title: Stabilization of anionic and neutral forms of a fluorophoric ligand at the active site of human carbonic anhydrase I.
abstract: We synthesized a fluorogenic dansylamide derivative (JB2-48), which fills the entire (15 A deep) active site pocket of human carbonic anhydrase I, and investigated the contributions of sulfonamide and hydrophobic regions of the ligand structure on the spectral, kinetic, and thermodynamic properties of the enzyme-ligand complex. The steady-state and fluorescence lifetime data revealed that the deprotonation of the sulfonamide moiety of the enzyme bound ligand increases the fluorescence emission intensity as well as the lifetime of the fluorophores. This is manifested via the electrostatic interaction between the active site resident Zn²+ cofactor and the negatively charged sulfonamide group of the ligand, and such interaction contributes to about 2.2 kcal/mol (ΔΔG°) and 0.89 kcal/mol (ΔΔG(#)) energy in stabilizing the ground and the putative transition states, respectively. We provide evidence that the anionic and neutral forms of JB2-48 are stabilized by the complementary microscopic/conformational states of the enzyme. The implication of the mechanistic studies presented herein in rationale design of carbonic anhydrase inhibitors is discussed.
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58105, USA.
authors.forename: Sumathra
authors.initials: S
authors.lastname: Manokaran
authors.forename: Jayati
authors.initials: J
authors.lastname: Banerjee
authors.forename: Sanku
authors.initials: S
authors.lastname: Mallik
authors.forename: D K
authors.initials: DK
authors.lastname: Srivastava
mesh_terms: D024401:Carbonic Anhydrase I / Q000737:chemistry*; D020134:Catalytic Domain; D003619:Dansyl Compounds / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008024:Ligands; D008956:Models, Chemical; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D003619:Dansyl Compounds; D005456:Fluorescent Dyes; D008024:Ligands; C001026:5-dimethylaminonaphthalene-1-sulfonamide; D024401:Carbonic Anhydrase I