Peptide backbone folding induced by the C<sup>α</sup>-tetrasubstituted cyclic α-amino acids 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) and 1-aminocyclopentane-1-carboxylic acid (Ac<sub>5</sub>c). A joint computational and experimental study
作者:Massimiliano Aschi、Gino Lucente、Fernando Mazza、Adriano Mollica、Enrico Morera、Marianna Nalli、Mario Paglialunga Paradisi
DOI:10.1039/b212247b
日期:——
The conformational study of a new group of synthetic peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt), a cysteine-related achiral residue, has been carried out through a joint application of computational and experimental methodologies. Molecular Dynamics simulations clearly suggest the tendency of this molecule to adopt a γ-turn conformation in vacuum and help in analyzing the complex and crucial conformational behaviour of the dithiolane ring which appears to preferentially adopt a Cs-like structure. Electronic structure calculations carried out in solution using the Density Functional Theory also indicate the preservation of the γ-like folding in apolar solvents and the helix-like one in more polar solvents. A comparison with the achiral 1-aminocycloalkane-1-carboxylic acid (Ac5c) has been carried out using the same computational tools. NMR and IR data on dipeptide derivatives containing the Adt or Ac5c residue show that in chloroform solution all the models prefer a γ-turn structure, centered at the cyclic residue, stabilized by an intramolecular H-bond, whereas in a more polar solvent, i.e. dimethyl sulfoxide, this folding is not maintained. The experimental conformational studies, extended to N-Boc protected tripeptides, clearly indicate the remarkable tendency of both the five-membered Cα-tetrasubstituted cyclic amino acids Adt and Ac5c to induce the γ-turn structure also in models able to adopt the β-bend conformation.
对含有4-氨基-1,2-二硫杂环戊烷-4-羧酸(Adt)这一与半胱氨酸相关的无喹啉残基的新型合成肽群体的构象研究,通过计算方法与实验方法的联合应用得以进行。分子动力学模拟清楚地表明该分子在真空中倾向于采用γ-转构象,并有助于分析二硫杂环的复杂而关键的构象行为,该环似乎更倾向于采用Cs类似的结构。使用密度泛函理论在溶液中进行的电子结构计算同样表明,在非极性溶剂中形成的γ-like折叠保持,而在更极性的溶剂中则表现出螺旋状结构。使用相同的计算工具与无喹啉的1-氨基环烷基-1-羧酸(Ac5c)进行了比较。含有Adt或Ac5c残基的二肽衍生物在氯仿溶液中的NMR和IR数据表明,所有模型都更倾向于在环状残基中心形成由分子内氢键稳定的γ-转构象,而在更极性的溶剂(如二甲基亚砜)中这一折叠并未维持。扩展到N-Boc保护的三肽的实验构象研究清楚地显示,五元Cα-四取代环氨基酸Adt和Ac5c都显著倾向于在能够采用β-弯曲构象的模型中诱导γ-转构象。