Chin Wutharath, Dognon Jean-Pierre, Canuel Clélia, Piuzzi François, Dimicoli Iliana, Mons Michel, Compagnon Isabelle, von Helden Gert, Meijer Gerard
Laboratoire Francis Perrin, Service des Photons, Atomes et Molécules, Centre d'Etudes de Saclay, Bâtiment 522, 91191 Gif-sur-Yvette Cedex, France.
J Chem Phys. 2005 Feb 1;122(5):54317. doi: 10.1063/1.1839862.
The conformational structure of short peptide chains in the gas phase is studied by laser spectroscopy of a series of protected dipeptides, Ac-Xxx-Phe-NH(2), Xxx=Gly, Ala, and Val. The combination of laser desorption with supersonic expansion enables us to vaporize the peptide molecules and cool them internally; IR/UV double resonance spectroscopy in comparison to density functional theory calculations on Ac-Gly-Phe-NH(2) permits us to identify and characterize the conformers populated in the supersonic expansion. Two main conformations, corresponding to secondary structures of proteins, are found to compete in the present experiments. One is composed of a doubly gamma-fold corresponding to the 2(7) ribbon structure. Topologically, this motif is very close to a beta-strand backbone conformation. The second conformation observed is the beta-turn, responsible for the chain reversal in proteins. It is characterized by a relatively weak hydrogen bond linking remote NH and CO groups of the molecule and leading to a ten-membered ring. The present gas phase experiment illustrates the intrinsic folding properties of the peptide chain and the robustness of the beta-turn structure, even in the absence of a solvent. The beta-turn population is found to vary significantly with the residues within the sequence; the Ac-Val-Phe-NH(2) peptide, with its two bulky side chains, exhibits the largest beta-turn population. This suggests that the intrinsic stabilities of the 2(7) ribbon and the beta-turn are very similar and that weakly polar interactions occurring between side chains can be a decisive factor capable of controlling the secondary structure.
通过对一系列保护二肽Ac-Xxx-Phe-NH₂（Xxx = Gly、Ala和Val）进行激光光谱研究，来探究气相中短肽链的构象结构。激光解吸与超声速膨胀相结合，使我们能够使肽分子汽化并在内部冷却它们；与对Ac-Gly-Phe-NH₂进行密度泛函理论计算相比，红外/紫外双共振光谱使我们能够识别和表征超声速膨胀中存在的构象异构体。在当前实验中发现两种主要构象，它们对应于蛋白质的二级结构，相互竞争。一种由对应于2(7)带状结构的双γ折叠组成。从拓扑学上讲，这个基序非常接近β链主链构象。观察到的第二种构象是β转角，它负责蛋白质中的链反转。其特征是分子中远距离的NH和CO基团之间存在相对较弱的氢键，形成一个十元环。当前的气相实验说明了肽链的内在折叠特性以及β转角结构的稳健性，即使在没有溶剂的情况下也是如此。发现β转角的比例会随着序列中的残基而显著变化；具有两个大体积侧链的Ac-Val-Phe-NH₂肽表现出最大的β转角比例。这表明2(7)带状结构和β转角的内在稳定性非常相似，并且侧链之间发生的弱极性相互作用可能是能够控制二级结构的决定性因素。
