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

Author: Kim, Y-J., Choi, S.Y., Kim, J.E., Jin, K.S., Lee, S.Y., Kim, K-J.

Journal: Biotechnol. J., 12(1):  1-12 (2017. 1)

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_F) by small angle X-ray scattering (SAXS) analysis. The catalytic C-terminal domain of RePhaC1 (RePhaC1_CD) dimer is located at the center of RePhaC1_F, and the N-terminal domain of RePhaC1 (RePhaC1_ND) is located opposite the dimerization subdomain of RePhaC1_CD, indicating that RePhaC1_ND is not directly involved in the enzyme catalysis. The localization studies using RePhaC1_F, RePhaC1_ND and RePhaC1_CD revealed that RePhaC1_ND 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_CD. The serial truncation study on RePhaC1_ND suggested that the predicted five α-helices (N-α3 to N-α7) are required for proper folding and granule binding function of RePhaC1_ND. In addition, the authors also report the SAXS 3D reconstructed model of the RePhaC1_F/RePhaM_ΔC complex (RePhaM_ΔC, PAKKA motif-truncated version of RePhaM). RePhaM forms a complex with RePhaC1 by interacting with RePhaC1_ND and activates RePhaC1 by providing a more extensive surface area for interaction with the growing PHA polymer.