Dyson H J, Sayre J R, Merutka G, Shin H C, Lerner R A, Wright P E
Department of Molecular Biology, Scripps Research Institute, La Jolla, CA 92037.
J Mol Biol. 1992 Aug 5;226(3):819-35. doi: 10.1016/0022-2836(92)90634-v.
In an attempt to understand the earliest events in the protein folding pathway, the complete sequence of French bean plastocyanin has been synthesized as a series of short peptide fragments, and the conformational preferences of each peptide examined in aqueous solution using proton n.m.r. methods. Plastocyanin consists largely of beta-sheet, with reverse turns and loops between the strands of the sheet, and one short helix. The n.m.r. experiments indicate that most of the peptides derived from the plastocyanin sequence have remarkably little propensity to adopt folded conformations in aqueous solution, in marked contrast to the peptides derived from the helical protein, myohemerythrin (accompanying paper). For most plastocyanin peptides, the backbone dihedral angles are predominantly in the beta-region of conformational space. Some of the peptides show weak NOE connectivities between adjacent amide protons, indicative of small local populations of backbone conformations in the a region of (phi,psi) space. A conformational preference for a reverse turn is seen in the sequence Ala65-Pro-Gly-Glu68, where a turn structure is found in the folded protein. Significantly, the peptide sequences that populate the alpha-region of (phi,psi) space are mostly derived from turn and loop regions in the protein. The addition of trifluoroethanol does not drive the peptides into helical conformations. In one region of the sequence, the n.m.r. spectra provide evidence of the formation of a hydrophobic cluster involving aromatic and aliphatic side-chains. These results have significance for understanding the initiation of protein folding. From these studies of the fragments of plastocyanin (this paper) and myohemerythrin (accompanying paper), it appears that there is a pre-partitioning of the conformational space sampled by the polypeptide backbone that is related to the secondary structure in the final folded state.
为了了解蛋白质折叠途径中最早发生的事件，菜豆质体蓝素的完整序列已被合成为一系列短肽片段，并使用质子核磁共振方法在水溶液中检测了每个肽的构象偏好。质体蓝素主要由β-折叠组成，在折叠链之间有反向转角和环，还有一个短螺旋。核磁共振实验表明，与来自螺旋蛋白肌红蛋白（附文）的肽相比，源自质体蓝素序列的大多数肽在水溶液中形成折叠构象的倾向非常小。对于大多数质体蓝素肽，主链二面角主要处于构象空间的β区域。一些肽在相邻酰胺质子之间显示出较弱的核Overhauser效应（NOE）连接性，这表明在（φ，ψ）空间的α区域中存在少量局部主链构象。在序列Ala65-Pro-Gly-Glu68中观察到对反向转角的构象偏好，在折叠蛋白中发现了转角结构。值得注意的是，占据（φ，ψ）空间α区域的肽序列大多源自蛋白质中的转角和环区域。添加三氟乙醇并不会促使肽形成螺旋构象。在序列的一个区域，核磁共振光谱提供了涉及芳香族和脂肪族侧链的疏水簇形成的证据。这些结果对于理解蛋白质折叠的起始具有重要意义。从对质体蓝素片段（本文）和肌红蛋白（附文）的这些研究来看，似乎多肽主链所采样的构象空间存在一种预划分，这与最终折叠状态下的二级结构有关。
