Residual ligand entropy in the binding of p-substituted benzenesulfonamide ligands to bovine carbonic anhydrase II.
In studies on the thermodynamics of ligand-protein interactions, it is often assumed that the configurational and conformational entropy of the ligand is zero in the bound state (i.e., the ligand is rigidly fixed in the binding pocket). However, there is little direct experimental evidence for this assumption, and in the case of binding of p-substituted benzenesulfonamide inhibitors to bovine carbonic anhydrase II (BCA II), the observed thermodynamic binding signature derived from isothermal titration calorimetry experiments leads indirectly to the conclusion that a considerable degree of residual entropy remains in the bound ligand. Specifically, the entropy of binding increases with glycine chain length n, and strong evidence exists that this thermodynamic signature is not driven by solvent reorganization. By use of heteronuclear (15)N NMR relaxation measurements in a series (n = 1-6) of (15)N-glycine-enriched ligands, we find that the observed thermodynamic binding signature cannot be explained by residual ligand dynamics in the bound state, but rather results from the indirect influence of ligand chain length on protein dynamics.
Stöckmann
Henning
H
Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.
Bronowska
Agnieszka
A
Syme
Neil R
NR
Thompson
Gary S
GS
Kalverda
Arnout P
AP
Warriner
Stuart L
SL
Homans
Steve W
SW
D000818:Animals; D024402:Carbonic Anhydrase II / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D018360:Crystallography, X-Ray; D019277:Entropy; D007546:Isoquinolines / Q000138:chemical synthesis / Q000737:chemistry; D008024:Ligands; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D013449:Sulfonamides / Q000737:chemistry*; D000096926:Benzenesulfonamides
D024402:Carbonic Anhydrase II; D007546:Isoquinolines; D008024:Ligands; D013449:Sulfonamides; D000096926:Benzenesulfonamides