The Specificity and Architecture of the Acyl-CoA Carboxylase Beta Subunit in Streptomyces coelicolor A3(2).

DIACOVICH L., GAGO G., TSAI S-C.(S), KHOSLA C., GRAMAJO H.

San Carlos de Bariloche. Rio Negro.

Congreso; XXXIX Reunion Anual de la Sociedad Argentina de Bioquimica y Biologia Molecular (SAIB), XXXII Annual Meeting. Sociedad Argentina de Biofísica (SAB).; 2003

Sociedad Argentina de Bioquimica y Biologia Molecular y Biophysical Society of Argentina

Two acyl-CoA carboxylase complexes, acetyl-CoA carboxylase (ACC) and propionyl-CoA carboxylase (PCC) have been characterized in Streptomyces coelicolor whose main physiological role appears to be provide malonyl- and methylmalonyl-CoA for both fatty acid and polyketide biosynthesis. Both complexes shared the same biotinylated alpha ƒnsubunit, AccA2 (biotin carboxyl carrier protein, BCCP), that also contains a biotin carboxylase domain. The beta ƒnand the epsilon subunits were specific from each of the complexes (AccB-AccE and PccB-PccE to ACC y PCC respectively). The beta subunit has transcaboxylase activity and epsilon subunit form a subcomplex with the beta subunit increasing drastically the activity of the enzymatic complex. ACC and PCC in S. ceolicolor are 1 MDa multienzyme complexes containing at least 18 polypeptide chains. The b subunit, PccB and AccB are 360 kDa homo-hexamers. Apo and substrate-bound crystal structures of PccB hexamer were solved to 2.0 - 2.4 A. Overall, the hexamer assembly of the core 360 kDa beta ƒnsubunit forms a large ring-shaped complex as two stacks of trimers related by two-fold symmetry. In the active site, oxyanion hole and hydrogen-bonding network were identified. The structural studies shed light on the molecular basis of substrate recognition and the nature of the assembly. Hybrid fusions and mutants of beta subunit of were constructed to analyze the difference on their substrate specificity. The hexameric structure also helps to visualize different oligomeric architectures of ACC and PCC from different organisms, as well as the identification of future drug design targets.