Applied Microbiology and Biotechnology

, Volume 103, Issue 3, pp 1131–1141 | Cite as

PHA synthase (PhaC): interpreting the functions of bioplastic-producing enzyme from a structural perspective

  • Min Fey Chek
  • Ayaka Hiroe
  • Toshio Hakoshima
  • Kumar SudeshEmail author
  • Seiichi TaguchiEmail author


Polyhydroxyalkanoates (PHAs) are biopolymers synthesized by a wide range of bacteria, which serve as a promising candidate in replacing some conventional petrochemical-based plastics. PHA synthase (PhaC) is the key enzyme in the polymerization of PHA, and the crystal structures were successfully determined using the catalytic domain of PhaC from Cupriavidus necator (PhaCCn-CAT) and Chromobacterium sp. USM2 (PhaCCs-CAT). Here, we review the beneficial mutations discovered in PhaCs from a structural perspective. The structural comparison of the residues involved in beneficial mutation reveals that the residues are near to the catalytic triad, but not inside the catalytic pocket. For instance, Ala510 of PhaCCn is near catalytic His508 and may be involved in the open-close regulation, which presumably play an important role in substrate specificity and activity. In the class II PhaC1 from Pseudomonas sp. 61-3 (PhaC1Ps), Ser325 stabilizes the catalytic cysteine through hydrogen bonding. Another residue, Gln508 of PhaC1Ps is located in a conserved hydrophobic pocket which is next to the catalytic Asp and His. A class I, II-conserved Phe420 of PhaCCn is one of the residues involved in dimerization and its mutation to serine greatly reduced the lag phase. The current structural analysis shows that the Phe362 and Phe518 of PhaC from Aeromonas caviae (PhaCAc) are assisting the dimer formation and maintaining the integrity of the core beta-sheet, respectively. The structure-function relationship of PhaCs discussed in this review will serve as valuable reference for future protein engineering works to enhance the performance of PhaCs and to produce novel biopolymers.


Beneficial mutation Dimerization Evolutionary engineering Open-closed form Polyhydroxyalkanoate synthase Substrate specificity Tertiary structure 


Funding information

This work is supported by Research University Grant (RUI) from the Universiti Sains Malaysia (1001/PBIOLOGI/8011060 to K.S.), JST A-STEP Grant (29A1027 to T.H.) and JST CREST grant (JPMJCR12B4 to S.T.).

Compliance with ethical standards

This article does not contain any studies with human participants or animals performed by any of the authors.

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Structural Biology LaboratoryNara Institute of Science and TechnologyIkomaJapan
  2. 2.Department of Chemistry for Life Sciences and Agriculture, Faculty of Life SciencesTokyo University of AgricultureSetagayaJapan
  3. 3.CREST, JSTKawaguchiJapan
  4. 4.School of Biological SciencesUniversiti Sains MalaysiaGelugorMalaysia

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