Component of a biotin-dependent acyl-CoA carboxylase complex. This subunit transfers the CO2 from carboxybiotin to the CoA ester substrate (PubMed:16354663, PubMed:16385038, PubMed:28222482). When associated with the alpha3 subunit AccA3, is involved in the carboxylation of acetyl-CoA and propionyl-CoA, with a preference for propionyl-CoA (PubMed:16354663, PubMed:16385038, PubMed:28222482). Is also required for the activity of the long-chain acyl-CoA carboxylase (LCC) complex (PubMed:28222482). acetyl-CoA + N(6)-carboxybiotinyl-L-lysyl-[protein] = malonyl-CoA + N(6)-biotinyl-L-lysyl-[protein] N(6)-carboxybiotinyl-L-lysyl-[protein] + propanoyl-CoA = methylmalonyl-CoA + N(6)-biotinyl-L-lysyl-[protein] Carboxylase activity of the AccA3/AccD5 complex is stimulated by interaction with AccE5. Lipid metabolism; mycolic acid biosynthesis. Forms homohexamers (PubMed:16492739, PubMed:17157300). The biotin-dependent acyl-CoA carboxylase complex is composed of AccA3, which contains the biotin carboxylase (BC) and biotin carboxyl carrier protein (BCCP) domains, and AccD5, which contains the carboxyl transferase (CT) domain (PubMed:16354663, PubMed:16385038). The AccA3/AccD5 complex forms a dodecamer, and can associate with the epsilon subunit AccE5 (Rv3280), which stimulates carboxylation by the complex (PubMed:16354663, PubMed:16385038). Is also part of the long-chain acyl-CoA carboxylase (LCC) complex, which is composed of AccA3, AccD4, AccD5 and AccE5. The four subunits are essential for activity, but AccD5, together with AccE5, probably plays a structural role rather than a catalytic one (PubMed:28222482). Expressed at higher levels during the exponential growth phase. Belongs to the AccD/PCCB family.