Pavone V, Lombardi A, Saviano M, Di Blasio B, Nastri F, Fattorusso R, Maglio O, Isernia C
Centro Interdipartimentale di Ricerca su Peptidi Bioattivi and CEINGE-Biotecnologie Avanzate, University of Naples, Federico II, Italy.
Biopolymers. 1994 Nov;34(11):1505-15. doi: 10.1002/bip.360341108.
In the present paper we describe the synthesis, purification, single crystal x-ray analysis, and solution structural characterization by nmr spectroscopy, combined with restrained molecular dynamic simulations, of the cyclic hexapeptide cyclo-(Pro-Phe-beta-Ala-Phe-Phe-beta-Ala). The peptide was synthesized by classical solution methods and the cyclization of the free hexapeptide was accomplished in good yields in diluted methylenechloride solution using N,N-dicyclohexyl-carbodiimide. The compound crystallizes in the monoclinic space group P2(1) from methanol/ethyl acetate. The molecule adopts in the solid state a conformation characterized by cis beta-Ala6-Pro1 peptide bond. The alpha-amino acid residues are at the corner positions of turned structures. The Pro1-Phe2 segment is incorporated in a pseudo type I beta-turn, while Phe4-Phe5 is in a typical type I beta-turn. Assignment of all 1H and 13C resonances was achieved by homo- and heteronuclear two-dimensional techniques in dimethylsulfoxide (DMSO) solutions. The conformational analysis was based on interproton distances derived from rotating frame nuclear Overhauser effect spectroscopy spectra and homonuclear coupling constants. Restrained molecular dynamic simulation in vacuo was also performed to built refined molecular models. The molecule is present in DMSO solution as two slowly interconverting conformers, characterized by a cis-trans isomerism around the beta-Ala6-Pro1 peptide bond. This work confirms our expectations on the low propensity of beta-alanyl residues to be positioned at the corners of turned structure.
在本文中，我们描述了环六肽环-（脯氨酸-苯丙氨酸-β-丙氨酸-苯丙氨酸-苯丙氨酸-β-丙氨酸）的合成、纯化、单晶X射线分析以及通过核磁共振光谱结合受限分子动力学模拟进行的溶液结构表征。该肽通过经典溶液法合成，游离六肽的环化在稀释的二氯甲烷溶液中使用N，N-二环己基碳二亚胺以良好的产率完成。该化合物从甲醇/乙酸乙酯中结晶出单斜空间群P2(1)。该分子在固态中采用以顺式β-丙氨酸6-脯氨酸1肽键为特征的构象。α-氨基酸残基位于转折结构的拐角位置。脯氨酸1-苯丙氨酸2片段包含在一个假I型β-转角中，而苯丙氨酸4-苯丙氨酸5处于典型的I型β-转角中。通过在二甲亚砜（DMSO）溶液中的同核和异核二维技术实现了所有1H和13C共振的归属。构象分析基于从旋转框架核Overhauser效应光谱和同核耦合常数得出的质子间距离。还进行了真空受限分子动力学模拟以构建精细的分子模型。该分子在DMSO溶液中以两种缓慢相互转化的构象存在，其特征是围绕β-丙氨酸6-脯氨酸1肽键的顺反异构。这项工作证实了我们对β-丙氨酰残基位于转折结构拐角处的低倾向的预期。
