Related Experiment Video
Updated: Dec 15, 2025

Sequence-specific Labeling of Nucleic Acids and Proteins with Methyltransferases and Cofactor Analogues
Published on: November 22, 2014
Naturally occurring cobalamin (B12) analogs can function as cofactors for human methylmalonyl-CoA mutase
Olga M Sokolovskaya1, Tanja Plessl2, Henry Bailey3
1Department of Plant & Microbial Biology, University of California, Berkeley, CA, USA; Department of Chemistry, University of California, Berkeley, CA, USA.
Abstract:
Cobalamin, commonly known as vitamin B12, is an essential micronutrient for humans because of its role as an enzyme cofactor. Cobalamin is one of over a dozen structurally related compounds - cobamides - that are found in certain foods and are produced by microorganisms in the human gut. Very little is known about how different cobamides affect B12-dependent metabolism in human cells. Here, we test in vitro how diverse cobamide cofactors affect the function of methylmalonyl-CoA mutase (MMUT), one of two cobalamin-dependent enzymes in humans. We find that, although cobalamin is the most effective cofactor for MMUT, multiple cobamides support MMUT function with differences in binding affinity (Kd), binding kinetics (kon), and concentration dependence during catalysis (KM, app). Additionally, we find that six disease-associated MMUT variants that cause cobalamin-responsive impairments in enzymatic activity also respond to other cobamides, with the extent of catalytic rescue dependent on the identity of the cobamide. Our studies challenge the exclusive focus on cobalamin in the context of human physiology, indicate that diverse cobamides can support the function of a human enzyme, and suggest future directions that will improve our understanding of the roles of different cobamides in human biology.
Related Concept Videos
Cofactors and Coenzymes
Cofactors can be metallic ions or organic molecules called coenzymes. These types of helper...
Cofactors and Coenzymes
Phase II Reactions: Methylation Reactions
The mechanism of methylation unfolds in two stages. The first stage sees a methyltransferase enzyme facilitating the transfer of a methyl group from S-adenosylmethionine (SAM) to the substrate, forming S-adenosylhomocysteine (SAH). The second stage involves further metabolism of SAH into homocysteine, which can be recycled...
Loss of Carboxy Group as CO2: Decarboxylation of Malonic Acid Derivatives
Inborn Errors of Metabolism
Role of Reduced Coenzymes NADH and FADH₂

