This domain is found in the biotin-containing alpha subunit of the Methylcrotonyl-CoA carboxylase complex (MCC) from Pseudomonas aeruginosa and in similar bacterial proteins. MCC is essential for the metabolism of leucine. The alpha subunit is organised into the N-terminal biotin carboxylase (BC), the C-terminal biotin carboxyl carrier protein (BCCP) domains, and a domain that mediates BC-CT interactions (BT domain, this entry). This domain shows a central alpha-helix surrounded by a seven-stranded, highly- twisted anti-parallel beta-sheet, with an overall structure that has great similarity with the beta-barrel of the BT domain of the human MCC [1].

1: An unanticipated architecture of the 750-kDa alpha6beta6 holoenzyme of 3-methylcrotonyl-CoA carboxylase. Huang CS, Ge P, Zhou ZH, Tong L; Nature. 2011;481:219-223. PMID:22158123