The preferred conformation of the tripeptide Ala-Phe-Ala in water is an inverse gamma-turn: implications for protein folding and drug design.
The preferred conformation of the tripeptide Ala-Phe-Ala in water is an inverse gamma-turn: implications for protein folding and drug design.
复制标题
三肽 Ala-Phe-Ala 在水中的首选构象是逆伽马转角：对蛋白质折叠和药物设计的影响。
作者：
A. Motta;M. Reches;Lucia Pappalardo;G. Andreotti;E. Gazit
最近的研究提供了证据表明，与三肽一样短的多肽确实采用了首选构象。在此，我们报道了三肽Ala-Phe-Ala(AFA)在水溶液中优先形成逆伽马转角。圆二色谱(CD)表明存在一个主要的转角结构，傅里叶变换红外光谱(FTIR)表明存在一个伽马转角，与溶剂分子形成一个分叉的氢键。高分辨结构是通过核磁共振波谱和计算相结合得到的。基于30个明确的ROESY推导的距离约束(包括Ala(1)和Ala(3)之间的Halpha-NHNOE和Ala(1)的CO基团和Ala(3)的NH基团之间的氢键)，计算清楚地证明了以Phe(2)为中心的逆伽马转角的存在。根据NOE数据，我们估计伽马转角的摩尔分数为0.65。因为对于AFA，还报告了延伸的β-链[Eker，F.，Griebenow，K.，CaO，X.，Nafie，L.A.，和Schweitzer-Stenner，R.(2004)Proc.娜塔莉。阿卡德。SCI。U.S.A.101,10054-10059]，我们研究了伽马转角和β-链可能代表两种主要构象的可能性。通过使用最佳拟合方法计算实验NOE作为两种结构影响的加权平均值，我们能够很好地根据两个极限构象计算280K的主链NOE，得到伽马转角构象和β链构象的摩尔分数分别为0.60和0.40，与NOE数据一致。在蛋白质折叠事件的成核和小肽和模拟多肽药物的设计的背景下，讨论了小结构元件存在优选构象的含义。
Recent studies have provided evidence that peptides as short as tripeptides do adopt preferred conformations. Here we report that the tripeptide Ala-Phe-Ala (AFA) in aqueous solution preferentially forms an inverse gamma-turn. Circular dichroism (CD) indicated the presence of a predominant turn structure, and Fourier transform infrared (FTIR) bands suggested the presence of a gamma-turn forming a bifurcated H-bond with the solvent molecules. The high-resolution structure was obtained by a combined use of NMR spectroscopy and calculations. On the basis of 30 unambiguous ROESY-derived distance restraints (including the Halpha-NH NOE between Ala(1) and Ala(3) and a hydrogen bond between the CO group of Ala(1) and the NH group of Ala(3)), calculations clearly demonstrated the presence of an inverse gamma-turn centered on Phe(2). From NOE data, we estimated a mole fraction for the gamma-turn of 0.65. Since for AFA an extended beta-strand was also reported [Eker, F., Griebenow, K., Cao, X., Nafie, L. A., and Schweitzer-Stenner, R. (2004) Proc. Natl. Acad. Sci. U.S.A. 101, 10054-10059], we investigated the possibility that gamma-turn and beta-strand may represent two major conformations. By using a best-fit procedure that calculated experimental NOEs as weighted averages of the effects originating from both structures, we were able to calculate with good accuracy the backbone NOEs at 280 K in terms of the two limiting conformers, yielding a mole fraction for the gamma-turn and beta-strand conformations of 0.60 and 0.40, respectively, in good agreement with those found by NOE data. The implication of the existence of a preferred conformation by a small structural element is discussed in the context of the nucleation of protein folding events and the design of small peptide and peptidomimetic drugs.