Park S H, Shalongo W, Stellwagen E
Department of Biochemistry, University of Iowa, Iowa City 52242, USA.
Proteins. 1998 Nov 1;33(2):167-76. doi: 10.1002/(sici)1097-0134(19981101)33:2<167::aid-prot3>3.0.co;2-g.
The model peptide XAAAAEAAARAAAARamide is used to examine the contributions of an N-terminal capping interaction to the conformation and stability of a helical ensemble. The reference peptide has an alanine residue at position X while the capping peptide has a serine residue at this position. The helical ensemble was characterized using circular dichroism measurements and carbonyl-carbon chemical shift measurements of selectively enriched residues. The distribution of helicity within the ensemble of the reference peptide at pH 11 and 0 degrees C appears symmetrical, having a uniform central helix and frayed ends. This distribution is truncated at pH 6 by the repulsive electrostatic interaction between the positively charged alpha-amino group and the positively charged end of the helical macrodipole. The capping peptide forms a side-chain/ main-chain hydrogen bond involving the serine residue and amide of alanine 4. The presence of this hydrogen bond generates a unique motif in the chemical shift profile of its helical ensemble. The conformational stabilization contributed by this hydrogen bond, although cooperatively distributed throughout the helical ensemble, is preferentially focused within the first helical turn. The stabilization provided by this hydrogen bond is able to offset the truncation of the helical ensemble generated by the repulsive electrostatic interaction observed at pH 6.
模型肽XAAAAEAAARAAAARamide用于研究N端封端相互作用对螺旋体构象和稳定性的贡献。参考肽在X位置有一个丙氨酸残基，而封端肽在该位置有一个丝氨酸残基。使用圆二色性测量和选择性富集残基的羰基碳化学位移测量对螺旋体进行表征。参考肽在pH 11和0℃时螺旋体中的螺旋度分布似乎是对称的，具有均匀的中心螺旋和松散的末端。在pH 6时，由于带正电荷的α-氨基与螺旋大偶极带正电荷的末端之间的排斥性静电相互作用，这种分布被截断。封端肽形成了一个涉及丝氨酸残基和丙氨酸4的酰胺的侧链/主链氢键。这种氢键的存在在其螺旋体的化学位移谱中产生了一个独特的基序。尽管这种氢键对构象的稳定作用协同分布在整个螺旋体中，但优先集中在第一个螺旋圈中。这种氢键提供的稳定性能够抵消在pH 6时观察到的由排斥性静电相互作用产生的螺旋体截断。
