Stability against temperature of Sulfolobus solfataricus elongation factor 1α, a multi-domain protein

The elongation factors (EF-Tu/EF-1α) are universal proteins, involved in protein biosynthesis. A detailed characterization of the stability against temperature of SsEF-1α, a three-domain protein isolated from the hyperthermophilic archaeon Sulfolobus solfataricus is presented. Thermal denaturation of both the GDP-bound (SsEF-1α
- GDP) and the ligand-free (nfSsEF-1α) forms was investigated by means of circular dichroism and fluorescence measurements, over the 4.0-7.5 pH interval. Data indicate that the unfolding process is cooperative with no intermediate species and that the few inter-domain contacts identified in the crystal structure of SsEF-1α play a role also at high temperatures. Finally, it is shown that the enzyme exhibits two different interchangeable thermally denatured states, depending on pH.