Hannibal Luciana, Kim Jihoe, Brasch Nicola E, Wang Sihe, Rosenblatt David S, Banerjee Ruma, Jacobsen Donald W
Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
Mol Genet Metab. 2009 Aug;97(4):260-6. doi: 10.1016/j.ymgme.2009.04.005. Epub 2009 Apr 16.
The MMACHC gene product of the cblC complementation group, referred to as the cblC protein, catalyzes the in vitro and in vivo decyanation of cyanocobalamin (vitamin B(12)). We hypothesized that the cblC protein would also catalyze the dealkylation of newly internalized methylcobalamin (MeCbl) and 5'-deoxyadenosylcobalamin (AdoCbl), the naturally occurring alkylcobalamins that are present in the diet. The hypothesis was tested in cultured endothelial cells using [(57)Co]-AdoCbl and MeCbl analogs consisting of [(57)Co]-labeled straight-chain alkylcobalamins ranging from C2 (ethylcobalamin) to C6 (hexylcobalamin). [(57)Co]-AdoCbl was converted to [(57)Co]-MeCbl by cultured bovine aortic endothelial cells, suggesting that a dealkylation process likely involving the cblC protein removed the 5'-deoxyadenosyl alkyl group. Surprisingly, all of the straight-chain alkylcobalamins served as substrates for the biosynthesis of both AdoCbl and MeCbl. Dealkylation was then assessed in normal skin fibroblasts and fibroblasts derived from three patients with mutations in the MMACHC gene. While normal skin fibroblasts readily converted [(57)Co]-propylcobalamin to [(57)Co]-AdoCbl and [(57)Co]-MeCbl, there was little or no conversion in cblC mutant fibroblasts. These studies suggest that the CblC protein is responsible for early processing of both CNCbl (decyanation) and alkylcobalamins (dealkylation) in mammalian cells.
cblC互补组的MMACHC基因产物，即cblC蛋白，在体外和体内催化氰钴胺素（维生素B12）的脱氰反应。我们推测，cblC蛋白也会催化新内化的甲基钴胺素（MeCbl）和5'-脱氧腺苷钴胺素（AdoCbl）的脱烷基反应，这两种物质是饮食中天然存在的烷基钴胺素。我们使用[57Co]-AdoCbl和由[57Co]标记的直链烷基钴胺素（从C2（乙基钴胺素）到C6（己基钴胺素））组成的MeCbl类似物，在培养的内皮细胞中对这一推测进行了验证。培养的牛主动脉内皮细胞将[57Co]-AdoCbl转化为[57Co]-MeCbl，这表明一个可能涉及cblC蛋白的脱烷基过程去除了5'-脱氧腺苷烷基。令人惊讶的是，所有直链烷基钴胺素都作为AdoCbl和MeCbl生物合成的底物。然后，我们在正常皮肤成纤维细胞和来自三名MMACHC基因突变患者的成纤维细胞中评估了脱烷基反应。虽然正常皮肤成纤维细胞能轻易地将[57Co]-丙基钴胺素转化为[57Co]-AdoCbl和[57Co]-MeCbl，但在cblC突变的成纤维细胞中几乎没有或完全没有转化。这些研究表明，CblC蛋白负责哺乳动物细胞中CNCbl（脱氰）和烷基钴胺素（脱烷基）的早期加工过程。
