Contribution of fluorine to protein-ligand affinity in the binding of fluoroaromatic inhibitors to carbonic anhydrase II

Carbonic anhydrase II (CAII) is a zinc metalloenzyme that catalyzes the hyd ration of CO2 to yield bicarbonate and a proton. N-(4-Sulfamylbenzoyl)benzy lamine (SBB) is a tight-binding inhibitor of human CAII with K-d = 2.1 nM. Previous X-ray crystallographic work shows that the benzyl ring of SBB make s an edge-to-face interaction with Phe-131 in the enzyme active site. We ha ve manipulated the electrostatics of this interaction by systematically sub stituting electronegative fluorine atoms for the benzyl ring hydrogens of S BB. Crystal structures of 10 enzyme-inhibitor complexes have been determine d to atomic resolution. Analysis of these structures reveals that the main contributions to enzyme-inhibitor affinity can be approximated by a combina tion of dipole-induced dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. Surprisingly, different electrostatic components dominate af finity in different enzyme-inhibitor pairs.