The Genetic Production of Synthetic Crystalline Protein Polymers

Abstract

Genetic and protein engineering are components of a new polymer chemistry which provide the tools for producing macromolecular polyamide copolymers of diversity and precision far beyond the current capabilities of synthetic polymer chemistry. The genetic machinery allows molecular control of chemical and physical chain properties. Nature utilizes this control to formulate protein polymers into materials with extraordinary mechanical properties such as the strength and toughness of silk and the elasticity and resilience of mammalian elastin. The protein chains which make up these fibers consist of extensive repeating oligopeptide sequences. By producing synthetically designed protein chains containing many tandem repeats of only one repetitive sequence block (homoblock polymers), we are able to evaluate the inherent contribution of each repeat to the overall material properties. Using biotechnology, we produced homoblock protein polymers consisting exclusively of silklike crystalline blocks in quantities sufficient for material evaluation studies (10–100 grams). Silk-like homoblock polymers, as produced by microbial fermentation, exhibited measurable crystallinity both in solution and in solid state. The chain properties of the homoblock polymer were changed by adding blocks of amino acids designed to contribute different structural or functional properties. We produced alternating copolymers of various amounts of silk-like and elastin-like blocks ranging from a ratio of 1:4 to 2:1, respectively. The crystallinity of each copolymer varied with the extent of crystalline block interruption. The substitution of the elastin block with one containing the amino acids from human fibronectin responsible for mammalian cell attachment, produced a highly active silk-like copolymer with biological activity. The ability to specifically engineer the mechanical and functional properties of a fiber material is a potential outcome of this technology.