title: Role of inhibitor aliphatic chain in the thermodynamics of inhibitor binding to Escherichia coli enoyl-ACP reductase and the Phe203Leu mutant: a proposed mechanism for drug resistance.
abstract: The antibacterial target enoyl-acyl carrier protein (ACP) reductase is a homotetrameric enzyme that catalyzes the last reductive step of fatty acid biosynthesis. In the present paper, four 2-(2-hydroxyphenoxy)phenol inhibitors, wherein the 4-position substituent varied from H to n-propyl, were studied to determine the contribution of the aliphatic chain to the binding to the wild-type (wt) enoyl-ACP reductase from Escherichia coli (FabI) and a drug-resistant mutant, (F203L)FabI, in which phenylalanine 203 is mutated to leucine. Thermodynamic parameters of ternary complex formation (enzyme-NAD(+)-inhibitor) were determined by isothermal titration calorimetry. The inhibitor affinity to wt FabI and (F203L)FabI increases with increasing aliphatic chain length, although the corresponding affinity for (F203L)FabI is lower, and also, it shows no detectable binding to the 4-H inhibitor. A distinguishing feature of inhibitor binding to either binary enzyme-NAD(+) complex is the apparent negative cooperativity for binding to the tetramer with half-site occupancy. For both enzymes, binding is enthalpy, DeltaH, driven. However, binding DeltaH becomes less favorable with increasing aliphatic chain length. Increases in affinity are found to be exclusively due to favorable changes in solvation entropy. Incremental changes in thermodynamic parameters within the series of inhibitors binding to wt FabI and (F203L)FabI are approximately the same. However, absolute differences between the two enzymes for binding to a given inhibitor are significant, suggesting different binding modes. This finding, coupled with a binding site conformation that is likely to be more rigid in the mutant, appears to result in the drug resistance of (F203L)FabI.
authors.affiliation: Center for Biophysical Sciences and Engineering, University of Alabama at Birmingham, 1025 18th Street South, Birmingham, Alabama 35294, USA.
authors.forename: Irina I
authors.initials: II
authors.lastname: Protasevich
authors.forename: Christie G
authors.initials: CG
authors.lastname: Brouillette
authors.forename: Mark E
authors.initials: ME
authors.lastname: Snow
authors.forename: Steve
authors.initials: S
authors.lastname: Dunham
authors.forename: J Ronald
authors.initials: JR
authors.lastname: Rubin
authors.forename: Rocco
authors.initials: R
authors.lastname: Gogliotti
authors.forename: Karen
authors.initials: K
authors.lastname: Siegel
mesh_terms: D001665:Binding Sites; D002151:Calorimetry; D024881:Drug Resistance, Bacterial / Q000187:drug effects; D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH); D019277:Entropy; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics; D064429:Fatty Acid Synthases / Q000737:chemistry; D006358:Hot Temperature; D007930:Leucine / Q000235:genetics; D010088:Oxidoreductases / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics; D010636:Phenols / Q000737:chemistry / Q000378:metabolism; D010649:Phenylalanine / Q000235:genetics; D017354:Point Mutation; D011487:Protein Conformation; D017510:Protein Folding; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D010636:Phenols; D011994:Recombinant Proteins; D010649:Phenylalanine; D010088:Oxidoreductases; D050753:Enoyl-(Acyl-Carrier-Protein) Reductase (NADH); D064429:Fatty Acid Synthases; D007930:Leucine