Salt effects on hydrophobic interaction and charge screening in the folding of a negatively charged peptide to a coiled coil (leucine zipper)
Salt effects on hydrophobic interaction and charge screening in the folding of a negatively charged peptide to a coiled coil (leucine zipper)
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DOI：
10.1021/bi972977v
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发表时间：
1998-05-19
期刊：
影响因子：
2.9
通讯作者：
Bosshard, HR
中科院分区：
文献类型：
--
作者：
Jelesarov, I;Dürr, E;Bosshard, HR
卷曲线圈或亮氨酸拉链的稳定性由组成螺旋之间的疏水相互作用和静电力控制。我们设计了一种 30 个残基的肽，具有卷曲螺旋 (abcdefg)(n) 的重复七残基模式，并且每个七肽的 e 和 g 位上有 Glu。由于螺旋二聚体界面以及各个螺旋内的静电排斥，谷氨酸侧链在 pH 值高于 6 时可防止折叠。羧酸盐的质子化将构象从无规卷曲单体改变为卷曲卷曲二聚体。添加盐可促进肽净电荷为-7e 的碱性pH 下的折叠。电荷屏蔽阳离子的性质不如阴离子的性质重要。诱导折叠所需的高盐浓度（>1 M）表明盐诱导的折叠是由蛋白质-水相互作用的改变引起的。亲液阴离子硫酸盐和氟化物促进了折叠，弱亲液剂甲酸在较小程度上促进了折叠，而氯化物和强离液剂高氯酸盐则无效。亲液剂被排除在优先水合的蛋白质表面之外，这通过加强卷曲线圈界面处的疏水相互作用来促进折叠。尽管电荷中和也有助于折叠，但只有当屏蔽阳离子与良好的亲液阴离子配合时才有效。折叠符合从无规卷曲单体到卷曲卷曲二聚体的双态转变，并且是焓驱动的，其特征在于展开热容的变化为3.9 +/- 1.2 kJ mol(-1) K-1。通过荧光停流测量来分析折叠速率。折叠发生在双相反应中，其中快速形成初始二聚体 (k(f) = 2 x 10(7) M-1 s(-1))，随后以同样快速的浓度无关重排形成折叠二聚体 (k > 100 s(-1))。
The stability of a coiled coil or leucine zipper is controlled by hydrophobic interactions and electrostatic forces between the constituent helices. We have designed a 30-residue peptide with the repeating seven-residue pattern of a coiled coil, (abcdefg)(n), and with Glu in positions e and g of each heptad. The glutamate side chains prevented folding at pH values above 6 because of electrostatic repulsion across the helix dimer interface as well as within the individual helices. Protonation of the carboxylates changed the conformation from a random coil monomer to a coiled coil dimer. Folding at alkaline pH where the peptide had a net charge of -7e was promoted by the addition of salts. The nature of the charge screening cation was less important than that of the anion. The high salt concentrations (>1 M) necessary to induce folding indicated that the salt-induced folding resulted from alterations in the protein-water interaction. Folding was promoted by the kosmotropic anions sulfate and fluoride and to a lesser extent by the weak kosmotrope formate, whereas chloride and the strong chaotrope perchlorate were ineffective. Kosmotropes are excluded from the protein surface, which is preferentially hydrated, and this promotes folding by strengthening hydrophobic interactions at the coiled coil interface. Although charge neutralization also contributed to folding, it was effective only when the screening cation was partnered by a good kosmotropic anion. Folding conformed to a two-state transition from random coil monomer to coiled coil dimer and was enthalpy driven and characterized by a change in the heat capacity of unfolding of 3.9 +/- 1.2 kJ mol(-1) K-1. The rate of folding was analyzed by fluorescence stopped-flow measurements. Folding occurred in a biphasic reaction in which the rapid formation of an initial dimer (k(f) = 2 x 10(7) M-1 s(-1)) was followed by an equally rapid concentration-independent rearrangement to the folded dimer (k > 100 s(-1)).