Methylmalonic Aciduria Type D Protein (MMAD)

Vitamin B12 (cobalamin) is an essential cofactor in several metabolic pathways. Intracellular conversion of cobalamin to adenosylcobalamin in mitochondria and to methylcobalamin in cytoplasm is necessary for homeostasis of methylmalonic acid and homocysteine. C2ORF25 encodes a protein involved in an early step of cobalamin metabolism.

By RT-PCR of fibroblast mRNA, Coelho et al. (2008) obtained a full-length cDNA for C2ORF25. MMAD has a calculated molecular mass of 32.8 kD. It has an N-terminal mitochondrial leader sequence and a putative vitamin B12-binding motif, NxHxxG, at residues 81 through 86. EST database analysis suggested that C2ORF25 is highly expressed in most tissues.