Component of a biotin-dependent acyl-CoA carboxylase complex. This subunit transfers the CO2 from carboxybiotin to the CoA ester substrate (PubMed:16354663, PubMed:28222482). When associated with the alpha3 subunit AccA3, the beta5 subunit AccD5 and the epsilon subunit AccE5, forms the LCC complex, which is involved in the carboxylation of long chain acyl-CoA (PubMed:16354663, PubMed:28222482). The LCC complex can use C16-C24 substrates, the highest specific activity is obtained with carboxy-C20-CoA (PubMed:28222482). Has low activity with acetyl-CoA and propionyl-CoA (PubMed:16354663). The biotin-dependent long-chain acyl-CoA carboxylase (LCC) complex is composed of AccA3, which contains the biotin carboxylase (BC) and biotin carboxyl carrier protein (BCCP) domains, and AccD4, which contains the carboxyl transferase (CT) domain (PubMed:16354663, PubMed:28222482). The complex also contains the beta5 subunit AccD5 and the epsilon subunit 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.