Polyhydroxyalkanoate (PHA) biosynthesis in Thermus thermophilus: Purification and biochemical properties of PHA synthase |
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Authors: | Pantazaki Anastasia A. Tambaka Maria G. Langlois Valerie Guerin Philippe Kyriakidis Dimitrios A. |
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Affiliation: | (1) Laboratory of Biochemistry, Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki, 54006, Greece;(2) Laboratoire de la Recherche sur les Polymères, CNRS, 2-8 rue Henry Dunant, F-94320 Thiais, France |
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Abstract: | The biosynthesis of polyhydroxyalkanoates (PHAs) was studied, for the first time, in the thermophilic bacterium Thermus thermophilus. Using sodium gluconate (1.5% w/v) or sodium octanoate (10 mM) as sole carbon sources, PHAs were accumulated to approximately 35 or 40% of the cellular dry weight, respectively. Gas chromatographic analysis of PHA isolated from gluconate-grown cells showed that the polyester (Mw: 480,000 g.mol–1) was mainly composed of 3-hydroxydecanoate (3HD) with a molar fraction of 64%. In addition, 3-hydroxyoctanoate (3HO), 3-hydroxyvalerate (3HV) and 3-hydroxybutyrate (3HB) occurred as constituents. In contrast, the polyester (Mw: 391,000 g mol–1) from octanoate-grown cells was composed of 24.5 mol% 3HB, 5.4 mol% 3HO, 12.3 mol% 3-hydroxynonanoate (3HN), 14.6 mol% 3HD, 35.4 mol% 3-hydroxyundecanoate (3HUD) and 7.8 mol% 3-hydroxydodecanoate (3HDD). Activities of PHA synthase, a -ketothiolase and an NADPH-dependent reductase were detected in the soluble cytosolic fraction obtained from gluconate-grown cells of T. thermophilus. The soluble PHA synthase was purified 4271-fold with 8.5% recovery from gluconate-grown cells, presenting a Km of 0.25 mM for 3HB-CoA. The optimal temperature of PHA synthase activity was about 70°C and acts optimally at pH near 7.3. PHA synthase activity was inhibited 50% with 25 M CoA and lost all of its activity when it was treated with alkaline phosphatase. PHA synthase, in contrary to other reported PHA synthases did not exhibit a lag phase on its kinetics, when low concentration of the enzyme was used. Incubation of PHA synthase with 1 mM N-ethyl-maleimide inhibits the enzyme 56%, indicating that cysteine might be involved in the catalytic site of the enzyme. Acetyl phosphate (10 mM) activated both the native and the dephosphorylated enzyme. A major protein (55 kDa) was detected by SDS-PAGE. When a partially purified preparation was analyzed on native PAGE the major band exhibiting PHA synthase activity was eluted from the gel and analyzed further on SDS-PAGE, presenting the first purification of a PHA synthase from a thermophilic microorganism. |
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Keywords: | polyhydroxyalkanoic acids (PHAs) synthase /content/k0kk604111hj2214/xxlarge946.gif" alt=" beta" align=" MIDDLE" BORDER=" 0" >-ketothiolase NADPH-dependent reductase Thermus thermophilus |
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