Thermal unfolding of the cytotoxin alpha-sarcin: phospholipid binding induces destabilization of the protein structure.
The effect of membrane binding on the structure and stability of the cytotoxin alpha-sarcin has been studied by differential scanning calorimetry, Fourier-transform infrared and fluorescence spectroscopic techniques. The thermal unfolding of alpha-sarcin in aqueous solution fits into a two-state transition characterized by a transition temperature (Tm) of 52.6 degrees C and a calorimetric enthalpy (delta Hcal) of 136 kcal/mol. Upon interaction with phosphatidylglycerol vesicles, alpha-sarcin undergoes conformational changes, as deduced from the FTIR and fluorescence emission spectra. These changes result in a decreased Tm and delta Hcal values for the thermal unfolding of phospholipid-bound alpha-sarcin. The lower Tm value for lipid-bound alpha-sarcin is also observed at the level of secondary and tertiary structures, based on analyses of both the amide I' infrared spectrum and the tryptophan emission of the protein as a function of temperature, respectively. The results obtained indicate a protein destabilization promoted by the phospholipid interaction.
Gasset
M
M
Departamento de Bioquímica y Biología Molecular, Facultad de Química, Universidad Complutense, Madrid, Spain.
Mancheño
J M
JM
Laynez
J
J
Lacadena
J
J
Fernández-Ballester
G
G
Martinez del Pozo
A
A
Oñaderra
M
M
Gavilanes
J G
JG
D000970:Antineoplastic Agents / Q000737:chemistry*; D001230:Aspergillus; D002152:Calorimetry, Differential Scanning; D004722:Endoribonucleases; D005656:Fungal Proteins / Q000737:chemistry*; D006358:Hot Temperature; D010743:Phospholipids / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D011500:Protein Synthesis Inhibitors / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared
D000970:Antineoplastic Agents; D005656:Fungal Proteins; D010743:Phospholipids; D011500:Protein Synthesis Inhibitors; C014801:alpha-sarcin; D004722:Endoribonucleases