Residues involved in the catalytic mechanism and substrate specificity of the beta subunit in acil-coA carboxylases of S. coelicolor

ARABOLAZA A, DIACOVICH L., GAGO G., AND GRAMAJO H.

Pinamar, Argentina

Congreso; XLI Reunión Anual de la Sociedad Argentina de Bioquímica y Biología Molecular (SAIB). X Congreso PABMB. Panamerican Association for Biochemistry and Molelucar Biology; 2005

RESIDUES INVOLVED IN THE CATALYTIC MECHANISM AND SUBSTRATE SPECIFICITY OF THE B SUBUNIT IN ACIL-CoA CARBOXYLASES OF S. coelicolor A. Arabolaza, L. Diacovich, G. Gago, and H. Gramajo. Facultad de Ciencias Bioquimicas y Farmaceuticas- IBR, UNR-CONICET, Suipacha 531, Rosario, 2000. Argentina. E-mail: arabolaza@gmail.com Acetyl-CoA carboxylase (ACC) and propionyl-CoA carboxylase (PCC) of Streptomyces coelicolor are multisubunit complexes. Each complex consist of three different subunits a, b y e. Both complexes share the same biotinylated ƒnsubunit a, AccA2. The b and the e subunits are specific from each of the complexes (AccB-AccE and PccB-PccE to ACC y PCC respectively). ACC and PCC catalyze the carboxylation of acetyl- and propionyl-CoA to generate malonyl- and methylmalonyl-CoA, respectively. The core catalytic b ƒnƒnsubunits, PccB and AccB, catalyze the transcarboxylation between carboxi-biotin and acyl-CoAs. The crystal structure of Apo and substrate-bound PccB showed a hydrophobic and highly conserved biotin-binding pocket. Biotin and propionyl-CoA bind perpendicular to each other in the active site, where two oxyanion holes were identified. N1 of biotin is proposed to be the active site base. Based on the amino acid sequence alignment and structure comparison between AccB and PccB we identify some key residues. The molecular basis of substrate specificity and the essentiality of oxyanions hole was investigated by mutagenesis. Understanding the substrate specificity of ACC and PCC will help to develop novel structure-based inhibitors that are potential therapeutics against infectious disease. It would also facilitate bioengineering to provide novel extender units for polyketide biosynthesis.