Thermodynamic and circular dichroism studies differentiate inhibitor interactions with the stromelysin S(1)-S(3) and...

Interactions of stromelysin with a series of inhibitors representative of three chemical templates with distinct binding modes were examined. Unfolding temperatures for inhibitor complexes were 10 degrees C to 15 degrees C greater than for apo stromelysin. Minor changes in ellipticity in the far-UV CD spectra of complexes indicated that ligand-induced conformational changes were localized to the binding site and did not involve gross changes in protein folding. Isothermal titrating calorimetry of thiadiazole-containing inhibitors, which bind in the S(1)-S(3) subsites of stromelysin, indicated that the binding interaction was exothermic and only slightly favorable entropically. Near-UV CD spectra showed large positive ellipticity increases from 250 to 300 nm, consistent with an interaction between the benzene ring of the inhibitor and stromelysin residues Tyr155 and Tyr168. Interactions between stromelysin and amide-hydroxamate ligands, which bind in the S(')(1)-S(')(3) subsites, were found to be both enthalpically and entropically driven. Binding of this class of ligands resulted in modest negative ellipticity changes at 260-285 nm and positive increases at 292 nm. Stromelysin complexed to a lactam-hydroxamate inhibitor with structure extending into both the S(1)-S(3) and S(')(1)-S(')(3) subsites showed increased ellipticity at 245 nm and negative changes at 260-285 and 295 nm.