Methylmalonic Aciduria Type A Protein (MMAA)

Adenosylcobalamin (AdoCbl) is a cobalamin (cbl; vitamin B12)-containing coenzyme necessary for methylmalonyl-CoA mutase (MUT) activity. The MMAA protein is involved in the translocation of cbl into mitochondria for the final steps of AdoCbl synthesis . The deduced 418-amino acid protein has a calculated molecular mass of 46.5 kD. It contains an N-terminal mitochondrial leader sequence cleavage site, Walker A and B ATP-binding motifs, a Mg(2+)-binding site, and a GTP-binding site. MMAA shares 78.8% sequence identity with mouse Mmaa. Northern blot analysis revealed near ubiquitous expression of transcripts of 1.4, 2.6, and 5.5 kb, with highest expression in liver and skeletal muscle. Liver predominantly expressed the 1.4-kb transcript, while skeletal muscle predominantly expressed the 5.5-kb transcript.