title: Cofactor-induced conformational rearrangements establish a catalytically competent active site and a proton relay conduit in FabG.
abstract: beta-Ketoacyl-acyl carrier protein reductase (FabG) is a key component in the type II fatty acid synthase system. The structures of Escherichia coli FabG and the FabG[Y151F] mutant in binary complexes with NADP(H) reveal that mechanistically important conformational changes accompany cofactor binding. The active site Ser-Tyr-Lys triad is repositioned into a catalytically competent constellation, and a hydrogen bonded network consisting of ribose hydroxyls, the Ser-Tyr-Lys triad, and four water molecules creates a proton wire to replenish the tyrosine proton donated during catalysis. Also, a disordered loop in FabG forms a substructure in the complex that shapes the entrance to the active site. A key observation is that the nicotinamide portion of the cofactor is disordered in the FabG[Y151F].NADP(H) complex, and Tyr151 appears to be necessary for high-affinity cofactor binding. Biochemical data confirm that FabG[Y151F] is defective in NADPH binding. Finally, structural changes consistent with the observed negative cooperativity of FabG are described.
authors.affiliation: Department of Structural Biology, St Jude Children's Research Hospital, Memphis, TN 38105 USA.
authors.forename: Allen C
authors.initials: AC
authors.lastname: Price
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Zhang
authors.forename: Charles O
authors.initials: CO
authors.lastname: Rock
authors.forename: Stephen W
authors.initials: SW
authors.lastname: White
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology; D009249:NADP / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011522:Protons
chemical_list: D011522:Protons; D009249:NADP; D000429:Alcohol Oxidoreductases; C023744:acetoacetyl-CoA reductase; D002118:Calcium