Peptides on the Surface. PELDOR Data for Spin-Labeled Alamethicin F50/5 Analogues on Organic Sorbent

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• 作者：Alexander D. Milov ; Rimma I. Samoilova ; Yuri D. Tsvetkov ; Cristina Peggion ; Fernando Formaggio ; Claudio Toniolo
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：June 26, 2014
• 年：2014
• 卷：118
• 期：25
• 页码：7085-7090
• 全文大小：255K
• ISSN：1520-5207

文摘

The PELDOR technique was used to obtain the spectra of distances between spin labels for mono and double TOAC substituted analogues of [Glu(OMe)^7,18,19] alamethicin F50/5 (Alm鈥?/b>) peptaibiotic on the surface of the organic sorbent Oasis HLB and in ethanol solution at 77 K. For the double-labeled Alm鈥?/b>, the free radical probes are at positions 1 and 16 (Alm鈥?/b>1,16). The intra- and intermolecular contributions to the PELDOR time traces were separated, with regard to the fractality of the system studied. We established that on HLB the labeled Alm鈥?/b> molecules are prone to aggregation. The distance spectra for Alm鈥?/b>1,16 show that, in both adsorbed state and in ethanol solution, the peptaibiotic is predominantly folded in the 伪-helix conformation. We assign the asymmetry of the distance spectrum in both cases to the occurrence of an admixture of more elongated 伪/3₁₀-helical conformers. The portion of these conformers is higher for the peptide adsorbed on HLB. We speculate that both the broadening of the basic spectrum line at r_max = 2.0 nm and the increase in the contribution of elongated conformers might be associated with the spread of the peptaibiotic adsorption sites on HLB as compared with the more uniform Alm鈥?/b>1,16 trap structure in frozen ethanol solution. The aggregates of mono-labeled Alm鈥?/b>1 and Alm鈥?/b>16 also studied. The intermolecular distance spectrum for Alm鈥?/b>1 on HLB is shifted toward longer distances as compared with those of Alm鈥?/b>16. This result suggests that in the aggregates Alm鈥?/b> molecules are preferentially oriented with their C-terminal regions in the vicinity.