Polyhydroxyalkanoate (PHA) is a promising candidate for use as an alternative bioplastic to replace petroleum-based plastics. Our understanding of PHA synthase PhaC is poor due to the paucity of available three-dimensional structural information. Here we present a high-resolution crystal structure of the catalytic domain of PhaC from Chromobacterium sp. USM2, PhaC Cs -CAT. The structure shows that PhaC Cs -CAT forms an α/β hydrolase fold comprising α/β core and CAP subdomains. The active site containing Cys291, Asp447 and His477 is located at the bottom of the cavity, which is filled with water molecules and is covered by the partly disordered CAP subdomain. We designated our structure as the closed form, which is distinct from the recently reported catalytic domain from Cupriavidus necator (PhaC Cn -CAT). Structural comparison showed PhaC Cn -CAT adopting a partially open form maintaining a narrow substrate access channel to the active site, but no product egress. PhaC Cs -CAT forms a face-to-face dimer mediated by the CAP subdomains. This arrangement of the dimer is also distinct from that of the PhaC Cn -CAT dimer. These findings suggest that the CAP subdomain should undergo a conformational change during catalytic activity that involves rearrangement of the dimer to facilitate substrate entry and product formation and egress from the active site.
Since the increasing number of polybutylene adipate terephthalate (PBAT)-based plastics entering the environment, the search for sustainable treatment methods has become a primary focus of contemporary research. Composting offers a novel approach for managing biodegradable plastics. However, a significant challenge in the composting process is how to control nitrogen loss and enhance plastic degradation. In this context, the effect of various additives on nitrogen retention, PBAT plastics degradation, and microbial community dynamics during composting was investigated. The findings revealed that the addition of nitrogen-fixing bacteria Azotobacter vinelandii and biochar (AzBC) significantly improved nitrogen retention and accelerated PBAT rupture within 40 days of composting. Specifically, the PBAT degradation rate in the AzBC group reached 29.6%, which increased by 12.14% (P