EC 2.3.1.304     
Accepted name: poly[(R)-3-hydroxyalkanoate] polymerase
Reaction: (3R)-3-hydroxyacyl-CoA + poly[(R)-3-hydroxyalkanoate]n = CoA + poly[(R)-3-hydroxyalkanoate]n+1
Other name(s): PHA synthase; phaC (gene name); PhaE
Systematic name: poly(R)-3-hydroxyalkanoate (3R)-3-hydroxyacyltransferase
Comments: This is the key enzyme in the biosynthesis of polyhydroxyalkanoates (PHA), linear polyesters produced by bacteria as a means of carbon and energy storage [6]. The enzyme catalyses the stereoselective, covalent linkage of (3R)-3-hydroxyacyl-CoA thioesters in a transesterification reaction with concomitant release of coenzyme A. The growing polymer is attached to a conserved active site L-cysteine residue. Three types of PHA synthases have been proposed based on their substrate specificity and enzyme structure. Type I and type III synthases preferentially polymerize short chain hydroxyalkanoate monomers containing 3-5 carbon atoms [1,2]. The difference between these two types is that type I synthases are composed of only a single subunit (PhaC), whereas type III synthases are composed of two different subunits, PhaC and PhaE [3,5]. Type II synthases are also composed of a single subunit (PhaC), but preferentially polymerize monomers containing more than 5 carbon atoms [4].
References:
1.  Anderson, A.J., Haywood, G.W. and Dawes, E.A. Biosynthesis and composition of bacterial poly(hydroxyalkanoates). Int. J. Biol. Macromol. 12 (1990) 102–105. [PMID: 2078525]
2.  Liebergesell, M., Sonomoto, K., Madkour, M., Mayer, F. and Steinbuchel, A. Purification and characterization of the poly(hydroxyalkanoic acid) synthase from Chromatium vinosum and localization of the enzyme at the surface of poly(hydroxyalkanoic acid) granules. Eur. J. Biochem. 226 (1994) 71–80. [PMID: 7957260]
3.  Muh, U., Sinskey, A.J., Kirby, D.P., Lane, W.S. and Stubbe, J. PHA synthase from Chromatium vinosum: cysteine 149 is involved in covalent catalysis. Biochemistry 38 (1999) 826–837. [PMID: 9888824]
4.  Ren, Q., De Roo, G., Kessler, B. and Witholt, B. Recovery of active medium-chain-length-poly-3-hydroxyalkanoate polymerase from inactive inclusion bodies using ion-exchange resin. Biochem. J. 349 (2000) 599–604. [PMID: 10880359]
5.  Jia, Y., Yuan, W., Wodzinska, J., Park, C., Sinskey, A.J. and Stubbe, J. Mechanistic studies on class I polyhydroxybutyrate (PHB) synthase from Ralstonia eutropha: class I and III synthases share a similar catalytic mechanism. Biochemistry 40 (2001) 1011–1019. [PMID: 11170423]
6.  Zou, H., Shi, M., Zhang, T., Li, L., Li, L. and Xian, M. Natural and engineered polyhydroxyalkanoate (PHA) synthase: key enzyme in biopolyester production. Appl. Microbiol. Biotechnol. 101 (2017) 7417–7426. [PMID: 28884324]
[EC 2.3.1.304 created 2021]