Spectroscopic Studies of the Corrinoid/Iron−Sulfur Protein from Moorella thermoacetica

Abstract

Methyl transfer reactions are important in a number of biochemical pathways. An important class of methyltransferases uses the cobalt cofactor cobalamin, which receives a methyl group from an appropriate methyl donor protein to form an intermediate organometallic methyl-Co bond that subsequently is cleaved by a methyl acceptor. Control of the axial ligation state of cobalamin influences both the mode (i.e., homolytic vs heterolytic) and the rate of Co-C bond cleavage. Here we have studied the axial ligation of a corrinoid iron-sulfur protein (CFeSP) that plays a key role in energy generation and cell carbon synthesis by anaerobic microbes, such as methanogenic archaea and acetogenic bacteria. This protein accepts a methyl group from methyltetrahydrofolate forming Me-Co 3+ CFeSP that then donates a methyl cation (Me) from Me-Co 3+ CFeSP to a nickel site on acetyl-CoA synthase. To unambiguously establish the binding scheme of the corrinoid cofactor in the CFeSP, we have combined resonance Raman, magnetic circular dichroism, and EPR spectroscopic methods with computational chemistry. Our results clearly demonstrate that the MeCo 3+ and Co 2+ states of the CFeSP have an axial water ligand like the free MeCbi + and Co 2+ Cbi + cofactors; however, the Co-OH 2 bond length is lengthened by about 0.2 Å for the protein-bound cofactor. Elongation of the Co-OH 2 bond of the CFeSP-bound cofactor is proposed to make the cobalt center more "Co 1+ -like", a requirement to facilitate heterolytic Co-C bond cleavage.

Structural insights into methyltransfer reactions of a corrinoid iron–sulfur protein involved in acetyl-CoA synthesis

“…2 A and C). The presence of an axial water ligand bound to cobalt in both the ϩ2 and ϩ3 oxidation state is in agreement with recent spectroscopic data of CoFeSP Mt (16).…”

“…For CoFeSP Mt , it was recently shown that a water ligand can also be found in the methylated state of the corrinoid cofactor (16), indicating structural changes that may allow a water molecule to bind to the cobalt-␣ position. It is evident from the crystal structure that any methyl group transfer to or from the cobamide cofactor depends on a conformation different from the one observed, because the cobalt-␣ and -␤ positions are shielded by the protein matrix.…”

Draft genome of an Aerophobetes bacterium reveals a facultative lifestyle in deep-sea anaerobic sediments

“…The methyl transfer reaction is critical for the synthesis of acetyl-CoA. The C/Fe-SP involved in the Wood-Ljungdahl pathway uses the cobalt cofactor cobalamin to receive a methyl group [30]. Prior to being transferred to a methyl acceptor, an intermediate organometallic methyl-cobalt bond is formed.…”

Insight into the mechanism of biological methanol activation based on the crystal structure of the methanol-cobalamin methyltransferase complex

“…3 attributes a key function in Co(I) methylation to His-136 and the other components of the catalytic triad, which has been found in all corrinoid proteins catalyzing methyl transfer reactions except in the corrinoid ironsulfur protein (42). The importance of the axial ligand His-136 for the (MtaBC) 2 complex for the catalytic reaction is underscored by the finding that the methylation rate of free cob(I)inamide (which lacks the imidazole base) with methanol catalyzed by MtaB is completely dependent on the presence of imidazole, whereas the coenzyme M-dependent demethylation catalyzed by MtaA is inhibited in the presence of imidazole (9,43).…”