Cobalt complex structure of the sirohydrochlorin chelatase SirB from Bacillus subtilis subsp. Spizizenii

초록

Chelatase catalyzes the insertion of divalent metal into tetrapyrroleand plays a key role in the biosynthesis of metallatedtetrapyrroles, such as cobalamin, siroheme, heme, and chlorophyll. SirB is a sirohydrochlorin (SHC) chelatase that generatescobalt-SHC or iron-SHC by inserting cobalt or iron into thecenter of sirohydrochlorin tetrapyrrole. To provide structuralinsights into the metal-binding and SHC-recognition mechanismsof SirB, we determined the crystal structure of SirB fromBacillus subtilis subsp. spizizenii (bssSirB) in complex withcobalt ions. bssSirB forms a monomeric α/β structure thatconsists of two domains, an N-terminal domain (NTD) and aC-terminal domain (CTD). The NTD and CTD of bssSirB adoptsimilar structures with a four-stranded β-sheet that is decoratedby α-helices. bssSirB presents a highly conserved cavity that isgenerated between the NTD and CTD and interacts with a cobaltion on top of the cavity using two histidine residues of the NTD. Moreover, our comparative structural analysis suggests thatbssSirB would accommodate an SHC molecule into the interdomaincavity. Based on these structural findings, we proposethat the cavity of bssSirB functions as the active site wherecobalt insertion into SHC occurs.

키워드