Crystal structure of Boc-LAla-deltaPhe-deltaPhe-deltaPhe-deltaPhe-NHMe: a left-handed helical peptide.
Alpha,beta-dehydrophenylalanine residues constrain the peptide backbone to beta-bend conformation. A pentapeptide containing four consecutive (deltaPhe) residues has been synthesised and crystallised. The peptide Boc-LAla-deltaPhe-deltaPhe-deltaPhe-deltaPhe+ ++-NHMe (C45H46N6O7, MW = 782.86) was crystallised from an acetonitrile/methanol mixture. The crystal belongs to the orthorhombic space group P2(1)2(1)2(1) with a = 19.455(6), b = 20.912(9), c = 11.455(4) A and Z = 4. The X-ray (MoKalpha, lambda = 0.7107 A) intensity data were collected using the Rigaku-AFC7 diffractrometer. The crystal structure was determined by direct methods and refined using the least-squares technique, R = 8.41% for 1827 reflections with absolute value of Fo > 4sigma(absolute value of Fo). The molecule contains the largest stretch of consecutive dehydrophenylalanine residues whose crystal structure has been determined so far. The peptide adopts left-handed 3(10)-helical conformation despite the presence of LAla at the N-terminus. The mean phi, psi values, averaged across the last four residues are 56.8 degrees and 17.5 degrees, respectively. There are four 4-->1 intramolecular hydrogen bonds, characteristic of the 310-helix. In the crystal each molecule interacts with four crystallographically symmetric molecules with one hydrogen bond each.
Department of Physics, Indian Institute of Science, Bangalore.
U A
UA
Ramagopal
S
S
Ramakumar
R M
RM
Joshi
V S
VS
Chauhan
D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D009842:Oligopeptides / Q000737:chemistry*; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary
D009842:Oligopeptides; C116116:tert-butyloxycarbonylalanyl-phenylalanyl-phenylalanyl-phenylalanyl-phenylalaninamide; D010649:Phenylalanine; C018632:phenyldehydroalanine