Dyson H J, Rance M, Houghten R A, Wright P E, Lerner R A
Department of Molecular Biology, Research Institute of Scripps Clinic, La Jolla, CA 92037.
J Mol Biol. 1988 May 5;201(1):201-17. doi: 10.1016/0022-2836(88)90447-0.
1H nuclear magnetic resonance experiments indicate formation of secondary structures in water solutions of a synthetic immunogenic peptide of sequence EVVPHKKMHKDFLEKIGGL corresponding to the C-helix (residues 69 to 87) of myohemerythrin. The conformational ensemble consists of a set of turn-like structures, distributed over the C-terminal half of the peptide and rapidly interconverting by way of unfolded states. These structures, termed nascent helix, are stabilized into helical structure with long-range order in water/trifluorethanol mixtures. Circular dichroism measurements confirm the presence of 50% helix in water/trifluoroethanol but show no evidence of helicity in water solutions of the peptide. It is apparent that no one member of the transient set of helical conformations which constitutes the nascent helix is sufficiently long to be detectable by circular dichroism experiments. No preferred conformations could be detected by nuclear magnetic resonance in the N-terminal half of the peptide, either in water or water/trifluoroethanol mixtures. This region of the peptide is stabilized in helix by long-range interactions in the folded protein. The possible role of nascent secondary structure in induction of antipeptide antibodies and in initiation of protein folding is discussed.
1H核磁共振实验表明，对应于肌红蛋白C螺旋（第69至87位残基）的序列为EVVPHKKMHKDFLEKIGGL的合成免疫原性肽在水溶液中形成二级结构。构象集合由一组类似转角的结构组成，分布在肽的C端一半，并通过未折叠状态快速相互转换。这些结构被称为新生螺旋，在水/三氟乙醇混合物中稳定为具有长程有序的螺旋结构。圆二色性测量证实了在水/三氟乙醇中存在50%的螺旋，但在肽的水溶液中没有显示出螺旋性的证据。显然，构成新生螺旋的瞬态螺旋构象集合中没有一个成员足够长，能够通过圆二色性实验检测到。无论是在水中还是在水/三氟乙醇混合物中，通过核磁共振在肽的N端一半都检测不到优选构象。肽的这一区域通过折叠蛋白中的长程相互作用稳定为螺旋。讨论了新生二级结构在诱导抗肽抗体和启动蛋白质折叠中的可能作用。
