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β ‐Hairpins Generated from Hybrid Peptide Sequences Containing both α ‐ and β ‐Amino Acids
Author(s) -
Gopi Hosahudya N.,
Roy Rituparna S.,
Raghothama Srinivasa R.,
Karle Isabella L.,
Balaram Padmanabhan
Publication year - 2002
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(200210)85:10<3313::aid-hlca3313>3.0.co;2-p
Subject(s) - chemistry , antiparallel (mathematics) , peptide , peptide bond , crystallography , peptide conformation , stereochemistry , amino acid , crystal structure , dipeptide , peptide sequence , hydrogen bond , molecule , biochemistry , physics , organic chemistry , quantum mechanics , magnetic field , gene
The incorporation of the β ‐amino acid residues into specific positions in the strands and β ‐turn segments of peptide hairpins is being systematically explored. The presence of an additional torsion variable about the C( α )C( β ) bond ( θ ) enhances the conformational repertoire in β ‐residues. The conformational analysis of three designed peptide hairpins composed of α / β ‐hybrid segments is described: Boc‐Leu‐Val‐Val‐ D Pro‐ β Phe ‐Leu‐Val‐Val‐OMe ( 1 ), Boc‐Leu‐Val‐ β Val ‐ D Pro‐Gly‐ β Leu ‐Val‐Val‐OMe ( 2 ), and Boc‐Leu‐Val‐ β Phe ‐Val‐ D Pro‐Gly‐Leu‐ β Phe ‐Val‐Val‐OMe ( 3 ). 500‐MHz 1 H‐NMR Analysis supports a preponderance of β ‐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 β ‐hairpin conformation with two β ‐residues occupying facing, non‐H‐bonded positions in antiparallel β ‐strands. Notably, β Val(3) adopts a gauche conformation about the C( α )C( β ) bond ( θ =+65°) without disturbing cross‐strand H‐bonding. The crystal structure of 2 , together with previously published crystal structures of peptides 3 and Boc‐ β Phe ‐ β Phe ‐ D Pro‐Gly‐ β Phe ‐ β Phe ‐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 β ‐residues can be accommodated into nucleating turn segments and into both the H‐bonding and non‐H‐bonding positions on the strands.