Cobalt chelatase

{{Short description|Enzyme}}

{{infobox enzyme

| Name = cobalt chelatase

| EC_number = 6.6.1.2

| CAS_number = 81295-49-0

| GO_code = 0051116

| image = EVWong CC2XVX raytraced.png

| caption = Putative cobalt chelatase monomer from Desulvobrio vulgaris.{{cite journal |last1=Romão |first1=Célia V. |last2=Ladakis |first2=Dimitrios |last3=Lobo |first3=Susana A. L. |last4=Carrondo |first4=Maria A. |last5=Brindley |first5=Amanda A. |last6=Deery |first6=Evelyne |last7=Matias |first7=Pedro M. |last8=Pickersgill |first8=Richard W. |last9=Saraiva |first9=Lígia M. |last10=Warren |first10=Martin J. |title=Evolution in a family of chelatases facilitated by the introduction of active site asymmetry and protein oligomerization |journal=Proceedings of the National Academy of Sciences |date=4 January 2011 |volume=108 |issue=1 |pages=97–102 |doi=10.1073/pnas.1014298108 |pmid=21173279 |pmc=3017170 |doi-access=free }}

}}

{{Pfam box |Symbol = CobT |Name = Cobalt chelatase, CobT subunit |Pfam = PF06213 |InterPro = IPR006538 |PROSITE = |PDB = }}

Cobalt chelatase ({{EnzExplorer|6.6.1.2}}) is an enzyme that catalyzes the chemical reaction

:ATP + hydrogenobyrinic acid a,c-diamide + Co²⁺ + H₂O $\backslash rightleftharpoons$ ADP + phosphate + cob(II)yrinic acid a,c-diamide + H⁺

The four substrates of this enzyme are ATP, hydrogenobyrinic acid a,c-diamide, Co²⁺, and H₂O; its four products are ADP, phosphate, cob(II)yrinic acid a,c-diamide, and H⁺.

The aerobic cobalt chelatase (aerobic cobalamin biosynthesis pathway){{cite journal |vauthors=Crouzet J, Cameron B, Cauchois L, Rigault S, Blanche F, Guilhot C, Levy-schil S, Rouyez MC |title=Genetic and sequence analyses of a Pseudomonas denitrificans DNA fragment containing two cob genes |journal=J. Bacteriol. |volume=173 |issue=19 |pages=6058–6065 |year=1991 |pmid=1917840 |pmc=208352|doi=10.1128/jb.173.19.6058-6065.1991 }}{{cite journal |vauthors=Crouzet J, Cameron B, Blanche F, Thibaut D, Debussche L, Couder M |title=Assay, purification, and characterization of cobaltochelatase, a unique complex enzyme catalyzing cobalt insertion in hydrogenobyrinic acid a,c-diamide during coenzyme B12 biosynthesis in Pseudomonas denitrificans |journal=J. Bacteriol. |volume=174 |issue=22 |pages=7445–7451 |year=1992 |pmid=1429466 |pmc=207441|doi=10.1128/jb.174.22.7445-7451.1992 }} consists of three subunits, CobT, CobN ({{InterPro|IPR003672}}) and CobS ({{InterPro|IPR006537}}).

The macrocycle of vitamin B12 can be complexed with metal via the ATP-dependent reactions in the aerobic pathway (e.g., in Pseudomonas denitrificans) or via ATP-independent reactions of sirohydrochlorin in the anaerobic pathway (e.g., in Salmonella typhimurium).{{cite journal |vauthors=Roth JR, Lawrence JG, Bobik TA |title=Cobalamin (coenzyme B12): synthesis and biological significance |journal=Annu. Rev. Microbiol. |volume=50 |pages=137–181 |year=1996 |pmid=8905078 |doi=10.1146/annurev.micro.50.1.137|s2cid=36290299 |url=http://pdfs.semanticscholar.org/d859/d9a7b8f4dcebb41a5992232b36cf2f4351d5.pdf |archive-url=https://web.archive.org/web/20190307012130/http://pdfs.semanticscholar.org/d859/d9a7b8f4dcebb41a5992232b36cf2f4351d5.pdf |url-status=dead |archive-date=2019-03-07 }}{{cite journal |vauthors=Willows RD, Al-Karadaghi S, Hansson M, Fodje MN, Hansson A, Olsen JG, Gough S |title=Interplay between an AAA module and an integrin I domain may regulate the function of magnesium chelatase |journal=J. Mol. Biol. |volume=311 |issue=1 |pages=111–122 |year=2001 |pmid=11469861 |doi=10.1006/jmbi.2001.4834}} The corresponding cobalt chelatases are not homologous. However, aerobic cobalt chelatase subunits CobN and CobS are homologous to Mg-chelatase subunits BchH and BchI, respectively. CobT, too, has been found to be remotely related to the third subunit of Mg-chelatase, BchD (involved in bacteriochlorophyll synthesis, e.g., in Rhodobacter capsulatus).

This enzyme belongs to the family of ligases, specifically those forming nitrogen-D-metal bonds in coordination complexes. The systematic name of this enzyme class is hydrogenobyrinic-acid-a,c-diamide:cobalt cobalt-ligase (ADP-forming). Other names in common use include hydrogenobyrinic acid a,c-diamide cobaltochelatase, CobNST, and CobNCobST. This enzyme is part of the biosynthetic pathway to cobalamin (vitamin B₁₂) in aerobic bacteria.