IDENTIFICATION OF 2 HYDROPHOBIC PATCHES IN THE ACTIVE-SITE CAVITY OF HUMAN CARBONIC-ANHYDRASE-II BY SOLUTION-PHASE AND SOLID-STATE STUDIES AND THEIR USE IN THE DEVELOPMENT OF TIGHT-BINDING INHIBITOR

This paper describes inhibitors for human carbonic anhydrase II (HCAII , EC 4.2.1.1) that bind with nanomolar dissociation constants. These i nhibitors were developed by exploiting interactions with hydrophobic ' 'patches'' in the lip of the active site of this enzyme. These patches are molecular surfaces presented by a phenylalanine on one face of th e active-site cleft (Phe-131) and three adjacent hydrophobic residues on the opposite face (Leu-198 and Pro-201/202). Comparison of the affi nities of molecules that can occupy either one or both of the two site s indicates that these hydrophobic interactions can contribute factors of 10(2)-10(3) to binding constants and that the strength of the inte raction is relatively insensitive to the structure of the hydrophobic ligand. One of these inhibitors, the competitive inhibitor [N-(4-sulfa moylbenzoyl)phenylglycyl]glycyl]glycine benzyl ester (17), has been st udied by X-ray crystallographic methods in its complex with HCAII at 1 .9-Angstrom resolution. The geometry of binding of the arylsulfonamide group of 17 is similar to geometries observed in other HCAII arylsulf onamide complexes. The aromatic side chain of the phenylglycine residu e of the inhibitor is inferred to pack against the hydrophobic Phe-131 face, and this interaction ''steers'' the peptide backbone of the inh ibitor toward a region in the HCAII active site different from that oc cupied in the related triglycylpeptide. At-tempts to design inhibitors capable of binding simultaneously to Phe-131 and Leu-198/Pro-201/202 did not lead to molecules that-bound more tightly than those binding t o these hydrophobic sites individually.