Influence of active site ligands and nanoparticle surfaces on human carbonic anhydrase isozymes

Carbonic anhydrase (CA) is an ubiquitously distributed zinc containing metallo enzyme that catalyzes the reversible hydration of carbon dioxide to form bicarbonate and a proton. Due to their involvement in many pathological processes, CA isozymes have been the target for drug designing for the past 6 decades. The present study was designed with the aim of understanding the effect of active site ligands and nanoparticle surfaces on human carbonic anhydrase isozymes.;In an effort to identify a fluorescent probe for carbonic anhydrases, the quantum yields and binding affinities of a variety of naphthalenesulfonamide derivatives with human carbonic anhydrase isozymes (hCAs) were determined. In this pursuit, a highly sensitive fluorescent probe, JB2-48 was identified and the contributions of its sulfonamide moiety and the hydrophobic regions on the spectral, kinetic, and thermodynamic properties of the enzyme-ligand complex have been investigated. The fluorescence 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 ligand. This is manifested via the electrostatic interaction between the active site resident Zn 2+ cofactor and the negatively charged sulfonamide group of the ligand.;Investigations on the binding of the sulfonamide inhibitor, benzene sulfonamide (BS), with hCA isozymes II and VII, revealed that the binding is stabilized by polar interactions in the former case and hydrophobic interactions in the latter case. In addition, it was found that the binding of BS with hCA II is enthalpically driven at low temperatures, whereas it is entropically driven for its binding with hCA VII.;Investigation on the effects of the interaction of differently charged quantum dots, liposomes and polylysine on hCA XII revealed that these charged particles differently modulated the active site of the enzyme. The data revealed that whereas polylysine and liposomes exhibited no influence on the binding and catalytic features of the enzyme, quantum dots had significant influence on the above features. Arguments were presented that the above differential feature exhibited by quantum dots, liposomes and polylysine is encoded in the rigidity versus flexibility of the charged molecules.