1hbn

From Proteopedia

Revision as of 14:04, 18 December 2007

METHYL-COENZYME M REDUCTASE

Overview

Methyl-coenzyme M reductase (MCR) catalyzes the final reaction of the, energy conserving pathway of methanogenic archaea in which methylcoenzyme, M and coenzyme B are converted to methane and the heterodisulfide, CoM-S-S-CoB. It operates under strictly anaerobic conditions and contains, the nickel porphinoid F430 which is present in the nickel (I) oxidation, state in the active enzyme. The known crystal structures of the inactive, nickel (II) enzyme in complex with coenzyme M and coenzyme B, (MCR-ox1-silent) and in complex with the heterodisulfide CoM-S-S-CoB, (MCR-silent) were now refined at 1.16 A and 1.8 A resolution, respectively. The atomic resolution structure of MCR-ox1-silent describes, the exact geometry of the cofactor F430, of the active site residues and, of the modified amino acid residues. Moreover, the observation of 18 Mg2+, and 9 Na+ ions at the protein surface of the 300 kDa enzyme specifies, typical constituents of binding sites for either ion. The MCR-silent and, MCR-ox1-silent structures differed in the occupancy of bound water, molecules near the active site indicating that a water chain is involved, in the replenishment of the active site with water molecules. The, structure of the novel enzyme state MCR-red1-silent at 1.8 A resolution, revealed an active site only partially occupied by coenzyme M and coenzyme, B. Increased flexibility and distinct alternate conformations were, observed near the active site and the substrate channel. The electron, density of the MCR-red1-silent state aerobically co-crystallized with, coenzyme M displayed a fully occupied coenzyme M-binding site with no, alternate conformations. Therefore, the structure was very similar to the, MCR-ox1-silent state. As a consequence, the binding of coenzyme M induced, specific conformational changes that postulate a molecular mechanism by, which the enzyme ensures that methylcoenzyme M enters the substrate, channel prior to coenzyme B as required by the active-site geometry. The, three different enzymatically inactive enzyme states are discussed with, respect to their enzymatically active precursors and with respect to the, catalytic mechanism.

About this Structure

1HBN is a Protein complex structure of sequences from Methanothermobacter thermautotrophicus with ZN, MG, NA, CL, F43, TP7, COM and GOL as ligands. Known structural/functional Sites: , , , , and . Full crystallographic information is available from OCA.

Reference

On the mechanism of biological methane formation: structural evidence for conformational changes in methyl-coenzyme M reductase upon substrate binding., Grabarse W, Mahlert F, Duin EC, Goubeaud M, Shima S, Thauer RK, Lamzin V, Ermler U, J Mol Biol. 2001 May 25;309(1):315-30. PMID:11491299

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