Cobalamin (vitamin B12) biosynthesis CobJ/CibH, precorrin-3B C17-methyltransferase, core

Cobalamin (vitamin B12) biosynthesis CobJ/CibH, precorrin-3B C17-methyltransferase, core(InterPro Protein Domain record)

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Cobalamin (vitamin B12) biosynthesis CobJ/CibH, precorrin-3B C17-methyltransferase, core

InterPro Protein Domain record

description http://metadb.riken.jp/db/SciNetS_rib124i/prib124u1i

Cobalamin (vitamin B12) is a structurally complex cofactor, consisting of a modified tetrapyrrole with a centrally chelated cobalt. Cobalamin is usually found in one of two biologically active forms: methylcobalamin and adocobalamin. Most prokaryotes, as well as animals, have cobalamin-dependent enzymes, whereas plants and fungi do not appear to use it. In bacteria and archaea, these include methionine synthase, ribonucleotide reductase, glutamate and methylmalonyl-CoA mutases, ethanolamine ammonia lyase, and diol dehydratase [<cite idref="PUB00015657"/>]. In mammals, cobalamin is obtained through the diet, and is required for methionine synthase and methylmalonyl-CoA mutase [<cite idref="PUB00035308"/>]. There are at least two distinct cobalamin biosynthetic pathways in bacteria [<cite idref="PUB00014672"/>]:<ul><li>Aerobic pathway that requires oxygen and in which cobalt is inserted late in the pathway [<cite idref="PUB00035309"/>]; found in <taxon tax_id="43306">Pseudomonas denitrificans</taxon> and <taxon tax_id="1061">Rhodobacter capsulatus</taxon>.</li><li>Anaerobic pathway in which cobalt insertion is the first committed step towards cobalamin synthesis [<cite idref="PUB00035310"/>]; found in <taxon tax_id="602">Salmonella typhimurium</taxon>, <taxon tax_id="1404">Bacillus megaterium</taxon>, and <taxon tax_id="1752">Propionibacterium freudenreichii subsp. shermanii</taxon>. </li></ul>Either pathway can be divided into two parts: (1) corrin ring synthesis (differs in aerobic and anaerobic pathways) and (2) adenosylation of corrin ring, attachment of aminopropanol arm, and assembly of the nucleotide loop (common to both pathways) [<cite idref="PUB00009744"/>]. There are about 30 enzymes involved in either pathway, where those involved in the aerobic pathway are prefixed Cob and those of the anaerobic pathway Cbi. Several of these enzymes are pathway-specific: CbiD, CbiG, and CbiK are specific to the anaerobic route of S. typhimurium, whereas CobE, CobF, CobG, CobN, CobS, CobT, and CobW are unique to the aerobic pathway of P. denitrificans.This entry represents CobJ and CbiH precorrin-3B C(17)-methyltransferase (<db_xref db="EC" dbkey="2.1.1.131"/>), both as stand-alone enzymes and when CobJ forms part of a bifunctional enzyme. In the aerobic pathway, once CobG has generated precorrin-3b, CobJ catalyses the methylation of precorrin-3b at C-17 to form precorrin-4 (the extruded methylated C-20 fragment is left attached as an acyl group at C-1) [<cite idref="PUB00009744"/>]. In the corresponding anaerobic pathway, CbiH carries out this ring contraction, using cobalt-precorrin-3b as a substrate to generate a tetramethylated delta-lactone.These proteins belong to the superfamily of tetrapyrrole (corrin/porphyrin) methylases (<db_xref db="INTERPRO" dbkey="IPR000878"/>), which includes methylases that use S-adenosylmethionine (S-AdoMet) in the methylation of diverse substrates. A number of other methylases in the cobalamin biosynthesis pathway also belong to this domain superfamily (precorrin-3 methylase, <db_xref db="INTERPRO" dbkey="IPR012203"/>, <db_xref db="INTERPRO" dbkey="IPR012059"/>, <db_xref db="INTERPRO" dbkey="IPR012382"/>, <db_xref db="INTERPRO" dbkey="IPR012797"/>, amongst others), and a fusion of precorrin-3B C17-methyltransferases with precorrin isomerase is represented by <db_xref db="INTERPRO" dbkey="IPR014422"/>.Nomenclature note: precorrin-3B C17-methyltransferase is one of the two methyltransferases often referred to as precorrin-3 methylase (the other is precorrin-4 C11-methyltransferase, <db_xref db="EC" dbkey="2.1.1.133"/>).

label http://www.w3.org/2000/01/rdf-schema#label