Genetic Engineering of Structural Protein Polymers

Abstract

Genetic and protein engineering are components of a new polymer chemistry that 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 properties of these materials have been attributed to the presence of short repeating oligopeptide sequences contained in the proteins, fibroin, and elastin. We have produced homoblock protein polymers consisting exclusively of silk-like crystalline blocks and elastin-like flexible blocks. We have demonstrated that each homoblock polymer as produced by microbial fermentation exhibits measurable properties of crystallinity and elasticity. Additionally, we have produced alternating block 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 varies with the amount of crystalline block interruptions. The production of fiber materials with custom-engineered mechanical properties is a potential outcome of this technology.

Peptide-Based Polymer Therapeutics

“…To produce larger sequences that will encode for repetitive polypeptides of high Mw, these chemically synthesised short DNA sequences must be assembled. There are different methods to gather the small sequences such as concatenation of oligonucleotides [54], recursive directional ligation (RDL) [55], and mutagenesis or amplification of existing gene segments using polymerase chain reaction (PCR) [56]. However, it is not within the scope of this review to discuss in detail all the methods, please check [54][55][56] for further details.…”

Peptide-based biopolymers in biomedicine and biotechnology

“…Many synthetic genes encoding B. mori silk-like sequences have been cloned and expressed in E. coli. A six amino acid repeat [GAGAGS] controls crystallinity in films and fibers [50], and repeats such as [(AG) 3 PEG] [51] and [(AG) 3 EG] [52] have been used in efforts to control crystalline order in protein-based materials.…”

“…They also showed that the addition of elastin-like blocks within the SLPs to make silk-elastin-like proteins (SELPs) further disrupts the crystalline structure. While SLPs are generally insoluble in aqueous solution, the ELP blocks influence the molecular chain properties of the protein so that the SELPs are water soluble [50]. This is an important property, as water solubility is essential for the manufacturing, purifying, and processing of silk-like biopolymers.…”

“…The concatemerization method and RDL are both designed to generate repetitive DNA sequences [50]. Both ELP and silk genes are candidates for these methods of gene design, as they consist of pentamer repeat units [57,58].…”

“…However, silk undergoes strong intramolecular hydrogen bonding that leads to rapid crystallization and can complicate its use for injection-based applications [53,167]. One route to increasing its solubility is the incorporation of peptide sequences from other proteins, such as elastin, that disrupt β-sheet formation [50]. Silk elastin-like polypeptides (SELPs) are chimeric proteins designed to retain the mechanical properties of silk, while incorporating the high solubility and environmental sensitivity of ELPs [139,161,168].…”