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To elucidate the effects of uniformity of molecular architecture on gel properties, a protein polymer based on the elastin-mimetic repeat sequence (Val-Pro-Gly-Val-Gly) 4 (Val-Pro-Gly-Lys-Gly), 1 ( Lys-25 ), was synthesized using genetic engineering and microbial protein expression. The regularly placed lysine residues in poly( Lys-25 ) underwent selective reaction with electrophilic cross-linkers under mild conditions in either dimethyl sulfoxide or aqueous phosphate buffer to afford solvent-swollen networks. Chemical derivatization and spectroscopic investigations of the cross-linking reaction indicated that approximately 85% of the lysine residues reacted with the cross-linker. The protein hydrogel exhibited reversible, temperature-dependent expansion and contraction with an estimated midpoint temperature for the phase transition at 35 °C. Scanning electron microscopy (SEM) investigations indicated profound differences in morphology between protein gels prepared in organic vs aqueous solution.
McMillan et al. (Thu,) studied this question.