Urea carboxylase (UC) catalyses a two-step, ATP- and biotin-dependent carboxylation reaction of urea. It is composed of biotin carboxylase (BC), carboxyltransferase (CT), and biotin carboxyl carrier protein (BCCP) domains. The CT domain of UC consists of four subdomains, named A, B, C and D. This domain covers the C and D subdomains of the CT domain. This domain covers the whole length of 5-oxoprolinase … expand

Urea carboxylase (UC) catalyses a two-step, ATP- and biotin-dependent carboxylation reaction of urea. It is composed of biotin carboxylase (BC), carboxyltransferase (CT), and biotin carboxyl carrier protein (BCCP) domains. The CT domain of UC consists of four subdomains, named A, B, C and D. This domain covers the C and D subdomains of the CT domain. This domain covers the whole length of 5-oxoprolinase subunit B (PxpB, originally called KipI (kinase A inhibitor) from Bacillus subtilis [[see IPR010016 PUBMED:9334321 PUBMED:28830929 ]). It can also be found in S. cerevisiae urea amidolyase Dur1,2, which is a multifunctional biotin-dependent enzyme with domains for urea carboxylase and allophanate (urea carboxylate) hydrolase activity [ PUBMED:20884691 ].

PxpB forms a complex with KipA, which is covered by the A and B subdomains of the CT. This complex shares protein structure and sequence similarity with the CT domain of urea amidolyase from K. lactis, but residues that are important for CT catalysis are not conserved in KipA and KipI. Therefore, the PxpB-KipI complex is unlikely to have CT activity [ PUBMED:22869039 ].