(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 PhaC subunit of a heterodimeric form of polyhydroxyalkanoic acid (PHA) synthase. Excepting the PhaC of Bacillus megaterium (which needs PhaR is not an a/b hydrolase), all members require PhaE (IPR010123 PhaE is not an a/b hydrolase) subunit for activity and are designated class III. (PhaC of Bacillus associated to PhaR are designed Class IV PHA_synth_IV but are not separated here) . This enzyme builds ester polymers for carbon and energy storage that accumulate in inclusions, and both this enzyme and the depolymerase associate with the inclusions. Class III enzymes polymerise short-chain-length hydroxyalkanoates. 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), IPR010125 (Poly(R)-hydroxyalkanoic acid synthase, class III, PhaC subunit PHA_synth_III_C)
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: PhaC and PhaR are required for polyhydroxyalkanoic acid synthase activity in Bacillus megaterium McCool GJ, Cannon MC Ref: Journal of Bacteriology, 183:4235, 2001 : PubMed
Polyhydroxyalkanoic acids (PHAs) are a class of polyesters stored in inclusion bodies and found in many bacteria and in some archaea. The terminal step in the synthesis of PHA is catalyzed by PHA synthase. Genes encoding this enzyme have been cloned, and the primary sequence of the protein, PhaC, is deduced from the nucleotide sequences of more than 30 organisms. PHA synthases are grouped into three classes based on substrate range, molecular mass, and whether or not there is a requirement for phaE in addition to the phaC gene product. Here we report the results of an analysis of a PHA synthase that does not fit any of the described classes. This novel PHA synthase from Bacillus megaterium required PhaC (PhaC(Bm)) and PhaR (PhaR(Bm)) for activity in vivo and in vitro. PhaC(Bm) showed greatest similarity to the PhaCs of class III in both size and sequence. Unlike those in class III, the 40-kDa PhaE was not required, and furthermore, the 22-kDa PhaR(Bm) had no obvious homology to PhaE. Previously we showed that PhaC(Bm), and here we show that PhaR(Bm), is localized to inclusion bodies in living cells. We show that two forms of PHA synthase exist, an active form in PHA-accumulating cells and an inactive form in nonaccumulating cells. PhaC was constitutively produced in both cell types but was more susceptible to protease degradation in the latter type. Our data show that the role of PhaR is posttranscriptional and that it functions directly or indirectly with PhaC(Bm) to produce an active PHA synthase.
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)