期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2003
卷号：100
期号：24
页码：13946-13951
DOI：10.1073/pnas.2336106100
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The design of the synthetic 19-residue peptide Boc-Leu-Aib-Val-Ala-Leu5-Aib-Val-D-Ala-D-Leu-Leu10-Val-Phe-Val-Aib-D-Val15-Leu-Phe-Val-Val-OMe (Aib, -aminoisobutyric acid; OMe, methyl ester) was intended to produce a crystalline peptide with independent helical and hairpin domains. The design was partially based on an octapeptide with the same sequence as residues 11-18 above, which was shown to fold into a {beta}-hairpin in the crystal. However, the crystal structure of the present peptide provided a surprising result. The conformation is the longest characterized right-handed -helix, with as many as three internal D residues in the sequence. The completely helical structure was also unexpected, because {beta}-branched residues such as Val have a low propensity for helix formation in proteins. The helical peptides in the present structure assemble to form hydrophobic channels that accommodate five toluene molecules per peptide along the length of the channel. The structural results illustrate the similarity in energetics between helical and {beta}-hairpin conformations for peptides containing Aib residues. The crystallographic parameters for C107H179N19O22{middle dot}3H2O{middle dot}2.5 toluenes are: space group C2, a = 34.679(3) A, b = 12.866(1) A, c = 31.915(3) A, {beta} = 96.511(8){degrees
