title: Role of a two-residue spacer in an alpha,beta-Didehydrophenylalanine containing hexapeptide: crystal and solution structure of Boc-val-deltaPhe-Leu-Ala-deltaPhe-Ala-OMe.
abstract: The peptide Boc-Val1-deltaPhe2-Leu3-Ala4-deltaPhe5-Ala6-OMe has been examined for the structural consequence of placing a two-residue segment between the deltaPhe residues. The peptide is stabilized by four consecutive beta-turns. The overall conformation of the molecule is a right-handed 3(10)-helix, with average (phi, psi) values (-67.7 degrees, -22.7 degrees), unwound at the C-terminus. The 1H NMR results also suggest that the peptide maintains its 3(10)-helical structure in solution as observed in the crystal state. The crystal structure is stabilized through head-to-tail hydrogen bonds and a repertoire of aromatic interactions laterally directed between adjacent helices, which are antiparallel to each other. The aromatic ring of deltaPhe5 forms the hub of multicentred interactions, namely as a donor in aromatic C-H...pi and aromatic C-H...O=C interactions and as an acceptor in a CH3...pi interaction. The present structure uniquely illustrates the unusual capability of a deltaPhe ring to host such concerted interactions and suggests its exploitation in introducing long-range interactions in the folding of supersecondary structures.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore 560012, India
authors.forename: Anil K
authors.initials: AK
authors.lastname: Padyana
authors.forename: S
authors.initials: S
authors.lastname: Ramakumar
authors.forename: Puniti
authors.initials: P
authors.lastname: Mathur
authors.forename: N R
authors.initials: NR
authors.lastname: Jagannathan
authors.forename: V S
authors.initials: VS
authors.lastname: Chauhan
mesh_terms: D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D010649:Phenylalanine / Q000031:analogs & derivatives*; D011487:Protein Conformation
chemical_list: D010455:Peptides; D010649:Phenylalanine