β-Hairpins Generated from Hybrid Peptide Sequences Containing both α- and β-Amino Acids

✍ Scribed by Hosahudya N. Gopi; Rituparna S. Roy; Srinivasa R. Raghothama; Isabella L. Karle; Padmanabhan Balaram

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: German
• Weight: 342 KB
• Volume: 85
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/1522-2675(200210)85:10<3313::aid-hlca3313>3.0.co;2-p

✦ Synopsis

The incorporation of the b-amino acid residues into specific positions in the strands and b-turn segments of peptide hairpins is being systematically explored. The presence of an additional torsion variable about the C(a)ÀC(b) bond (q) enhances the conformational repertoire in b-residues. The conformational analysis of three designed peptide hairpins composed of a/b-hybrid segments is described: ), and Boc-Leu-Val-bPhe-Val-D Pro-Gly-Leu-bPhe-Val-Val-OMe (3). 500-MHz 1 H-NMR Analysis supports a preponderance of b-hairpin conformation in solution for all three peptides, with critical cross-strand NOEs providing evidence for the proposed structures. The crystal structure of peptide 2 reveals a b-hairpin conformation with two b-residues occupying facing, non-H-bonded positions in antiparallel b-strands. Notably, bVal(3) adopts a gauche conformation about the C(a)ÀC(b) bond (q 658) without disturbing cross-strand H-bonding. The crystal structure of 2, together with previously published crystal structures of peptides 3 and Boc-bPhe-bPhe-D Pro-Gly-bPhe-bPhe-OMe, provide an opportunity to visualize the packing of peptide sheets with local -polar segments× formed as a consequence of reversal peptide-bond orientation. The available structural evidence for hairpins suggests that b-residues can be accommodated into nucleating turn segments and into both the H-bonding and non-H-bonding positions on the strands.