(The family Pha_synthase was split in four families (PHA_synth_I, PHA_synth_II, PHA_synth_III, PhaC_cen_dom ) according to Interpro and Tigrpfam. PhaC_cen_dom groups enzyme with the central domain but not the class I,II,III domains)This entry represents the central domain of the bacterial poly-beta-hydroxybutyrate polymerase (PhaC). Polyhydroxyalkanoic acids (PHAs) are carbon and energy reserve polymers produced in some bacteria when carbon sources are plentiful and another nutrient, such as nitrogen, phosphate, oxygen, or sulphur, becomes limiting. PHAs composed of monomeric units ranging from 3 to 14 carbons exist in nature. When the carbon source is exhausted, PHA is utilised by the bacterium. PhaC links D-(-)-3-hydroxybutyrl-CoA to an existing PHA molecule by the formation of an ester bond. Poly-beta-hydroxybutyrate polymerase (PhaC) N-terminus. This entry represents the central domain of the bacterial poly-beta-hydroxybutyrate polymerase (PhaC). Polyhydroxyalkanoic acids (PHAs) are carbon and energy reserve polymers produced in some bacteria when carbon sources are plentiful and another nutrient, such as nitrogen, phosphate, oxygen, or sulphur, becomes limiting. PHAs composed of monomeric units ranging from 3 to 14 carbons exist in nature. When the carbon source is exhausted, PHA is utilised by the bacterium. PhaC links D-(-)-3-hydroxybutyrl-CoA to an existing PHA molecule by the formation of an ester bond PHA_synth_I TIGR01838 PHA_synth_II TIGR01839. The nucleophilic residue of the catalytic triad is a cysteine (with exceptions)
Database
Sequences
Interpro
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IPR010941 (PhaC_cen_dom Poly-beta-hydroxybutyrate polymerase, central domain)
Polyhydroxyalkanoates (PHAs) are biopolyesters composed of hydroxy fatty acids, which represent a complex class of storage polyesters. They are synthesized by a wide range of different Gram-positive and Gram-negative bacteria, as well as by some Archaea, and are deposited as insoluble cytoplasmic inclusions. Polyester synthases are the key enzymes of polyester biosynthesis and catalyse the conversion of (R)-hydroxyacyl-CoA thioesters to polyesters with the concomitant release of CoA. These soluble enzymes turn into amphipathic enzymes upon covalent catalysis of polyester-chain formation. A self-assembly process is initiated resulting in the formation of insoluble cytoplasmic inclusions with a phospholipid monolayer and covalently attached polyester synthases at the surface. Surface-attached polyester synthases show a marked increase in enzyme activity. These polyester synthases have only recently been biochemically characterized. An overview of these recent findings is provided. At present, 59 polyester synthase structural genes from 45 different bacteria have been cloned and the nucleotide sequences have been obtained. The multiple alignment of the primary structures of these polyester synthases show an overall identity of 8-96% with only eight strictly conserved amino acid residues. Polyester synthases can been assigned to four classes based on their substrate specificity and subunit composition. The current knowledge on the organization of the polyester synthase genes, and other genes encoding proteins related to PHA metabolism, is compiled. In addition, the primary structures of the 59 PHA synthases are aligned and analysed with respect to highly conserved amino acids, and biochemical features of polyester synthases are described. The proposed catalytic mechanism based on similarities to alpha/beta-hydrolases and mutational analysis is discussed. Different threading algorithms suggest that polyester synthases belong to the alpha/beta-hydrolase superfamily, with a conserved cysteine residue as catalytic nucleophile. This review provides a survey of the known biochemical features of these unique enzymes and their proposed catalytic mechanism.
Title: Cloning, molecular analysis, and expression of the polyhydroxyalkanoic acid synthase (phaC) gene from Chromobacterium violaceum Kolibachuk D, Miller A, Dennis D Ref: Applied Environmental Microbiology, 65:3561, 1999 : PubMed
The polyhydroxyalkanoic acid synthase gene from Chromobacterium violaceum (phaC(Cv)) was cloned and characterized. A 6.3-kb BamHI fragment was found to contain both phaC(Cv) and the polyhydroxyalkanoic acid (PHA)-specific 3-ketothiolase (phaA(Cv)). Escherichia coli strains harboring this fragment produced significant levels of PHA synthase and 3-ketothiolase, as judged by their activities. While C. violaceum accumulated poly(3-hydroxybutyrate) or poly(3-hydroxybutyrate-co-3-hydroxyvalerate) when grown on a fatty acid carbon source, Klebsiella aerogenes and Ralstonia eutropha (formerly Alcaligenes eutrophus), harboring phaC(Cv), accumulated the above-mentioned polymers and, additionally, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) when even-chain-length fatty acids were utilized as the carbon source. This finding suggests that the metabolic environments of these organisms are sufficiently different to alter the product range of the C. violaceum PHA synthase. Neither recombinant E. coli nor recombinant Pseudomonas putida harboring phaC(Cv) accumulated significant levels of PHA. Sequence analysis of the phaC(Cv) product shows homology with several PHA synthases, most notably a 48% identity with that of Alcaligenes latus (GenBank accession no. AAD10274).
