Crystal structure of the large subunit of cobaltochelatase from Mycobacterium tuberculosis.

Cobaltochelatase in aerobic cobalamin biosynthesis is a complex composed of three subunits. The large subunit CobN is a 140-kDa protein and is homologous to the ChlH subunit of magnesium chelatase. Previously we have reported the 2.5-Å structure of a cyanobacterial ChlH. Here we present the 1.8-Å structure of CobN from Mycobacterium tuberculosis. The overall structure of CobN and ChlH is similar, but significant difference occurs in the head domain. Structural comparison of domains between the two proteins unravels candidate regions for substrate binding and helps to locate a triad of residues that may be essential for metal ion binding.