Structure of the biotin carboxylase domain of pyruvate carboxylase from Bacillus thermodenitrificans

The biotin carboxylase (BC) domain of pyruvate carboxylase (PC) from Bacillus thermodenitrificans (BC-bPC) was crystallized in an orthorhombic form (space group P2₁2₁2₁), with unit-cell parameters a = 79.6, b = 116.0, c = 115.7 Å. Two BC protomers are contained in the asymmetric unit. Diffraction data were collected at 100 K and the crystal structure was solved by the molecular-replacement method and refined against reflections in the 20.0-2.4 Å resolution range, giving an R factor of 0.235 and a free R factor of 0.292. The overall structure of BC-bPC is similar to those of the BC subunits of Aquifex aeolicus PC (BC-aPC) and Escherichia coli ACC (BC-­eACC). The crystal structure revealed that BC-bPC forms a unique dimeric quaternary structure, which might be caused as a result of the division of the BC domain from the rest of the protein. The position of domain B in BC-bPC differs from those in other enzymes of similar structure (BC-­aPC and BC-eACC).