Natural and engineered polyhydroxyalkanoate (PHA) synthase: key enzyme in biopolyester production

Abstract

With the finite supply of petroleum and increasing concern with environmental issues associated with their harvest and processing, the development of more eco-friendly, sustainable alternative biopolymers that can effectively fill the role of petro-polymers has become a major focus. Polyhydroxyalkanoate (PHA) can be naturally produced by many species of bacteria and the PHA synthase is believed to be key enzyme in this natural pathway. Natural PHA synthases are diverse and can affect the properties of the produced PHAs, such as monomer composition, molecular weights, and material properties. Moreover, recent studies have led to major advances in the searching of PHA synthases that display specific properties, as well as engineering efforts that offer more efficient PHA synthases, increased PHA compound production, or even novel biopolyesters which cannot be naturally produced. In this article, we review the updated information of natural PHA synthases and their engineering strategies for improved performance in polyester production. We also speculate future trends on the development of robust PHA synthases and their application in biopolyester production.

Contribution of protein synthesis depression to poly-β-hydroxybutyrate accumulation in Synechocystis sp. PCC 6803 under nutrient-starved conditions

“…The bacterial genes for PHA synthesis includes phaA for ß-ketothiolase that catalyzes the condensation of two molecules of acetyl-CoA for the synthesis of acetoacetyl-CoA, phaB for NADPH-dependent acetoacetyl-CoA reductase that synthesizes the monomeric precursor, hydroxyalkanoate, and the gene(s) for PHA synthase that polymerizes the precursor 11 . PHB synthases can be divided into four classes according to the primary sequences of the subunit proteins: Classe I and II PHA synthases are encoded by the genes for single subunits, phaC , and phaC1 or phaC2 , respectively, while class III and IV PHA synthases are encoded by the genes for heterodimer subunits, phaC and phaE , and phaC and phaR , respectively 12 . It is generally accepted that class I, III, and IV PHA synthases predominantly utilize short-chain length monomers (C3-C5), in contrast, class II PHA synthase having a preference for medium-chain length monomers (C6-C14, 12 ).…”

“…PHB synthases can be divided into four classes according to the primary sequences of the subunit proteins: Classe I and II PHA synthases are encoded by the genes for single subunits, phaC , and phaC1 or phaC2 , respectively, while class III and IV PHA synthases are encoded by the genes for heterodimer subunits, phaC and phaE , and phaC and phaR , respectively 12 . It is generally accepted that class I, III, and IV PHA synthases predominantly utilize short-chain length monomers (C3-C5), in contrast, class II PHA synthase having a preference for medium-chain length monomers (C6-C14, 12 ).…”

Role of PhaC Type I and Type II Enzymes during PHA Biosynthesis

“…Many authors described mutations in amino acids positioned in various domains of different PHA synthases, most often finding a decrease in production of mcl-PHA and higher synthesis of scl-PHA. Beneficial effects of mutagenesis studies of Glu 130 and Ser 477 have been described [38,39,40,41]. For instance, the E 130 D substitution and S 477 X mutation in type II PHA synthase showed an enhancement of PHA production and alteration of polymer molecular weight.…”

Increased Production and Molecular Weight of Artificial Polyhydroxyalkanoate Poly(2-hydroxybutyrate) Above the Glass Transition Temperature Threshold

“…The physical properties of polymer materials mainly depend on the structures of their monomeric constituents and their molecular weight. The variety of monomer constituents in a polymer is determined largely by the substrate specificity of a PHA synthase (Zou et al, 2017). In contrast, the factors jointly influence the molecular weight of PHA.…”

“…Naturally occurring PHAs are typically composed of 3-hydroxyalkanoates, and the substrate specificity of the PHA synthases influence their carbon numbers (Zou et al, 2017). The biosynthesis of poly(2-hydroxypropionate) (polylactate or PLA), which is structurally similar to PHAs, has attracted the attention of researchers due to its superior properties.…”