Intermediates along the NAD⁺cyclisation reaction pathway of ADP-ribosyl cyclase

Abstract

Poster SessionsC786 peak wavelength of gold, and processed with HKL2000. Phasing, model building and refinement were conducted using PHENIX, REFMAC5, COOT and other programs of CCP4. Electron densities for the catalytic domain of the enzyme were clearly obtained, but those for the linker and PHB-binding domains were not, in spite that there is remaining space for these domains to be packed in the crystal lattice.The overall structure of the catalytic domain represented an α/β hydrolase fold which is often observed for the large superfamily of esterases including lipases and carboxypeptidases. A cervice was formed on the surface of the protein, at the bottom of which are located catalytic triad residues Ser-166, Asp-241 and His-300. The structure was compared with that of a fungal single-domain depolymerase with circular permuted polypeptide connectivity [1]. These two enzymes differ in the product composition. The main product is dimer of R-3-hydroxybutyrate for the bacterial enzyme, whereas it is monomer for the fungal enzyme. Structures of loop regions around the active site were different between the two enzymes. This may differentiate the mode of interactions with monomer units of the substrate polymer for these enzymes, which may explain the difference in the product composition.[1] T.