title: Chemo-enzymatic synthesis of polyhydroxyalkanoate (PHA) incorporating 2-hydroxybutyrate by wild-type class I PHA synthase from Ralstonia eutropha.
abstract: A previously established improved two-phase reaction system has been applied to analyze the substrate specificities and polymerization activities of polyhydroxyalkanoate (PHA) synthases. We first analyzed the substrate specificity of propionate coenzyme A (CoA) transferase and found that 2-hydroxybutyrate (2HB) was converted into its CoA derivative. Then, the synthesis of PHA incorporating 2HB was achieved by a wild-type class I PHA synthase from Ralstonia eutropha. The PHA synthase stereoselectively polymerized (R)-2HB, and the maximal molar ratio of 2HB in the polymer was 9 mol%. The yields and the molecular weights of the products were decreased with the increase of the (R)-2HB concentration in the reaction mixture. The weight-average molecular weight of the polymer incorporating 9 mol% 2HB was 1.00 × 10(5), and a unimodal peak with polydispersity of 3.1 was observed in the GPC chart. Thermal properties of the polymer incorporating 9 mol% 2HB were analyzed by DSC and TG-DTA. T (g), T (m), and T (d) (10%) were observed at -1.1°C, 158.8°C, and 252.7°C, respectively. In general, major components of PHAs are 3-hydroxyalkanoates, and only engineered class II PHA synthases have been reported as enzymes having the ability to polymerize HA with the hydroxyl group at C2 position. Thus, this is the first report to demonstrate that wild-type class I PHA synthase was able to polymerize 2HB.
authors.affiliation: Division of Biotechnology and Macromolecular Chemistry, Graduate School of Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo, 060-8628, Japan.
authors.forename: Xuerong
authors.initials: X
authors.lastname: Han
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Satoh
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Satoh
authors.forename: Ken'ichiro
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Toyoji
authors.initials: T
authors.lastname: Kakuchi
authors.forename: Seiichi
authors.initials: S
authors.lastname: Taguchi
authors.forename: Tohru
authors.initials: T
authors.lastname: Dairi
authors.forename: Masanobu
authors.initials: M
authors.lastname: Munekata
authors.forename: Kenji
authors.initials: K
authors.lastname: Tajima
mesh_terms: D000217:Acyltransferases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D003065:Coenzyme A / Q000378:metabolism; D020118:Cupriavidus necator / Q000201:enzymology*; D006885:Hydroxybutyrates / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D054813:Polyhydroxyalkanoates / Q000737:chemistry / Q000378:metabolism*; D011422:Propionates / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D006885:Hydroxybutyrates; D054813:Polyhydroxyalkanoates; D011422:Propionates; D000217:Acyltransferases; C077225:poly(3-hydroxyalkanoic acid) synthase; D003065:Coenzyme A