This domain is found in Propionyl-coenzyme A carboxylase (PCC), present in Roseobacter denitrificans. PCC is a mitochondrial biotin-dependent enzyme that is essential for the catabolism of certain amino acids, cholesterol, and fatty acids with an odd number of carbon atoms. Since this domain mediates biotin carboxylase-carboxyltransferase interactions it is referred to as the BT domain. The BT domain is located between biotin carboxylase and the biotin carboxyl carrier protein domains. The BT domain shares some structural similarity with the pyruvate carboxylase tetramerization domain of pyruvate carboxylase [1].

1: Crystal structure of the alpha(6)beta(6) holoenzyme of propionyl-coenzyme A carboxylase. Huang CS, Sadre-Bazzaz K, Shen Y, Deng B, Zhou ZH, Tong L; Nature. 2010;466:1001-1005. PMID:20725044