Chemical and biosynthetic approaches to the production of novel polypeptide materials

Three approaches to the synthesis of the repetitive copolypeptide [(GlyAla)3-GlyProGlu]n (1) are described. Direct chemical synthesis of 1 via classical solution methods required 18 steps and afforded a polydisperse product with an average molecular weight of less than 10,000. Two alternative genetic strategies were also explored. In the first, chemically synthesized DNA oligomers were self-ligated to produce a population of multimers, which were fitted with translational start and stop signals and inserted into an expression plasmid containing the lambda PL promoter and a synthetic ribosome binding site. Transformation of E. coli led to the isolation of a stable recombinant plasmid carrying an insert encoding 12 repeats of sequence 1. Attempts to identify polypeptide 1 after induction of transformed cultures were unsuccessful. A second strategy, generating a tripartite derivative of sequence 1 carrying short N- and C-terminal extensions, afforded excellent yields of product. The relative merits of chemical and genetic approaches to repetitive polypeptide materials are discussed.