Monera O D, Zhou N E, Kay C M, Hodges R S
Department of Biochemistry, University of Alberta, Edmonton, Canada.
J Biol Chem. 1993 Sep 15;268(26):19218-27.
An antiparallel coiled-coil has been designed and characterized as a model for studying protein folding and assembly. This heterostranded antiparallel coiled-coil was formed by an interchain disulfide bond between cysteine residues at position 2 of one chain and at position 33 of the other chain. Each peptide chain has 35 residues which are composed of five heptad repeats of the sequence K-L-E-A-L-E-G with a single Leu-->Ala substitution at position 16. Two homostranded parallel coiled-coils were also formed as co-products of the oxidation reaction to form the interchain disulfide bond. The CD spectra of the parallel and antiparallel peptides were very similar and their high molar ellipticities at 220 nm did not increase in the presence of 50% trifluoroethanol. These data suggest that, like the parallel peptides, the antiparallel peptide also exists in a coiled-coil structure. Urea and guanidine hydrochloride denaturation studies, in conjunction with molecular modeling studies, suggest that there are no physical restrictions to the packing of hydrophobic residues in an antiparallel coiled-coil. However, interchain electrostatic interactions can have positive or negative contributions to the overall stability of the disulfide-bridged coiled-coil. In addition, interchain electrostatic interactions appear to play a major role in protein folding by controlling the parallel or antiparallel alignment of the alpha-helical polypeptide chains. This study is also for the first time providing us with a new understanding of the information that can be obtained from urea and guanidine hydrochloride denaturation studies of proteins concerning the contributions of hydrophobic and electrostatic interactions on stability.
一种反平行卷曲螺旋已被设计并表征为研究蛋白质折叠和组装的模型。这种异链反平行卷曲螺旋是由一条链第2位的半胱氨酸残基与另一条链第33位的半胱氨酸残基之间的链间二硫键形成的。每条肽链有35个残基，由序列K-L-E-A-L-E-G的五个七肽重复序列组成，在第16位有一个Leu→Ala的单取代。氧化反应形成链间二硫键时，还同时生成了两种同链平行卷曲螺旋作为副产物。平行和反平行肽的圆二色光谱非常相似，并且在50%三氟乙醇存在下，它们在220 nm处的高摩尔椭圆率并未增加。这些数据表明，与平行肽一样，反平行肽也以卷曲螺旋结构存在。尿素和盐酸胍变性研究结合分子模拟研究表明，反平行卷曲螺旋中疏水残基的堆积没有物理限制。然而，链间静电相互作用对二硫键连接的卷曲螺旋的整体稳定性可能有正向或负向贡献。此外，链间静电相互作用似乎在蛋白质折叠中通过控制α-螺旋多肽链的平行或反平行排列起主要作用。这项研究还首次让我们对从蛋白质的尿素和盐酸胍变性研究中获得的有关疏水和静电相互作用对稳定性贡献的信息有了新的认识。
