<p> Biotin-dependent carboxylase enzymes perform a two step reaction. Enzyme-boundbiotin is first carboxylated by bicarbonated and ATP and the carboxyl grouptemporarily bound to biotin is subsequently transferred to an acceptorsubstrate such as pyruvate or acetyl-CoA. The first step is mediated by the BCdomain common to all biotin-dependent carboxylases [<cite idref="PUB00015350"/>]. The BC domain can bedivided in three subdomains (N-terminal, central and C-terminal). TheN-terminal region provides part of the active site; the central regioncorresponds to the ATP-grasp domain, which is common to manyATP-dependent enzymes involved in macromolecular synthesis [<cite idref="PUB00015348"/>]. The ATP-graspmodule directly binds the ATP molecule. The C-terminal subdomain is involvedin dimer formation.</p><p>Several structure of the BC domain have been solved [<cite idref="PUB00015349"/>, <cite idref="PUB00014226"/>]. The central module is splayed significantly away from themain body of the domain and is able to rotate of approximately 45 degree uponnucleotide binding thereby closing off the active site pocket [<cite idref="PUB00014226"/>].</p> Biotin carboxylation domain