Designer enzyme for green materials innovation: Lactate-polymerizing enzyme as a key catalyst

Complete sequence randomness of lactate-based copolymers (LAHBs) with varied lactate monomer fractions employing a series of propionyl-CoA transferases

Previously, we biosynthesized an evolved version of a bio-based polylactide (PLA) on microbial platforms using our engineered lactate-polymerizing enzyme (LPE). This lactate (LA)-based copolyester, LAHB, has advantages over PLA, including improved flexibility and biodegradability, and its properties can be regulated through the LA fraction. To expand the LA-incorporation capacity and improve polymer properties, in the state of in vivo LAHB production, propionyl-CoA transferases (PCTs) that exhibited enhanced production of LA-CoA than the conventional PCTs were selected. Here, the present study has demonstrated that the LA fraction of LAHB could be altered using various PCTs. Enhanced PCT performance was achieved by balancing polymer production and cell growth. Both events are governed by the use of acetyl-CoA, a commonly shared key metabolite. This could be attributed to the different reactivities of individual PCTs towards acetyl-CoA, which serves both as a CoA donor and a leading compound in the TCA cycle. Interestingly, we found complete sequence randomness in the LAHB copolymers, independent of the LA fraction. The mechanism of LA fraction-independent sequence randomness is discussed. This new PCT-based strategy synergistically combines with the evolution of LPE to advance the LAHB project, and enables us to perform advanced applications other than LAHB production utilizing CoA-linked substrates.

Synthetic biology strategies for improving microbial synthesis of "green" biopolymers

Polysaccharide-based biopolymers have many material properties relevant to industrial and medical uses, including as drug delivery agents, wound-healing adhesives, and food additives and stabilizers. Traditionally, polysaccharides are obtained from natural sources. Microbial synthesis offers an attractive alternative for sustainable production of tailored biopolymers. Here, we review synthetic biology strategies for select "green" biopolymers: cellulose, alginate, chitin, chitosan, and hyaluronan. Microbial production pathways, opportunities for pathway yield improvements, and advances in microbial engineering of biopolymers in various hosts are discussed. Taken together, microbial engineering has expanded the repertoire of green biological chemistry by increasing the diversity of biobased materials.