Cold denaturation of monomeric peptide helices
Cold denaturation of monomeric peptide helices
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DOI：
10.1021/ja961143h
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发表时间：
1996-10-23
影响因子：
15
通讯作者：
Tong, H
中科院分区：
文献类型：
--
作者：
Andersen, NH;Cort, JR;Tong, H
从热力学的角度来看，球状蛋白质的稳定构象代表了非常大的相反熵和焓项之间的微妙妥协，疏水效应起着重要作用。1冷变性研究，通常通过加入有限数量的变性剂2或在非最佳pH 3下进行，以减少折叠状态的热变性优势，在阐明蛋白质折叠的热力学方面具有关键作用。当未折叠状态具有较大的热容时，任何宏观双态解折叠都预期会发生冷变性;脂肪残基显著掩埋的蛋白质通常显示60-70（JK-1）/残基（res）的ΔCp值。已观察到熔融球状态的蛋白质4和螺旋肽寡聚体5的冷变性;然而，从未观察到单体螺旋肽的冷变性。6肽螺旋在量热法和圆二色性（CD）法中显示出非常宽的熔融转变，这排除了ΔCp的直接测量。[9]富含丙氨酸的螺旋去折叠的ΔCp的计算范围为-27至+8.3（JK-1）/res（基于非极性与极性表面积的估计变化）。[10]从肽螺旋的实验数据得出的最大ΔCp为+ 19（JK-1）/res 6c。我们现在报告，戏剧性的冷变性可以观察到在六氟异丙醇水溶液（HFIP）的两亲性螺旋和富含丙氨酸的螺旋与零疏水矩。该现象用针对此处所示的四种肽收集的数据来说明（在富含氟代醇的介质中螺旋的程度由下划线指示）。
From the perspective of thermodynamics, the stable conformation of globular proteins represents a delicate compromise between very large opposing entropy and enthalpy terms with the hydrophobic effect playing a significant role. 1 Cold denaturation studies, typically carried out with the addition of limited quantities of denaturants2 or at nonoptimal pH3 to reduce the enthalpic advantage of the folded state, have had a pivotal role in elucidating the thermodynamics of protein folding. Cold denaturation is expected for any macroscopic two-state unfolding when the unfolded state has a larger heat capacity; proteins with significant burial of fatty residues typically display ΔCp values of 60-70 (JK-1)/residue (res). Cold denaturation has been observed for molten globule states of proteins4 and for helical peptide oligomers; 5 however, it has never been observed for a monomeric helical peptide. 6 Peptide helices display very broad melting transitions both calorimetrically and by circular dichroism (CD) and this precludes a direct measurement of ΔCp. 9 Calculations of the ΔCp expected for the unfolding of an alanine-rich helix range from-27 to+ 8.3 (JK-1)/res (based on the estimated changes in apolar versus polar surface area). 10 The largest ΔCp derived from experimental data for a peptide helix is+ 19 (JK-1)/res6c. We now report that dramatic cold denaturation can be observed in aqueous hexafluoroisopropanol (HFIP) for both amphiphilic helices and alanine-rich helices with zero hydrophobic moment. The phenomenon is illustrated with data collected for the four peptides shown here (the extent the helix in fluoroalcohol-rich media is indicated by underlining).