Equilibrium unfolding of the poly(glutamic acid)20 helix
Equilibrium unfolding of the poly(glutamic acid)20 helix
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DOI：
10.1002/bip.20719
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发表时间：
2007-06-15
期刊：
影响因子：
2.9
通讯作者：
Winkler, Jay R.
中科院分区：
文献类型：
--
作者：
Finke, John M.;Jennings, Patricia A.;Winkler, Jay R.
用FRET、圆二色性和分子动力学模拟方法研究了20个残基的聚谷氨酸肽（E-20）的平衡结构系综。分别在N-和C-末端引入FRET供体邻氨基苯甲酰胺和受体3-硝基酪氨酸。采用圆二色性、稳态FRET和时间分辨FRET测量来表征不同pH条件下的螺旋部分和末端到末端距离：pH 4（60% α-螺旋）、pH 6（0% α-螺旋）和pH 9（0% α-螺旋）。在pH 4下，在24埃下测量端到端距离，并确定其显著小于对于相同长度的α-螺旋预测的31埃。在pH 6和91下，端到端距离分别测量为> 31和39 A，这两者被确定为显著大于对于相同长度的自由连接的无规卷曲预测的27 A。为了更好地理解这种肽中不寻常的螺旋-卷曲转变背后的物理力，构建了E-20的三种理论MD模型：（1）纯α-螺旋，（2）具有等效吸引性分子内接触的α-螺旋，和（3）具有末端加权分子内接触（“粘性末端”）的弱α-螺旋。使用MD模拟，从模型3计算的弯曲螺旋结构被认为是最接近的协议与实验数据。(C)2007 Wiley Periodicals，Inc. Biopolymers 86：193-211，2007.
The equilibrium structural ensemble of a 20-residue polyglutamic acid peptide (E-20) was studied with FRET, circular dichroism, and molecular dynamics (MD) simulations. A FRET donor, o-aminobenzamide, and acceptor, 3-nitrotyrosine, were introduced at the N- and C-termini, respectively. circular dichroisrn, steady state FRET, and time-resolved FRET measurements were employed to characterize the fraction helix and end-to-end distance under different pH conditions: pH 4 (60% alpha -helix), pH 6 (0% alpha-helix), and pH 9 (0% a -helix). At pH 4, the end-to-end distance was measured at 24 angstrom and determined to be considerably less than the 31 angstrom predicted for an alpha-helix of the same length. At pH 6 and 91 the end-to-end distance was measured at > 31 and 39 A respectively, both which are determined to be considerably greater than the 27 A predicted for a freely jointed random coil of the same length. To better understand the physical forces underlying the unusual helix-coil transition in this peptide, three theoretical MD models of E-20 were constructed: (1) a pure alpha-helix, (2) an alpha-helix with equivalent attractive intramolecular contacts, and (3) a weak alpha-helix with termini-weighted intramolecular contacts ("sticky ends"). Using MD simulations, the bent helix structure calculated from Model 3 was found to be the closest in agreement with the experimental data. (C) 2007 Wiley Periodicals, Inc. Biopolymers 86: 193-211, 2007.