This family of proteins forms part of the cobalt-transport complex in prokaryotes, CbiMNQO. CbiMNQO and NikMNQO are the most widespread groups of microbial transporters for cobalt and nickel ions and are unusual uptake systems as they consist of eg two transmembrane components (CbiM and CbiQ), a small membrane-bound component (CbiN) and an ATP-binding protein (CbiO) but no extracytoplasmic solute-binding protein. Similar components constitute the nickel transporters with some variability in the small membrane-bound component, either NikN or NikL, which are not similar to CbiN at the sequence level. CbiM is the substrate-specific component of the complex and is a seven-transmembrane protein [2]. The CbiMNQO and NikMNQO systems form part of the coenzyme B12 biosynthesis pathway [3]. The NikM protein is Pfam:PF10670.

1: Characterization of the cobalamin (vitamin B12) biosynthetic genes of Salmonella typhimurium. Roth JR, Lawrence JG, Rubenfield M, Kieffer-Higgins S, Church GM; J Bacteriol 1993;175:3303-3316. PMID:8501034

2: Comparative and functional genomic analysis of prokaryotic nickel and cobalt uptake transporters: evidence for a novel group of ATP-binding cassette transporters. Rodionov DA, Hebbeln P, Gelfand MS, Eitinger T; J Bacteriol. 2006;188:317-327. PMID:16352848

3: The complete coenzyme B12 biosynthesis gene cluster of Lactobacillus reuteri CRL1098. Santos F, Vera JL, van der Heijden R, Valdez G, de Vos WM, Sesma F, Hugenholtz J; Microbiology. 2008;154:81-93. PMID:18174128