Thermal-induced changes in the secondary conformation of superoxide dismutase containing different metal ions.
The thermal stability of three superoxide dismutases (SODs) with different metal ions (Mn, Cu/Zn, Fe) in the solid state was studied by a Fourier transform infrared (FT-IR) microspectroscopy combined with thermal analyzer. The IR spectra showed a maximum peak at 1652 cm(-1) for all the native SODs in the amide I band, suggesting a predominant random coil with less alpha-helix structures. By heating each sample, a shoulder at 1631 cm(-1) in the amide I band gradually appeared from 45 degrees C for Fe SOD and from 50 degrees C for Mn SOD but another shoulder at 1639 cm(-1) appeared from 50 degrees C for Cu/Zn SOD. The peak at 1631 cm(-1) is due to the intermolecular beta-sheet structure, but the peak at 1639 cm(-1) corresponds to the major intramolecular beta-sheet with less random coil structure. This reveals that in the first heating process the transformation from random coil/alpha-helix structure to beta-sheet structure initiated from around 45-50 degrees C. There was about 16-22% compositional change resulting from that transformation. However, both additional shoulders stood there and did not restore to their original spectra even with cooling to room temperature, suggesting the denaturation and irreversible properties of the solid SODs after heating. The thermal-dependent denaturation and irreversibility of Mn SOD, Cu/Zn SOD and Fe SOD were clearly evidenced by the increase in intramolecular and intermolecular beta-sheet structure.
Chang
Ching-Hsin
CH
Department of Medical Research and Education, Veterans General Hospital-Taipei, Taipei, Republic of China. sylin@vghtpe.gov.tw
Lin
Shan-Yang
SY
Tsai
Yi-Hung
YH
D000818:Animals; D002417:Cattle; D004926:Escherichia coli / Q000201:enzymology; D006358:Hot Temperature; D007477:Ions; D008670:Metals / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013482:Superoxide Dismutase / Q000737:chemistry*; D013696:Temperature
D007477:Ions; D008670:Metals; D013482:Superoxide Dismutase