Component of a biotin-dependent acyl-CoA carboxylase complex. This subunit transfers the CO2 from carboxybiotin to the CoA ester substrate. When associated with the alpha3 subunit AccA3, is involved in the carboxylation of acetyl-CoA and propionyl-CoA. 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] Lipid metabolism; mycolic acid biosynthesis. 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. Belongs to the AccD/PCCB family.