Methylated mono- and di(ethylene glycol)-functionalized beta-sheet forming polypeptides

We have synthesized methylated mono- and di(ethylene glycol)-functionalized polymers of L-serine and L-cysteine that adopt beta-sheet conformations in the solid state: poly(O-(2-(2-methoxyethoxy)ethyl)-L-serine), poly(1); poly(O-(2-(methoxy)ethyl)-L-serine), poly(2); and poly(S-(2-(2-methoxyethoxy)ethoxy)carbonyl-L-cysteine), poly(3). Of these three polymers, only poly(1) was found to be highly soluble in water independent of pH. Circular dichroism analysis of poly(1) in water or trifluoroethanol at 25 degrees C revealed that it is in a random conformation, which was unperturbed by changes in pH, buffer, or temperature. However, addition of methanol or acetonitrile to aqueous solutions of poly(1) resulted in a transition to the beta-sheet conformation, as found in the solid state. The polymers were synthesized by transition metal catalyzed polymerization of amino acid-N-carboxyanhydrides, prepared from the functionalized amino acids and represent a new class of readily processable beta-sheet forming polypeptides.