Thermodynamic and circular dichroism studies differentiate inhibitor interactions with the stromelysin S-1-S-3 and S-1 '-S-3 ' subsites

Interactions of stromelysin with a series of inhibitors representative of t hree chemical templates with distinct binding modes were examined. Unfoldin g temperatures for inhibitor complexes were 10 degrees C to 15 degrees C gr eater than for apo stromelysin. Minor changes in ellipticity in the far-UV CD spectra of complexes indicated that ligand-induced conformational change s were localized to the binding site and did not involve gross changes in p rotein folding. Isothermal titrating calorimetry of thiadiazole-containing inhibitors, which bind in the S-1-S-3 subsites of stromelysin, indicated th at the binding interaction was exothermic and only slightly favorable entro pically. Near-UV CD spectra showed large positive ellipticity increases fro m 250 to 300 nm, consistent with an interaction between the benzene ring of the inhibitor and stromelysin residues Tyr155 and Tyr168. Interactions bet ween stromelysin and amide-hydroxamate ligands, which bind in the S'(1)-S'( 3) subsites, were found to be both enthalpically and entropically driven. B inding of this class of ligands resulted in modest negative ellipticity cha nges 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 n egative changes at 260-285 and 295 nm. (C) 1999 Elsevier Science B.V. All r ights reserved.