Human biotin-containing subunit of 3-methylcrotonyl-CoA carboxylase gene (MCC-2): cDNA sequence, genomic organization, and localization to chromosome 3q27. T. Fukuda¹, K. Obata¹, R.. Morishita¹, K. Shigemoto¹, S. Abe², M. Yoshino³, S. Yamaguchi⁴, S. Asakawa⁵, N. Shimizu⁵, I. Kondo¹. 1) Dept. of Hygiene, Ehime Uni. School of Med., Ehime, Japan; 2) Dept. of Biological Resources, Faculty of Agriculture, Ehime Univ., Ehime, Japan; 3) Dept. of Pediatr. and Child Health, Kurume Univ. School of Med., Fukuoka, Japan; 4) Dept. of Pediatr., Shimane Med. Univ. ,Izumo, Japan; 5) Dept. of Mol. Biology, Keio Univ. School of Med.,Tokyo,Japan.
   3-methylcrotonyl-CoA carboxylase (MCCase, EC 6.4.1.4) is a mitochondrial biotin enzyme, and plays an essential role in the catabolism of leucine and isovalerate in animals, bacterial species and plants. MCCase consists of two subunits: biotin-containing and non-biotin- containing subunits. The gene responsible for these subunits has been isolated in Arabidopsis thaliana but bit in mammals. In human, MCCase deficiency appeared increasing with a wide range of clinical presentations; some that result in lethal conditions, and others that are non-symptomatic. We have isolated and carried out chromosomal mapping of the gene for the biotin-containing subunit (beta-subunit) of the human MCCase, MCC-2. MCC-2 cDNA contained an open reading frame encoding for a 725 amino acid protein with mitochondrial signal peptide, biotin carboxylase and biotin-carrier domains. The gene is composed of at least 19 exons and covers more than 70kb of sequence on q27 of chromosome 3. MCC-2 was abundantly expressed in mitochondrial-rich organs, such as the heart, skeletal muscles, kidney and liver. In exon 13, a His/Pro polymorphism in codon 464 (an A to C transversion at nucleotide position 1391 in the cDNA sequence) was detected. Then, we determined the DNA sequences of the entire coding regions in two patients with MCCase deficiency, but no sequence changes were detected, suggesting that the gene mutations might be in the non-biotin-containing subunit, MCC-alpha, in these patients.