Genetic Production of Synthetic Protein Polymers

Abstract

A goal of polymer chemistry is to control the final properties of a processed material by controlling the chemistry and physics of the polymer chain. Since the final formulated materials' properties are a complex function of chemical and physical interactions at both the micro and macro scales, it would be desirable to influence those interactions at the level of the molecular chemistry of the chain. However, in order to affect those macromolecular associations that occur via chemical functionalities separated over long distances, a chemistry is needed that can specify not only variability in chemical composition along the chain but can also specify the positions at which this chemical variability must occur over the entire length of the chain—several hundred nanometers.Protein-based materials in nature are formulated from protein chains which have evolved chemical compositions that through the specific sequence of their amino acid monomer constituents can result in diverse materials such as ultrahigh strength fibers, silks and collagens, and soft, ultradurable elastomers, elastin. As described in the article by Kaplan in this issue, the fundamental six amino acid repeat of the crystalline fraction of Bombyx mori silk fibroin is composed of essentially three amino acids, glycine (G), alanine (A), and serine (S), in a 3:2:1 ratio. The strength of the fiber is derived from these crystallized peptide blocks. They are positioned to a great extent as tandem repeats of the sequence GAGAGS.