Self-assembly of the octapeptide lanreotide and lanreotide-based derivatives: the role of the aromatic residues.
We investigated the spectroscopic properties of the aromatic residues in a set of octapeptides with various self-assembly properties. These octapeptides are based on lanreotide, a cyclic peptide analogue of somatostatin-14 that spontaneously self-assembles into very long and monodisperse hollow nanotubes. A previous study on these lanreotide-based derivatives has shown that the disulfide bridge, the peptide hairpin conformation and the aromatic residues are involved in the self-assembly process and that modification of these properties either decreases the self-assembly propensity or modifies the molecular packing resulting in different self-assembled architectures. In this study we probed the local environment of the aromatic residues, naphthyl-alanine, tryptophan and tyrosine, by Raman and fluorescence spectroscopy, comparing nonassembled peptides at low concentrations with the self-assembled ones at high concentrations. As expected, the spectroscopic characteristics of the aromatic residues were found to be sensitive to the peptide-peptide interactions. Among the most remarkable features we could record a very unusual Raman spectrum for the tyrosine of lanreotide in relation to its propensity to form H-bonds within the assemblies. In Lanreotide nanotubes, and also in the supramolecular architectures formed by its derivatives, the tryptophan side chain is water-exposed. Finally, the low fluorescence polarization of the peptide aggregates suggests that fluorescence energy transfer occurs within the nanotubes.
Pandit
Anjali
A
IBITECS, CEA and CNRS, F-91191 Gif-sur-Yvette, France.
Fay
Nicolas
N
Bordes
Luc
L
Valéry
Céline
C
Cherif-Cheikh
Roland
R
Robert
Bruno
B
Artzner
Franck
F
Paternostre
Maïté
M
D000682:Amyloid / Q000737:chemistry; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D008956:Models, Chemical; D043942:Nanotubes / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods; D013053:Spectrophotometry / Q000379:methods; D013059:Spectrum Analysis, Raman / Q000295:instrumentation / Q000379:methods; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000737:chemistry
D000682:Amyloid; D010455:Peptides; D010456:Peptides, Cyclic; C060347:lanreotide; D014443:Tyrosine; D013004:Somatostatin; D014364:Tryptophan