Structure of polyhydroxyalkanoate (PHA) synthase PhaC from Chromobacterium sp. USM2, producing biodegradable plastics

Area of Science:

• Biochemistry
• Structural Biology
• Polymer Science

Background:

• Polyhydroxyalkanoates (PHAs) are biodegradable bioplastics with potential to replace petroleum-based plastics.
• Limited three-dimensional structural information of PHA synthase (PhaC) hinders a full understanding of its catalytic mechanism.
• Previous studies lack detailed structural insights into different conformational states of PhaC.

Purpose of the Study:

• To determine the high-resolution crystal structure of the catalytic domain of PHA synthase from Chromobacterium sp. USM2 (PhaC_Cs-CAT).
• To elucidate the structural differences between PhaC_Cs-CAT and other reported PhaC structures.
• To gain insights into the conformational changes and dimerization of PhaC relevant to its catalytic activity.

Main Methods:

• High-resolution X-ray crystallography was employed to determine the three-dimensional structure of PhaC_Cs-CAT.
• Structural analysis involved characterizing the α/β hydrolase fold, active site, and subdomain arrangements.
• Comparative structural analysis was performed with the catalytic domain from Cupriavidus necator (PhaC_Cn-CAT).

Main Results:

• The crystal structure of PhaC_Cs-CAT reveals an α/β hydrolase fold with distinct α/β core and CAP subdomains.
• PhaC_Cs-CAT adopts a closed conformation with the active site cavity filled with water and covered by a disordered CAP subdomain.
• PhaC_Cs-CAT forms a unique face-to-face dimer mediated by CAP subdomains, differing from the PhaC_Cn-CAT dimer structure.

Conclusions:

• The closed conformation of PhaC_Cs-CAT provides new structural insights into PHA synthase.
• The distinct dimeric arrangement and CAP subdomain structure suggest a role in regulating substrate entry and product egress.
• Conformational changes in the CAP subdomain and dimer rearrangement are likely crucial for PhaC's catalytic cycle.