title: The mechanism of aconitase: 1.8 A resolution crystal structure of the S642a:citrate complex.
abstract: The crystal structure of the S642A mutant of mitochondrial aconitase (mAc) with citrate bound has been determined at 1.8 A resolution and 100 K to capture this binding mode of substrates to the native enzyme. The 2.0 A resolution, 100 K crystal structure of the S642A mutant with isocitrate binding provides a control, showing that the Ser --> Ala replacement does not alter the binding of substrates in the active site. The aconitase mechanism requires that the intermediate product, cis-aconitate, flip over by 180 degrees about the C alpha-C beta double bond. Only one of these two alternative modes of binding, that of the isocitrate mode, has been previously visualized. Now, however, the structure revealing the citrate mode of binding provides direct support for the proposed enzyme mechanism.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Lloyd
authors.forename: H
authors.initials: H
authors.lastname: Lauble
authors.forename: G S
authors.initials: GS
authors.lastname: Prasad
authors.forename: C D
authors.initials: CD
authors.lastname: Stout
mesh_terms: D000154:Aconitate Hydratase / Q000737:chemistry* / Q000235:genetics; D019343:Citric Acid / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000737:chemistry; D007523:Isocitrates / Q000737:chemistry*; D008928:Mitochondria / Q000737:chemistry*; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D007523:Isocitrates; D011994:Recombinant Proteins; D019343:Citric Acid; C034219:isocitric acid; D000154:Aconitate Hydratase