Sodium Dodecyl Sulfate Monomers Induce XAO Peptide Polyproline II to 伪-Helix Transition

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• 作者：Zhenmin Hong ; Krishnan Damodaran ; Sanford A. Asher
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：September 11, 2014
• 年：2014
• 卷：118
• 期：36
• 页码：10565-10575
• 全文大小：564K
• ISSN：1520-5207

文摘

XAO peptide (Ac鈥揦₂A₇O₂鈥揘H₂; X: diaminobutyric acid side chain, 鈭扖H₂CH₂NH₃⁺; O: ornithine side chain, 鈭扖H₂CH₂CH₂NH₃⁺) in aqueous solution shows a predominantly polyproline II (PPII) conformation without any detectable 伪-helix-like conformations. Here we demonstrate by using circular dichroism (CD), ultraviolet resonance Raman (UVRR) and nuclear magnetic resonance (NMR) spectroscopy that sodium dodecyl sulfate (SDS) monomers bind to XAO and induce formation of 伪-helix-like conformations. The stoichiometry and the association constants of SDS and XAO were determined from the XAO鈥揝DS diffusion coefficients measured by pulsed field gradient NMR. We developed a model for the formation of XAO鈥揝DS aggregate 伪-helix-like conformations. Using UVRR spectroscopy, we calculated the Ramachandran 蠄 angle distributions of aggregated XAO peptides. We resolved 伪-, 蟺- and 3₁₀- helical conformations and a turn conformation. XAO nucleates SDS aggregation at SDS concentrations below the SDS critical micelle concentration. The XAO₄鈥揝DS₁₆ aggregates have four SDS molecules bound to each XAO to neutralize the four side chain cationic charges. We propose that the SDS alkyl chains partition into a hydrophobic core to minimize the hydrophobic area exposed to water. Neutralization of the flanking XAO charges enables 伪-helix formation. Four XAO鈥揝DS₄ aggregates form a complex with an SDS alkyl chain-dominated hydrophobic core and a more hydrophilic shell where one face of the 伪-helix peptide contacts the water environment.