title: Crystal structure of class I acetohydroxy acid isomeroreductase from Pseudomonas aeruginosa.
abstract: Acetohydroxy acid isomeroreductase (AHIR) is a key enzyme in the biosynthesis of branched-chain amino acids. We have determined the first crystal structure of a class I AHIR from Pseudomonas aeruginosa at 2.0 A resolution. Its dodecameric architecture of 23 point group symmetry is assembled of six dimeric units and dimerization is essential for the formation of the active site. The dimeric unit of P.aeruginosa AHIR partially superimposes with a three-domain monomer of spinach AHIR, a class II enzyme. This demonstrates that the so-called plant-specific insert in the middle of spinach AHIR is structurally and functionally equivalent to the C-terminal alpha-helical domain of P.aeruginosa AHIR, and the C-terminal alpha-helical domain was duplicated during evolution from the shorter, class I AHIRs to the longer, class II AHIRs. The dimeric unit of P.aeruginosa AHIR possesses a deep figure-of-eight knot, essentially identical with that in the spinach AHIR monomer. Thus, our work lowers the likelihood of the previous proposal that "domain duplication followed by exchange of a secondary structure element can be a source of such a knot in the protein structure" being correct.
authors.affiliation: Structural Proteomics Laboratory, School of Chemistry and Molecular Engineering, College of Natural Sciences, Seoul National University, Seoul 151742, South Korea.
authors.forename: Hyung Jun
authors.initials: HJ
authors.lastname: Ahn
authors.forename: Su Jung
authors.initials: SJ
authors.lastname: Eom
authors.forename: Hye-Jin
authors.initials: HJ
authors.lastname: Yoon
authors.forename: Byung Il
authors.initials: BI
authors.lastname: Lee
authors.forename: Hyeongjin
authors.initials: H
authors.lastname: Cho
authors.forename: Se Won
authors.initials: SW
authors.lastname: Suh
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000378:metabolism; D019143:Evolution, Molecular; D050540:Ketol-Acid Reductoisomerase; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009249:NADP / Q000378:metabolism; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000201:enzymology* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D009249:NADP; D000429:Alcohol Oxidoreductases; D050540:Ketol-Acid Reductoisomerase; D008274:Magnesium