Title
From bulk to plasmonic nanoparticle surface: behavior of two potent therapeutic peptides, octreotide and pasireotide
Author
Belén Hernández, Eduardo López-Tobar, Santiago Sanchez-Cortes, Yves-Marie Coïc, Bruno Baron, Alexandre Chenal, Sergei G Kruglik, Fernando Pflüger, Régis Cohen, Mahmoud Ghomi
Year
2016
Journal
Physical Chemistry Chemical Physics
Abstract
Octreotide and pasireotide are two cyclic somatostatin analogues with an important clinical use in the treatment and diagnosis of neuroendocrine tumors. Herein, by the joint use of several techniques (UV-visible absorption, fluorescence, circular dichroism, ζ-potential, transmission electron microscopy, Raman scattering, surface-enhanced Raman scattering, and quantum mechanical calculations) we have followed the structural dynamics of these analogues in the bulk, as well as their binding sites to plasmonic (gold and silver) colloids. In contrast to the previously derived conclusions, the two peptides seem to possess completely different conformational features. Octreotide, a cyclic octapeptide, is formed by a moderately flexible type-II’ β-turn maintained by a deformable disulfide linkage. Pasireotide, of which the cyclic character is made possible by peptide bonds, manifests a rigid backbone formed by two oppositely placed tight turns of different types, i.e. γ-turn and type-I β-turn. Owing to their cationic character, both analogues induce aggregation of negatively charged gold and silver colloids. Nevertheless, despite their notable structural differences, both peptides bind onto gold nanoparticles through their unique D-Trp residue. In contrast, their binding to silver colloids seems to be of electrostatic nature, as formed through monodentate or bidentate ionic pairs.
Instrument
J-810
Keywords
Circular dichroism, Secondary structure, Biochemistry