Publications

• Decyanation of vitamin B12 by a trafficking chaperone.

  Kim J., Gherasim C., Banerjee R.

  The mystery of how the cyanide group in vitamin B(12) or cyanocobalamin, discovered 60 years ago, is removed, has been solved by the demonstration that the trafficking chaperone, MMACHC, catalyzes a reductive decyanation reaction. Electrons transferred from NADPH via cytosolic flavoprotein oxidore ... >> More

  The mystery of how the cyanide group in vitamin B(12) or cyanocobalamin, discovered 60 years ago, is removed, has been solved by the demonstration that the trafficking chaperone, MMACHC, catalyzes a reductive decyanation reaction. Electrons transferred from NADPH via cytosolic flavoprotein oxidoreductases are used to cleave the cobalt-carbon bond with reductive elimination of the cyanide ligand. The product, cob(II)alamin, is a known substrate for assimilation into the active cofactor forms, methylcobalamin and 5'-deoxyadenosylcobalamin, and is bound in the "base-off" state that is needed by the two B(12)-dependent target enzymes, methionine synthase and methylmalonyl-CoA mutase. Defects in MMACHC represent the most common cause of inborn errors of B(12) metabolism, and our results explain the observation that fibroblasts from these patients are poorly responsive to vitamin B(12) but show some metabolic correction with aquocobalamin, a cofactor form lacking the cyanide ligand, which is mirrored by patients showing poorer clinical responsiveness to cyano- versus aquocobalamin. << Less

  Proc. Natl. Acad. Sci. U.S.A. 105:14551-14554(2008) [PubMed] [EuropePMC]

• Subcellular location of MMACHC and MMADHC, two human proteins central to intracellular vitamin B(12) metabolism.

  Mah W., Deme J.C., Watkins D., Fung S., Janer A., Shoubridge E.A., Rosenblatt D.S., Coulton J.W.

  MMACHC and MMADHC are the genes responsible for cblC and cblD defects of vitamin B(12) metabolism, respectively. Patients with cblC and cblD defects present with various combinations of methylmalonic aciduria (MMA) and homocystinuria (HC). Those with cblC mutations have both MMA and HC whereas cbl ... >> More

  MMACHC and MMADHC are the genes responsible for cblC and cblD defects of vitamin B(12) metabolism, respectively. Patients with cblC and cblD defects present with various combinations of methylmalonic aciduria (MMA) and homocystinuria (HC). Those with cblC mutations have both MMA and HC whereas cblD patients can present with one of three distinct biochemical phenotypes: isolated MMA, isolated HC, or combined MMA and HC. Based on the subcellular localization of these enzymatic pathways it is thought that MMACHC functions in the cytoplasm while MMADHC functions downstream of MMACHC in both the cytoplasm and the mitochondrion. In this study we determined the subcellular location of MMACHC and MMADHC by immunofluorescence and subcellular fractionation. We show that MMACHC is cytoplasmic while MMADHC is both mitochondrial and cytoplasmic, consistent with the proposal that MMADHC acts as a branch point for vitamin B(12) delivery to the cytoplasm and mitochondria. The factors that determine the distribution of MMADHC between the cytoplasm and mitochondria remain unknown. Functional complementation experiments showed that retroviral expression of the GFP tagged constructs rescued all biochemical defects in cblC and cblD fibroblasts except propionate incorporation in cblD-MMA cells, suggesting that the endogenous mutant protein interferes with the function of the transduced wild type construct. << Less

  Mol. Genet. Metab. 108:112-118(2013) [PubMed] [EuropePMC]

• Occurrence and characterization of cyanocobalamin reductase (NADPH; CN-eliminating) involved in decyanation of cyanocobalamin in Euglena gracilis.

  Watanabe F., Oki Y., Nakano Y., Kitaoka S.

  The activity of an enzyme involved in decyanation of cyanocobalamin was found in the cell homogenate of Euglena gracilis. The enzyme essentially required FAD or FMN, and NADPH as cofactors. The apparent Km for cyanocobalamin and NADPH were 7.1 microM and 0.2 mM, respectively. The enzyme reaction o ... >> More

  The activity of an enzyme involved in decyanation of cyanocobalamin was found in the cell homogenate of Euglena gracilis. The enzyme essentially required FAD or FMN, and NADPH as cofactors. The apparent Km for cyanocobalamin and NADPH were 7.1 microM and 0.2 mM, respectively. The enzyme reaction obeyed allosteric kinetics towards FAD ([FAD]0.5 = 30 microM, n = 2.7; as calculated by the Hill plots). The Euglena enzyme was located in the mitochondria. << Less

  J Nutr Sci Vitaminol (Tokyo) 34:1-10(1988) [PubMed] [EuropePMC]

• Structural basis of multifunctionality in a vitamin B12-processing enzyme.

  Koutmos M., Gherasim C., Smith J.L., Banerjee R.

  An early step in the intracellular processing of vitamin B(12) involves CblC, which exhibits dual reactivity, catalyzing the reductive decyanation of cyanocobalamin (vitamin B(12)), and the dealkylation of alkylcobalamins (e.g. methylcobalamin; MeCbl). Insights into how the CblC scaffold supports ... >> More

  An early step in the intracellular processing of vitamin B(12) involves CblC, which exhibits dual reactivity, catalyzing the reductive decyanation of cyanocobalamin (vitamin B(12)), and the dealkylation of alkylcobalamins (e.g. methylcobalamin; MeCbl). Insights into how the CblC scaffold supports this chemical dichotomy have been unavailable despite it being the most common locus of patient mutations associated with inherited cobalamin disorders that manifest in both severe homocystinuria and methylmalonic aciduria. Herein, we report structures of human CblC, with and without bound MeCbl, which provide novel biochemical insights into its mechanism of action. Our results reveal that CblC is the most divergent member of the NADPH-dependent flavin reductase family and can use FMN or FAD as a prosthetic group to catalyze reductive decyanation. Furthermore, CblC is the first example of an enzyme with glutathione transferase activity that has a sequence and structure unrelated to the GST superfamily. CblC thus represents an example of evolutionary adaptation of a common structural platform to perform diverse chemistries. The CblC structure allows us to rationalize the biochemical basis of a number of pathological mutations associated with severe clinical phenotypes. << Less

  J. Biol. Chem. 286:29780-29787(2011) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.