title: Thermal unfolding of eosinophil cationic protein/ribonuclease 3: a nonreversible process.
abstract: Eosinophil cationic protein (ECP)/ribonuclease 3 is a member of the RNase A superfamily involved in inflammatory processes mediated by eosinophils. ECP is bactericidal, helminthotoxic, and cytotoxic to tracheal epithelium cells and to several mammalian cell lines although its RNase activity is low. We studied the thermal stability of ECP by fourth-derivative UV absorbance spectra, circular dichroism, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The T (1/2) values obtained with the different techniques were in very good agreement (T (1/2) approximately 72 degrees C), and the stability was maintained in the pH range between 5 and 7. The ECP calorimetric melting curve showed, in addition to the main transition, a pretransitional conformational change with a T (1/2) of 44 degrees C. Both calorimetric transitions disappeared after successive re-heatings, and the ratio DeltaH versus DeltaH (vH) of 2.2 indicated a significant deviation from the two-state model. It was observed that the thermal unfolding was irreversible. The unfolding process gives rise to changes in the environment of aromatic amino acids that are partially maintained in the refolded protein with the loss of secondary structure and the formation of oligomers. From the thermodynamic analysis of ECP variants, the contribution of specific amino acids, such as Trp10 and the region 115-122, to thermal stability was also determined. The high thermal stability of ECP may contribute to its resistance to degradation when the protein is secreted to the extracellular medium during the immune response.
authors.affiliation: Unitat de Bioquímica, Facultat de Ciències, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.
authors.forename: Zoran
authors.initials: Z
authors.lastname: Nikolovski
authors.forename: Víctor
authors.initials: V
authors.lastname: Buzón
authors.forename: Marc
authors.initials: M
authors.lastname: Ribó
authors.forename: Mohammed
authors.initials: M
authors.lastname: Moussaoui
authors.forename: Maria
authors.initials: M
authors.lastname: Vilanova
authors.forename: Claudi M
authors.initials: CM
authors.lastname: Cuchillo
authors.forename: Josep
authors.initials: J
authors.lastname: Cladera
authors.forename: M Victòria
authors.initials: MV
authors.lastname: Nogués
mesh_terms: D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism / Q000379:methods; D004220:Disulfides / Q000737:chemistry; D004795:Enzyme Stability; D047150:Eosinophil Cationic Protein / Q000737:chemistry*; D006801:Humans; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry; D011489:Protein Denaturation; D017510:Protein Folding; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013057:Spectrum Analysis; D013696:Temperature; D013816:Thermodynamics
chemical_list: D004220:Disulfides; D050505:Mutant Proteins; D047150:Eosinophil Cationic Protein