Thermodynamics of target peptide recognition by calmodulin and a calmodulin analogue: implications for the role of the central linker

The thermodynamics of interaction of two model peptides melittin and mastop aran with bovine brain calmodulin (CAM) and a smaller CAM analogue, a calci um binding protein front Entamoeba histolytica (CaBP) in 10 mM MOPS buffer (pH 7.0) was examined using isothermal titration calorimetry (ITC), These d ata show that CAM binds to both the peptides and the enthalpy of binding is endothermic for melittin and exothermic for mastoparan at 25 degrees C. Ca BP binds to the longer peptide melittin, but does not bind to mastoparan, t he binding enthalpy being endothermic in nature. Concurrently, we also obse rve a larger increase in alpha-helicity upon the binding of melittin to CAM when compared to CaBP, The role of hydrophobic interactions in the binding process has also been examined using 8-anilino-1-naphthalene-sulphonic aci d (ANS) binding monitored by ITC, These results have been employed to ratio nalize the energetic consequences of the binding reaction. (C) 1999 Federat ion of European Biochemical Societies.