School of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
J Am Chem Soc. 2011 May 18;133(19):7300-3. doi: 10.1021/ja201349g. Epub 2011 Apr 26.
The effects of chloride and sulfate salts of tetrapropylammonium (TPA(+)) and guanidinium (Gdm(+)) on the conformational stabilities of tryptophan zipper (trpzip) and α-helical (alahel) peptides were measured by circular dichroism spectroscopy. Like Gdm(+), TPA(+) interacts with the planar tryptophan indole group, perturbing the conformational stability of trpzip peptides. TPA(+) effects are largely unaffected by sulfate, indicating an absence of the heteroion pairing that is observed in concentrated Gdm(2)SO(4) solutions. TPA(+) stabilizes helical conformations in alahel peptides, indicating exclusion from the peptide bond. The observations are broadly consistent with predictions of molecular dynamics simulations [Mason, P. E.; et al. J. Phys. Chem. B2009, 113, 3227-3234], indicating that the effects of complex ions on proteins are increasingly predictable in terms of ion hydration, complementary interactions with specific protein groups, and ion-pairing contributions.
用圆二色性光谱法测量了四丙基铵（TPA(+)) 和胍（Gdm(+)) 的氯盐和硫酸盐对色氨酸拉链（trpzip）和α-螺旋（alahel）肽构象稳定性的影响。与 Gdm(+)) 一样，TPA(+) 与平面色氨酸吲哚基团相互作用，扰乱了 trpzip 肽的构象稳定性。硫酸盐对 TPA(+) 影响的影响不大，这表明在高浓度的 Gdm(2)SO(4) 溶液中观察到的杂离子配对不存在。TPA(+)稳定 alahel 肽中的螺旋构象，表明其被排除在肽键之外。这些观察结果与分子动力学模拟的预测大致一致[Mason, P. E.; 等人。J. Phys. Chem. B2009, 113, 3227-3234]，表明复杂离子对蛋白质的影响越来越可以根据离子水合、与特定蛋白质基团的互补相互作用和离子对贡献来预测。
