-well 20 polystyrene tissue culture plate with 96 wells. In this assay, ProNectin F was made up in 4.5 molar lithium perchlorate at 1.0 mg/ml and serially diluted with phosphate buffered saline to the final coating concentration of 10 ,ug/ml, and then applied to the first lane of 8 wells. The DMA-PnF was dissolved in deionized water at 1 mg/ml and diluted to the final coating concentrations of 10 ~g/ml, 1.0 ~cg/ml, and 0.10 ,ug/ml.
25 Each dilution was applied to one lane of 8 wells on the plate. Blocking, inoculation with cells, incubation, fixation, and st~ining with amido blue black dye were all conducted according to standard protocols. Relative cell numbers were estim~t~d spectrophotometrically at 495 nm. The results of this assay are reported in Table 8.

CA 0220~219 1997-0~-13 Wo 96/16168 Pcrtuss5ll29ss Table 8.
VERO Cell ~tt~rhmPnt On ProNectin~F And On Serially Diluted DMA-PnF
Co~ting Solution Dose per Well Absoll~ance (~g/ml) (g/well) PnF
NegativeControl 0.0 0.044 + 0.002 ProNectin F at 10 ~g/ml1.0 x 10-5 0.728 + 0.042 SP-PnF at 10 ,ug/ml 1.0 x 10-5 0.771 + 0.022 SP-PnF at 1.0 ,ug/ml 1.0 x 10~ 0.715 + 0.029 SP-PnF at 0.1 ~g/ml 1.0 x 10-7 0.652 + 0.031 The data show that HP-PnF retains its activity as both a surfactant and as a cell ~tt~rhm~nt surface motlifi~r. Furthermore, the hydroxypropylation does not cause any acute cytotoxicity. The hydroxypropylated polymer shows utility for coating polystyrene for purposes of m~mm~ n cell culture. The modification also makes it15 suitable for other purposes, such as deposition on polypropylene fibers.
It is evident from the data p~sented that the subject methods increase the watersolubility of highly repetitive, ordered proteins, without decreasing the protein's adhesive properties. After modification, the proteins can be solubilized in water, and used to coat plastic surfaces for biological purposes, elimin~ting the need for 20 solubilizing in toxic solutions.
All pllhlir,~tionc and patent applications mentioned in this spe~ific~tion are herein incGlyold~d by ~cr~;lu~ce to the same extent as if each individual publication or patent applir~ti- n was s~ifi~lly and individually indicated to be incorporated by reference.
The invention now being fully described, it will be al)palcnt to one of ordinary25 skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the appended claims.

Claims (26)

WHAT IS CLAIMED IS:

1. A method of preparing a water soluble protein from a water insoluble, at least partially crystalline, repetitive unit precursor protein comprising a naturally occuring amino acid having a reactive heteroatom containing functionality, said method comprising:
dissolving said precursor protein in an organic solvent, high salt concentrationaqueous solvent, or combination thereof, to provide a reaction solution;
adding to said reaction solution an organic reactant under conditions for reaction of said organic reactant with said functionality to retain said heteroatom and provide at least one polar additional heteroatom, whereby at least 1% of said amino acids are functionalized;
whereby said water soluble protein is produced.

2. A method according to Claim 1, wherein said solvent is an aqueous high ionic strength solution.

3. A method according to Claim 2, wherein said solution is at least 2 M in a lithium salt and said condition is a pH of at least 9.

4. A method according to Claim 3, wherein said organic reactant is an epoxide of from 2 to 5 carbon atoms.

5. A method according to Claim 1, wherein said repetitive unit is a fibroin repetitive unit.

6. A method of preparing a water soluble protein from a water insoluble, at least partially crystalline, fibroin repetitive unit precursor protein comprising serine or threonine as a member of said repetitive unit, said method comprising:
dissolving said precursor protein in a high salt concentration basic aqueous solvent to provide a reaction solution;

adding to said reaction solution an epoxide of from 2 to 5 carbon atoms, whereby at least 1% of said amino acids are functionalized to provide said water soluble protein.

7. A method according to Claim 6, wherein said aqueous solvent is at least 2 M in a lithium salt and has an hydroxide concentration of at least about 10mM.

8. A method according to Claim 6, wherein said precursor protein comprises intervening groups comprising a cell binding sequence.

9. A method of preparing a water soluble protein from a water insoluble, at least partially crystalline, repetitive unit precursor protein comprising serine or threonine in said repetitive unit, said method comprising:
dissolving said precursor protein in a basic high salt concentration aqueous solvent, to provide a reaction solution;
adding to said reaction solution an organic reactant under conditions for reaction of said organic reactant with said functionality to retain said heteroatom and provide at least one polar additional heteroatom functionality selected from the group consisting of hydroxyl, sulfonate, and ammonio, whereby at least 1% of said amino acids arefunctionalized;
whereby said water soluble protein is produced.

10. A method according to Claim 9, wherein said additional heteroatom functionality is hydroxyl and said reactant is an expoxide of from 2 to 4 carbon atoms.

11. A method according to Claim 9, wherein said additional heteroatom functionality is sulfonate and said reactant is a sultone of from 3 to 8 carbon atoms.

12. A method according to Claim 9, wherein said additional heteroatom functionality is ammonio of from 4 to 8 carbon atoms.

13. A water soluble repetitive unit protein compound of at least 6 kD, wherein said repetitive units are of from 3 to 30 amino acids, comprise at least one amino acid comprising a chemically reactive heteroatom containing functionality of which at least about 1% are bonded to a polar group substituted alkyl group of from 2 to 8 carbon atoms.

14. A protein compound according to Claim 13, wherein said repetitive units are of from about 4 to 10 amino acids and comprise serine or threonine, and said polar group is hydroxyl.

15. A protein compound according to Claim 13, wherein said polar group is ammonio.

16. A protein compound according to Claim 13, wherein said polar group is acidic.

17. A water soluble fibroin repetitive unit protein compound of at least 6 kD, said repetitive unit comprising a serine of which at least about 1% are bonded to a polar group substituted alkyl group of from 2 to 8 carbon atoms.

18. A protein compound according to Claim 17, wherein said polar group is selected from the group consisting of hydroxyl, sulfonato and ammonio.

19. A protein compound according to Claim 17, wherein said repetitive units have an intervening sequence comprising a physiologically active sequence.

20. A protein compound according to Claim 19, wherein said physiologically acitve sequence comprises RGDS.

21. A water soluble protein compound of at least about 10 kD comprising repetitive units of the sequence GAGAGS and having an intervening sequence comprising RGDS, having at least about 1% of the serine groups alkylated with a polar group substituted alkyl group of from 2 to 8 carbon atoms, wherein said polar group is selected from the group consisting of hydroxyl, sulfonato, and ammonio.

22. A solid substrate comprising a coating of a protein compound according to Claim 13.

23. A solid substrate comprising a coating of a protein compound according to Claim 13.

24. A solid substrate comprising a coating of a protein compound according to Claim 21.

25. A solid substrate comprising a coating of a protein compound according to Claim 24, wherein said polar group is hydroxyl.

26. An aqueous solution having less than about 1 M salt concentration and at least 0.01 weight % of a protein compound according to Claim 13.