title: Alpha,beta-dehydro residues in the design of peptide and protein structures.
abstract: The results of X-ray studies on 19 structures containing dehydro residues have been analysed. The observed average C alpha = C beta distance in the dehydro residues is 1.331 (2) A. The average values of the C alpha = C beta - C gamma bond angle in dehydro-Phe and dehydro-Leu are 131.2 (2) and 127.3 (1) degrees, respectively. The dehydro residue is essentially planar. A beta-turn of type II is formed if the dehydro residue is placed either at the (i + 1) or at the (i + 2) corner position of the beta-turn. If the dehydro residues occur consecutively in an amino-acid sequence, the backbone folds into an alternating right- and left-handed alpha-helix. The peptide bond is planar in all these structures. The beta-turn is stabilized by an intramolecular hydrogen bond between CO of the ith and NH of the (i + 3)th residue.
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi.
authors.forename: T P
authors.initials: TP
authors.lastname: Singh
authors.forename: P
authors.initials: P
authors.lastname: Narula
authors.forename: H C
authors.initials: HC
authors.lastname: Patel
mesh_terms: D000595:Amino Acid Sequence; D007930:Leucine / Q000032:analysis; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry; D011487:Protein Conformation; D011506:Proteins / Q000138:chemical synthesis* / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D010455:Peptides; D011506:Proteins; D007930:Leucine