Blanco F J, Serrano L
European Molecular Biology Laboratory, Heidelberg, Germany.
Eur J Biochem. 1995 Jun 1;230(2):634-49. doi: 10.1111/j.1432-1033.1995.tb20605.x.
The solution structure of the isolated fragments 1-20 (beta-hairpin), 21-40 (alpha-helix) and 41-56 (beta-hairpin), corresponding to all the secondary structure elements of the protein G B1 domain, have been studied by circular dichroism and nuclear magnetic resonance techniques. In the protein G B1-(1-20) fragment turn-like folded structures were detected in water though low populated. In the presence of 30% aqueous trifluoroethanol there is a complex conformational behaviour in which a helical structure at the N-terminal half is formed in equilibrium with random and native-like beta-hairpin structures. The peptide corresponding to the alpha-helix is predominantly unstructured in water, while in 30% trifluoroethanol it highly populates a native alpha-helical conformation, including a (i,i + 5) interaction between hydrophobic residues at its C-terminus. The third peptide was previously reported to form a monomeric native beta-hairpin structure in water [Blanco, F. J., Rivas, G. & Serrano, L. (1994a) Nature Struc. Biol. 1, 584-590]. We show in this work that the beta-hairpin structure is further stabilized in 30% trifluoroethanol and destabilised in the presence of 6 M urea, though some folded structure persists even in these highly denaturing conditions. The conformational properties of these peptides suggests that the second beta-hairpin could be an important folding initiation site on which the rest of the chain folds. Reconstitution experiments failed to show evidence of interaction between the peptides. Algorithms designed to predict the helical and extended conformations of peptides in aqueous solution successfully describe the complicated behaviour of these peptides. Comparison of the predicted and the experimental results with those for a structurally related protein, ubiquitin, shows very strong similarities, the main difference being the switch of the most stable beta-hairpin from the N-terminus in ubiquitin to the C-terminus in protein G.
已通过圆二色性和核磁共振技术研究了与蛋白G B1结构域所有二级结构元件相对应的分离片段1 - 20（β-发夹）、21 - 40（α-螺旋）和41 - 56（β-发夹）的溶液结构。在蛋白G B1 - (1 - 20)片段中，虽然在水中检测到的类似转角的折叠结构数量较少。在30%的三氟乙醇水溶液存在下，存在复杂的构象行为，其中N端一半形成螺旋结构，与随机和天然样β-发夹结构处于平衡状态。对应于α-螺旋的肽在水中主要是无结构的，而在30%的三氟乙醇中，它高度呈现天然α-螺旋构象，包括其C端疏水残基之间的（i，i + 5）相互作用。先前报道第三个肽在水中形成单体天然β-发夹结构[布兰科，F. J.，里瓦斯，G. & 塞拉诺，L.（1994a）《自然结构生物学》1，584 - 590]。我们在这项工作中表明，β-发夹结构在30%的三氟乙醇中进一步稳定，在6 M尿素存在下不稳定，尽管即使在这些高度变性的条件下仍存在一些折叠结构。这些肽的构象性质表明，第二个β-发夹可能是链的其余部分折叠所依赖的重要折叠起始位点。重组实验未能显示肽之间相互作用的证据。设计用于预测水溶液中肽的螺旋和伸展构象的算法成功地描述了这些肽的复杂行为。将预测结果和实验结果与结构相关蛋白泛素的结果进行比较，显示出非常强的相似性，主要区别在于最稳定的β-发夹从泛素的N端切换到蛋白G的C端。
