Human biotin-containing subunit of 3-methylcrotonyl-CoA carboxylase gene (MCCA): cDNA sequence, genomic organization, localization to chromosomal band 3q27, and expression

3-Methylcrotonyl-CoA carboxylase (MCCase; EC 6.4.1.4) is a mitochondrial bi otin enzyme and plays an essential role in the catabolism of leucine and is ovalerate in animals, bacterial species, and plants. MCCase consists of two subunits, those that are biotin-containing and non-biotin-containing. The genes responsible for these subunits have been isolated in soybean, Arabido psis thaliana, and tomatoes, but not in mammals. In humans, MCCase deficien cy has been thought to be a rare metabolic disease, but the number of patie nts with MCCase deficiency appears to be increasing with a wide range of cl inical presentations, some that result in a lethal condition and others tha t are asymptomatic. In this report, we have isolated and carried out chromo somal mapping of the gene for the biotin-containing subunit (A subunit) of the human MCCase gene, MCCA. The cDNA predicts an open reading frame coding for a 725-amino-acid protein with mitochondrial signal peptide, biotin car boxylase, and biotin-carrier domains. The gene is composed of at least 19 e xons and covers more than 70 kb of sequence on band q27 of chromosome 3. MC CA was abundantly expressed in mitochondria-rich organs, such as the heart, skeletal muscles, kidney, and liver. In exon 13, we observed a His/Pro pol ymorphism at codon 464 (an A to C transition at nucleotide position 1391 in the cDNA sequence). Then, we determined the DNA sequences of the 5' untran slated region and entire coding regions in two patients with MCCase deficie ncy, but no sequence substitution was detected, suggesting that the gene mu tations might be in the non-biotin-containing subunit (B subunit) gene, MCC B, in these patients. (C) 2001 Academic Press.