Polyester PHA Synthases are the Key Enzymes

Exhaustive examination of the primary structures of 88 PHA synthases have shown that these enzymes from different bacteria display strong similarity ranging from 8% to 96% identity. Six conserved blocks were identified on the basis of conserved amino acid sequence regions, whereas the N-terminal region (about 100 amino acids relative to class I polyester synthases) is highly variable [37]. 

The first PHB synthase from an extremely halophilic archaebacterium was identified and characterized by Hezayen etal. [4], representing presumably a new class 

There are no current structural data of polyester synthases. The secondary structure content was inferred by predictions implementing the multiple alignments of synthases. The use of JPred indicated that polyester synthases are mostly composed of variable loops (49.7%) and a-helical (39.9%) secondary structures, whereas only 10.4% were proposed as P-sheet secondary structures [38]. However, circular dichroism spectroscopy suggested that the class II synthase from P. aeruginosa is comprised of the secondary structures 10% a-helix, 50% P-sheet, and 40% random coil [39]. 

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