Abstract
An S-adenosylmethionine (SAM)-dependent methyltrasferase, BchU, catalyzes methylation at C-20 position of chlorin moiety in bacteriochlorophyll c biosynthetic pathway, however, the methylation mechanism underlying the bacteriochlorophyll c biosynthesis is poorly understood. We have determined the crystal structure of BchU in order to elucidate its reaction mechanism at the molecular level.
Recombinant BchU from Chlorobium tepidum was overexpressed in E. coli, purified, and crystallized. We collected diffraction data using synchrotron radiation at SPring-8 and determined the crystal structure at 2.3 A resolution. The structure of BchU consists of two domains; N-terminal domain and C-terminal domain. The N-terminal domain is involved in dimerizaion and the C-terminal domain contains a typical Class I motif. In addition, we determined the BchU structure in complex with SAM. These structural features and analysis of putative substrate-binding pocket provide invaluable information for the methylation mechanism of BchU.
