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1req

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Image:1req.gif

1req, resolution 2.0Å

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METHYLMALONYL-COA MUTASE

Overview

BACKGROUND. The enzyme methylmalonyl-coenzyme A (CoA) mutase, an alphabeta, heterodimer of 150 kDa, is a member of a class of enzymes that uses, coenzyme B12 (adenosylcobalamin) as a cofactor. The enzyme induces the, formation of an adenosyl radical from the cofactor. This radical then, initiates a free-radical rearrangement of its substrate, succinyl-CoA, to, methylmalonyl-CoA. RESULTS. Reported here is the crystal structure at 2 A, resolution of methylmalonyl-CoA mutase from Propionibacterium shermanii in, complex with coenzyme B12 and with the partial substrate desulpho-CoA, (lacking the succinyl group and the sulphur atom of the substrate). The, coenzyme is bound by a domain which shares a similar fold to those of, flavodoxin and the B12-binding domain of methylcobalamin-dependent, methionine synthase. The cobalt atom is coordinated, via a long bond, to a, histidine from the protein. The partial substrate is bound along the axis, of a (beta/alpha)8 TIM barrel domain. CONCLUSIONS. The histidine-cobalt, distance is very long (2.5 A compared with 1.95-2.2 A in free cobalamins), suggesting that the enzyme positions the histidine in order to weaken the, metal-carbon bond of the cofactor and favour the formation of the initial, radical species. The active site is deeply buried, and the only access to, it is through a narrow tunnel along the axis of the TIM barrel domain.

About this Structure

1REQ is a Protein complex structure of sequences from Propionibacterium freudenreichii subsp. shermanii with B12, DCA and GOL as ligands. Active as Methylmalonyl-CoA mutase, with EC number 5.4.99.2 Full crystallographic information is available from OCA.

Reference

How coenzyme B12 radicals are generated: the crystal structure of methylmalonyl-coenzyme A mutase at 2 A resolution., Mancia F, Keep NH, Nakagawa A, Leadlay PF, McSweeney S, Rasmussen B, Bosecke P, Diat O, Evans PR, Structure. 1996 Mar 15;4(3):339-50. PMID:8805541

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