title: Salts induce structural changes in elongation factor 1alpha from the hyperthermophilic archaeon Sulfolobus solfataricus: a Fourier transform infrared spectroscopic study.
abstract: Elongation factor 1alpha from the hyperthermophilic archaeon Sulfolobus solfataricus (SsEF-1alpha) carries the aminoacyl tRNA to the ribosome; it binds GDP or GTP, and it is also endowed with an intrinsic GTPase activity that is triggered in vitro by NaCl at molar concentrations [Masullo, M., De Vendittis, E., and Bocchini, V. (1994) J. Biol. Chem. 269, 20376-20379]. The structural properties of SsEF-1alpha were investigated by Fourier transform infrared spectroscopy. The estimation of the secondary structure of the SsEF-1alpha*GDP complex, made by curve fitting of the amide I' band or by factor analysis of the amide I band, indicated a content of 34-36% alpha-helix, 35-40% beta-sheet, 14-19% turn, and 7% unordered structure. The substitution of the GDP bound with the slowly hydrolyzable GTP analogue Gpp(NH)p induced a slight increase in the alpha-helix and beta-sheet content. On the other hand, the alpha-helix content of the SsEF-1alpha*GDP complex increased upon addition of salts, and the highest effect was produced by 5 M NaCl. The thermal stability of the SsEF-1alpha*GDP complex was significantly reduced when the GDP was replaced with Gpp(NH)p or in the presence of NaBr or NH4Cl, whereas a lower destabilizing effect was provoked by NaCl and KCl. Therefore, the extent of the destabilizing effect of salts depended on the nature of both the cation and the anion. The data suggested that the sodium ion was responsible for the induction of the GTPase activity, whereas the anion modulated the enzymatic activity through destabilization of particular regions of SsEF-1alpha. Finally, the infrared data suggested that, in particular region(s) of the polypeptide chain, the SsEF-1alpha*Gpp(NH)p complex possesses structural conformations which are different from those present in the SsEF-1alpha*GDP complex.
authors.affiliation: Istituto di Biochimica, Facoltà di Scienze Matematiche, Fisiche e Naturali, Università degli Studi di Ancona, Via Ranieri, I-60131 Ancona, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Tanfani
authors.forename: A
authors.initials: A
authors.lastname: Scirè
authors.forename: M
authors.initials: M
authors.lastname: Masullo
authors.forename: G
authors.initials: G
authors.lastname: Raimo
authors.forename: E
authors.initials: E
authors.lastname: Bertoli
authors.forename: V
authors.initials: V
authors.lastname: Bocchini
mesh_terms: D000838:Anions / Q000737:chemistry; D001665:Binding Sites; D002412:Cations / Q000737:chemistry; D003461:Crystallography; D006150:Guanine Nucleotides / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000737:chemistry*; D020648:Peptide Elongation Factor 1 / Q000737:chemistry* / Q000302:isolation & purification; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D012965:Sodium Chloride / Q000494:pharmacology*; D017550:Spectroscopy, Fourier Transform Infrared; D016944:Sulfolobus / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000838:Anions; D002412:Cations; D006150:Guanine Nucleotides; D020648:Peptide Elongation Factor 1; D006153:Guanosine Diphosphate; D012965:Sodium Chloride