The eubacterial protein synthesis inhibitor pulvomycin interacts with archaeal elongation factor 1?? from Sulfolobus solfataricus

The effect of pulvomycin on the biochemical and fluorescence spectroscopic properties of the archaeal elongation factor 1?? from Sulfolobus solfataricus (SsEF-1??), the functional analog of eubacterial EF-Tu, was investigated. The antibiotic was able to reduce in vitro the rate of protein synthesis however, the concentration of pulvomycin leading to 50% inhibition (173 ??M) was two order of magnitude higher but one order lower than that required in eubacteria and eukarya, respectively. The effect of the antibiotic on the partial reactions catalysed by SsEF-1?? indicated that pulvomycin was able to decrease the affinity of the elongation factor toward aa-tRNA only in the presence of GTP, to an extent similar to that measured in the presence of GDP. Moreover, the antibiotic produced an increase of the intrinsic GTPase catalysed by SsEF-1??, but not that of its engineered forms. Finally, pulvomycin induced a variation in fluorescence spectrum of the aromatic region of the elongation factor and its truncated forms. These spectroscopic results suggested that a conformational change of the elongation factor takes place upon interaction with the antibiotic. This finding was confirmed by the protection against chemical denaturation of SsEF-1??, observed in the presence of pulvomycin. However, a stabilising effect of the antibiotic directly on the protein in the complex could takes place.