Structure and function of the N‐terminal domain of Ralstonia eutropha polyhydroxyalkanoate synthase, and the proposed structure and mechanisms of the whole enzyme

Abstract

Polyhydroxyalkanoates (PHAs) are natural polyesters synthesized by numerous microorganisms as energy and reducing power storage materials, and have attracted much attention as substitutes for petroleum-based plastics. In an accompanying paper, the authors reported the crystal structure of the C-terminal domain of Ralstonia eutropha PHA synthase (PhaC1). Here, the authors report the 3D reconstructed model of full-length of R. eutropha PhaC1 (RePhaC1 ) by small angle X-ray scattering (SAXS) analysis. The catalytic C-terminal domain of RePhaC1 (RePhaC1 ) dimer is located at the center of RePhaC1 , and the N-terminal domain of RePhaC1 (RePhaC1 ) is located opposite the dimerization subdomain of RePhaC1 , indicating that RePhaC1 is not directly involved in the enzyme catalysis. The localization studies using RePhaC1 , RePhaC1 and RePhaC1 revealed that RePhaC1 plays important roles in PHA polymerization by localizing the enzyme to the PHA granules and stabilizing the growing PHA polymer near the active site of RePhaC1 . The serial truncation study on RePhaC1 suggested that the predicted five α-helices (N-α3 to N-α7) are required for proper folding and granule binding function of RePhaC1 . In addition, the authors also report the SAXS 3D reconstructed model of the RePhaC1 /RePhaM complex (RePhaM , PAKKA motif-truncated version of RePhaM). RePhaM forms a complex with RePhaC1 by interacting with RePhaC1 and activates RePhaC1 by providing a more extensive surface area for interaction with the growing PHA polymer.

New Insights into PhaM-PhaC-Mediated Localization of Polyhydroxybutyrate Granules in Ralstonia eutropha H16

“…Transmission electron microscopic investigation confirmed that PHB granules in R. eutropha colocalized with the bacterial nucleoid (29). Attachment of PhaM to the PHB synthase PhaC was recently confirmed in three other laboratories (17,30,31). Binding of PHB granules to the nucleoid as a scaffold enables the cells to equally distribute PHB/PHA granules to daughter cells during cell division.…”

“…PhaC of Ralstonia eutropha has been solved (16)(17)(18). The finding of so many proteins with different functions on the PHB granule surface has led to the classification of PHB granules as multifunctional units, and the designation carbonosomes has been proposed for these organelle-like structures (19).…”

Unveiling the 30‐year mystery of polyhydroxyalkanoate (PHA) synthase

“…It has been my great pleasure to read the two papers entitled "Crystal structure of Ralstonia eutropha polyhydroxyalkanoate synthase C-terminal domain and reaction mechanisms" by Kim et al [1], and "Structure and function of the N-terminal domain of Ralstonia eutropha polyhydroxyalkanoate synthase, and the proposed structure and mechanisms of the whole enzyme" by Kim et al [2].…”

“…Kim et al [2] then for the first time report the 3D reconstructed model of full length PHA synthase from R. eutropha, and performed several biochemical studies. These two studies provide feasibility for rational engineering of PHA synthase toward more efficient production of bioplastics, more broad PHA structure diversity and possibly controllable PHA molecular weights.…”

Editorial: Methods and advances for systems and synthetic biology, nanobiotech and medicine

“…This special issue firstly brings you two back-to-back papers from Professor Kyung-Jin Kim and Professor Sang Yup Lee [1,2] who have unveiled the 30-year mystery of polyhydroxyalkanoate (PHA) synthase. The studies report the crystal structure of PHA synthase from Ralstonia eutropha, the best studied bacterium for PHA production, as well as the structural basis for the detailed molecular mechanisms of PHA biosynthesis.…”