FOLDING OF IMMUNOGENIC PEPTIDE-FRAGMENTS OF PROTEINS IN WATER SOLUTION .1. SEQUENCE REQUIREMENTS FOR THE FORMATION OF A REVERSE TURN
FOLDING OF IMMUNOGENIC PEPTIDE-FRAGMENTS OF PROTEINS IN WATER SOLUTION .1. SEQUENCE REQUIREMENTS FOR THE FORMATION OF A REVERSE TURN
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DOI：
10.1016/0022-2836(88)90446-9
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发表时间：
1988-05-05
影响因子：
5.6
通讯作者：
WRIGHT, PE
中科院分区：
文献类型：
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作者：
DYSON, HJ;RANCE, M;WRIGHT, PE
通过1H核磁共振对β-在水溶液中的几个系列的短线性肽中的含转角构象异构体已经证明了对氨基酸序列的依赖性，这对蛋白质折叠的起始具有重要意义。这些肽由序列Tyr-Pro-Tyr-Asp的许多变体组成，其反式异构体先前显示在水中含有反转。二维双框架核Overhauser效应光谱提供了明确的证据，大量人口的反转构象发生在水溶液中的某些这些肽。在未折叠状态下，肽主要采用延伸链（β）。水中的构象从观察到的核Overhauser效应连接性来看，反式异构体中的反转可能主要是II型。的酰胺质子共振的温度系数低的残基在位置4的转折表明存在的分子内氢键。β的存在-通过圆二色性测量已经证实了某些肽的转角构象。在序列Tyr-Pro-Tyr-Asp-瓦尔中3和4位的取代可以增强或消除β-天冬氨酸的功能。在反式肽异构体中转化群体。转角3位的残基是其稳定性的主要决定因素。少量的额外的稳定化似乎是由于残基4的侧链和未封闭的氨基末端之间的静电相互作用。对于Tyr-Pro-X-Asp-瓦尔系列的肽，其中X代表除Trp和Pro之外的所有L-氨基酸，Asp 4酰胺质子共振的温度系数提供了β-Asp的测量。转人口。β-以这种方式测量的水溶液中的转化数与β-从蛋白质晶体结构确定的转动概率。这表明，通常是局部氨基酸序列，而不是折叠蛋白质中的中程至长程相互作用决定β-在折叠状态下转动构象。这样的序列是蛋白质折叠起始位点的极好候选者。高人口的结构形式似乎是存在于顺式异构体的某些肽，如所示的顺式异构体的比例相当大的增加，并通过测量核Overhauser效应和3 JNa耦合常数。主要结构表现为B型VI β-反过来，顺式脯氨酸在位置3。β的估计值-转角群体表明，在最有利的肽中，多达70%的顺式异构体可能以VI型转角构象存在。反式肽的转角群体较小，但对于某些肽可能高达50%。观察到的β-蛋白质的小肽片段中的转角表明，在折叠条件下，在多肽链中预期转角，其中它们可能对蛋白质折叠途径具有深远的影响。
A systematic examination by 1H nuclear magnetic resonance of the population of .beta.-turn-containing conformers in several series of short linear peptides in water solution has demonstrated a dependence on amino acid sequence which has important implications for initiation of protein folding. The peptides consist of a number of variants of the sequence Tyr-Pro-Tyr-Asp, the trans isomer of which was previously shown to contain a reverse turn in water. Two-dimensional rotating-frame nuclear Overhauser effect spectroscopy provides unequivocal evidence that substantial populations of reverse turn conformations occur in water solutions of certain of these peptides. In the unfolded state, the peptides adopt predominantly extended chain (.beta.) conformations in water. It appears probable from the nuclear Overhauser effect connectivities observed that the reverse turns in the trans isomers are predominantly type II. The low temperature coefficient of the amide proton resonance of the residue at position 4 of the turn suggests the presence of an intramolecular hydrogen bond. The presence of the .beta.-turn conformation has been confirmed for certain peptides by circular dichroism measurements. Substitutions at positions 3 and 4 in the sequence Tyr-Pro-Tyr-Asp-Val can enhance or abolish the .beta.-turn population in the trans peptide isomers. The residue at position 3 of the turn is the primary determinant of its stability. A small amount of additional stabilization appears to result from an electrostatic interaction between the side-chain of residue 4 and the unblocked amino terminus. For peptides of the series Tyr-Pro-X-Asp-Val, where X represents all L-amino acids except Trp and Pro, the temperature coefficient of the Asp4 amide proton resonance provides a measure of the .beta.-turn population. The .beta.-turn populations in water solution measured in this way correlate with the .beta.-turn probabilities determined from protein crystal structures. This indicates that it is frequently the local amino acid sequence, rather than medium- to long-range interactions in the folded protein, that determines the .beta.-turn conformation in the folded state. Such sequences are excellent candidates for protein folding initiation sites. A high population of structured forms appears to be present in the cis isomer of certain of the peptides, as shown by a considerable increase in the proportion of the cis isomer and by measurement of nuclear Overhauser effects and 3JNa coupling constants. The predominant structure appears to b a type VI .beta.-turn, with cis-proline at position 3. Estimates of the .beta.-turn population suggest that, in the most favourable peptides, as much as 70% of the cis isomer may exist in type VI turn conformations. The turn population for the trans peptides is smaller, but may be as high as 50% for certain peptides. The observed stability of .beta.-turns in small peptide fragments of proteins suggests that turns are to be expected in polypeptide chains under folding conditions where they may have a profound influence on protein folding pathways.