Structural transitions involved in a novel amyloid-like beta-sheet assemblage of tripeptide derivatives.
Self-assembly of two tripeptide derivatives containing three nonpolar isoleucine moieties and polar oxyethylene groups are studied in methanol. Peptide A [CH3(OCH2CH2)3OCH2CO(Ile)3OCH3] and peptide B [CH3(OCH2CH2)3OCH2CO(Ile)3NH (CH2CH2O)3CH3] take a mixture of unordered and helical conformation at low concentration (8.5 x 10(-4) M). However, at high concentration (2 x 10(-3) M), both the peptide showed significant increase in the helical conformation. An interesting conformational transition of peptides A and B at various methanol contents was observed in the solvated films of these compounds by spectroscopic methods like the far-uv circular dichroism and Fourier transform infrared (FT-IR) techniques. Peptide B, which contains more polar oxyethylene groups than A, showed a highly cooperative conformational transition when the methanol content was decreased. This transition was characterized by a large increase of beta-sheet, retaining a alpha-helical contribution. Peptide A showed a conformational transition resulting in a beta-sheet in the aggregated state. From the CD spectra, the ratio in the ellipticity indicates that peptide B forms twisted antiparallel beta-sheet conformation, whereas peptide A takes a parallel beta-sheet conformation. The results obtained in this work indicates the role of polar derivatization on the conformational preference of peptides having similar sequence.
Bio Organic Laboratory, Central Leather Research Institute, Adyar, Tamilnadu, Chennai-600 020, India.
S
S
Ganesh
R
R
Jayakumar
D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002942:Circular Dichroism; D009842:Oligopeptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
D016229:Amyloid beta-Peptides; D009842:Oligopeptides