title: Crystal structures and mutational analyses of acyl-CoA carboxylase beta subunit of Streptomyces coelicolor.
abstract: The first committed step of fatty acid and polyketides biosynthesis, the biotin-dependent carboxylation of an acyl-CoA, is catalyzed by acyl-CoA carboxylases (ACCases) such as acetyl-CoA carboxylase (ACC) and propionyl-CoA carboxylase (PCC). ACC and PCC in Streptomyces coelicolor are homologue multisubunit complexes that can carboxylate different short chain acyl-CoAs. While ACC is able to carboxylate acetyl-, propionyl-, or butyryl-CoA with approximately the same specificity, PCC only recognizes propionyl- and butyryl-CoA as substrates. How ACC and PCC have such different specificities toward these substrates is only partially understood. To further understand the molecular basis of how the active site residues can modulate the substrate recognition, we mutated D422, N80, R456, and R457 of PccB, the catalytic beta subunit of PCC. The crystal structures of six PccB mutants and the wild type crystal structure were compared systematically to establish the sequence-structure-function relationship that correlates the observed substrate specificity toward acetyl-, propionyl-, and butyryl-CoA with active site geometry. The experimental data confirmed that D422 is a key determinant of substrate specificity, influencing not only the active site properties but further altering protein stability and causing long-range conformational changes. Mutations of N80, R456, and R457 lead to variations in the quaternary structure of the beta subunit and to a concomitant loss of enzyme activity, indicating the importance of these residues in maintaining the active protein conformation as well as a critical role in substrate binding.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR-Consejo Nacional de Investigaciones Científicas y Técnicas) and Departamento de Microbiología, Facultad de Ciencias Bioquímicasy Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina.
authors.forename: Ana
authors.initials: A
authors.lastname: Arabolaza
authors.forename: Mary Elizabeth
authors.initials: ME
authors.lastname: Shillito
authors.forename: Ting-Wan
authors.initials: TW
authors.lastname: Lin
authors.forename: Lautaro
authors.initials: L
authors.lastname: Diacovich
authors.forename: Melrose
authors.initials: M
authors.lastname: Melgar
authors.forename: Huy
authors.initials: H
authors.lastname: Pham
authors.forename: Deborah
authors.initials: D
authors.lastname: Amick
authors.forename: Hugo
authors.initials: H
authors.lastname: Gramajo
authors.forename: Shiou-Chuan
authors.initials: SC
authors.lastname: Tsai
mesh_terms: D000105:Acetyl Coenzyme A / Q000235:genetics / Q000378:metabolism; D000103:Acetyl-CoA Carboxylase / Q000235:genetics / Q000378:metabolism; D000214:Acyl Coenzyme A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001710:Biotin / Q000235:genetics / Q000378:metabolism; D019735:Carbon-Carbon Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D005838:Genotype; D043586:Methylmalonyl-CoA Decarboxylase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D048372:Streptomyces coelicolor / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity / Q000235:genetics
chemical_list: D000214:Acyl Coenzyme A; C024343:butyryl-coenzyme A; C009061:propionyl-coenzyme A; D001710:Biotin; D000105:Acetyl Coenzyme A; D019735:Carbon-Carbon Ligases; C018757:acyl-CoA carboxylase; D000103:Acetyl-CoA Carboxylase; C022458:propionyl CoA carboxylase (ATP-hydrolyzing); D043586:Methylmalonyl-CoA Decarboxylase