Stellwagen E, Shalongo W
Department of Biochemistry, University of Iowa, Iowa City 52242, USA.
Biopolymers. 1997;43(6):413-8. doi: 10.1002/(SICI)1097-0282(1997)43:6<413::AID-BIP3>3.0.CO;2-Y.
The thermal dependence of the carbonyl carbon chemical shift of each residue in a helical peptide may be analyzed in terms of a two-state helix/coil transition. Such analyses generate values for the chemical shift of each residue in the helical and in the coil conformational ensembles of the peptide. The sequence dependence of the difference in these two values, termed the difference chemical shift, provides a description of the mean distribution of helicity within the helical ensemble. In this report, we improve two aspects of the procedures used to analyze prior chemical shift measurements of the helical peptide acetylW (EAAAR)3Aamide. The new difference chemical shift values for 16 of the 18 residues describe a very uniform central helical ensemble with frayed ends. However, the difference chemical shift values for the two remaining residues, alanines 03 and 08, are significantly diminished relative to this uniform distribution. Each of these two alanine residues is located i-4 to a glutamate residue. It is suggested that the difference chemical shifts for these two alanine residues are diminished by a self-capping interaction within the i + 4 glutamate residues.
螺旋肽中每个残基的羰基碳化学位移的热依赖性可以根据两态螺旋/无规卷曲转变进行分析。此类分析可得出肽在螺旋构象集合体和无规卷曲构象集合体中每个残基的化学位移值。这两个值的差值，即所谓的差值化学位移，其序列依赖性描述了螺旋集合体内螺旋度的平均分布。在本报告中，我们改进了用于分析先前对螺旋肽乙酰W（EAAAR）3A酰胺进行的化学位移测量的方法的两个方面。18个残基中有16个残基的新差值化学位移值描述了一个非常均匀的中央螺旋集合体，其末端存在松散现象。然而，其余两个残基（丙氨酸03和08）的差值化学位移值相对于这种均匀分布明显减小。这两个丙氨酸残基中的每一个都位于谷氨酸残基的i-4位置。有人认为，这两个丙氨酸残基的差值化学位移因i + 4谷氨酸残基内的自封端相互作用而减小。
