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CSA entry for 1f2v
Original Entry
Title:
Isomerase
Compound:
Precorrin-8x methylmutase
Mutant:
No
UniProt/Swiss-Prot:
P21638-COBH_PSEDE
EC Class:
5.4.1.2
Other CSA Entries:
Overview of all sites for 1f2v
Homologues of 1f2v
Entries for UniProt/Swiss-Prot: P21638
Entries for EC: 5.4.1.2
Other Databases:
PDB entry: 1f2v
PDBsum entry: 1f2v
UniProt/Swiss-Prot: P21638
IntEnz entry: 5.4.1.2
Literature Report:
Introduction:
Precorrin-8x methyl mutase (CobH) catalyses the migration of a methyl group attached to C-11 of the substrate, precorrin-8x, to the adjacent C-12 to give the product hydrogenobyrinic acid (HBA).This is a step in the aerobic biosynthesis of the corrin macrocycle of vitamin B12.
Mechanism:
CobH is one of a few known enzymes that catalyse pericyclic reactions.

His 43 protonates the nitrogen of the pyrrolenine C ring of precorrin-8x, which triggers a suprafacial [1,5]-sigmatropic rearrangement; the methyl group passes from C-11 to C-12 in a single concerted step, with the double bonds in the ring shifting position.

Return of the proton to His 43 is inferred.

Ser 17 is hydrogen bonded to His 43 and probably has a role in tuning the pKa of His 43, but this role is not yet explored in the literature.
Sites:

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Found by:
Literature reference 

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
HISA 43 43Sidechain
Acid/baseSubstrate
His 43 acts as a proton donor to the nitrogen of the C ring of the substrate. It probably also deprotonates the product at the same position.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11470433 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 11470433 Current protein Conservation of residue
Notes:
A stepwise mechanism may also be possible, although evidence favours the pericyclic mechanism.
References:
1
Crystal structure of precorrin-8x methyl mutase.
L. W. Shipman and D. Li and C. A. Roessner and A. I. Scott and J. C. Sacchettini
Structure 9, (7) 587-96, (2001).
11470433
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