CbiK

CbiK
PFAM accession number:PF06180
Interpro abstract (IPR010388):

This group, typified by Salmonella typhimurium CbiK, contains anaerobic cobalt chelatases that act in the anaerobic cobalamin biosynthesis pathway [ (PUBMED:9150215) (PUBMED:11215515) ].

Cobalamin (vitamin B12) can be complexed with metal via ATP-dependent reactions (aerobic pathway) (e.g., in Pseudomonas denitrificans) or via ATP-independent reactions (anaerobic pathway) (e.g., in S. typhimurium) [ (PUBMED:8905078) (PUBMED:11469861) ]. The corresponding cobalt chelatases are not homologous. This group belongs to the class of ATP-independent, single-subunit chelatases that also includes distantly related protoporphyrin IX (PPIX) ferrochelatase (HemH) (Class II chelatases) [ (PUBMED:12686546) ]. The structure of S. typhimurium CbiK shows that it has a remarkably similar topology to Bacillus subtilis ferrochelatase despite only weak sequence conservation [ (PUBMED:10451360) ]. Both enzymes contain a histidine residue identified as the metal ion ligand, but CbiK contains a second histidine in place of the glutamic acid residue identified as a general base in PPIX ferrochelatase [ (PUBMED:10451360) ]. Site-directed mutagenesis has confirmed a role for this histidine and a nearby glutamic acid in cobalt binding, modulating metal ion specificity as well as catalytic efficiency [ (PUBMED:10451360) ].

It should be noted that CysG and Met8p, which are multifunctional proteins associated with siroheme biosynthesis, include chelatase activity and can therefore be considered as the third class of chelatases [ (PUBMED:12686546) ]. As with the class II chelatases, they do not require ATP for activity. However, they are not structurally similar to HemH or CbiK, and it is likely that they have arisen by the acquisition of a chelatase function within a dehydrogenase catalytic framework [ (PUBMED:11980703) (PUBMED:12686546) ].

GO process:anaerobic cobalamin biosynthetic process (GO:0019251)
GO function:sirohydrochlorin cobaltochelatase activity (GO:0016852)

This is a PFAM domain. For full annotation and more information, please see the PFAM entry CbiK