Anchoring Sites of Fibrillogenic Peptide Hormone Somatostatin-14 on Plasmonic Nanoparticles

Abstract

International audienceDespite numerous investigations devoted to the control of peptide and protein self-assemblies using nanostructured materials, the molecular details of the peptide-material interaction sites remain still under debate. Here, we suggest a solution by using jointly the middle- and low wavenumber regions of surface-enhanced Raman spectra. To achieve our goal, adequately prepared gold and silver colloids, of which the nanofabrication was controlled by means of zeta potential and extinction spectra, were used to enhance the Raman signal arising from a natural fibrillogenic peptide hormone, somatostatin-14, at very low (10–6-to-10–8 M) concentrations. Transmission electron microscopy has revealed that the interacting partners are involved in a mutual aggregation process. In fact, while the presence of plasmonic colloids facilitates the aggregation of the peptide, leading to the formation of the so-called “corona” around nanoparticles, we could observe the appearance of relatively large size peptide-nanoparticle agglomerates in solution. However, the comparison between the data obtained from gold and silver nanoparticles is consistent with the fact that the nature of metal surface, as well as its ionic coverage, considerably affect the peptide binding and subsequent aggregation process. Furthermore, this work led us to conclude that the adsorption of somatostatin-14 on silver nanoparticles is rendered possible through an ionic pair interaction, whereas its anchoring on gold nanoparticles occurs by a direct binding, in which the metal atom and the nitrogen of the unique peptide tryptophan residue are involved

Large size citrate‐reduced gold colloids appear as optimal SERS substrates for cationic peptides

“…All the experiments were made at 25 °C on a NanoZS instrument (Malvern Instrument Ltd, Malvern, UK) in DTS1060 cuvettes. The measured electrophoretic mobility, μ e , for gold particles was then converted to z‐potential (ζ), following the procedure described recently . Then, the electrostatic potential of a particle type, ϕ(x), as a function of x, that is, distance from its surface, was estimated using the relation: , where k is the inverse of the Debye length (k −1 ), and ϕ(0) represents the electrostatic potential at the surface of the gold nanoparticle …”

“…However, the selection of the adequately sized gold particles for a specific application still remains under debate. For example, small and medium size NPs (10–40 nm particles) have been employed in drug delivery and control of protein fibrillogenesis, whereas SERS measurement on amino acids and peptide chains required larger size NPs . The latter NPs are presumably capable of forming the so‐called hot spots, that is, junctions and interspaces, in which electromagnetic radiation is strongly amplified .…”

“…For example, small and medium size NPs (10-40 nm particles) have been employed in drug delivery and control of protein fibrillogenesis, [23,26,27] whereas SERS measurement on amino acids and peptide chains required larger size NPs. [28,29] The latter NPs are presumably capable of forming the so-called hot spots, that is, junctions and interspaces, in which electromagnetic radiation is strongly amplified. [30,31] As far as the molecular species forming the coverage of AuNPs are concerned, recent studies based on attenuated total reflectance Fourier transform infrared absorption and X-ray photoelectron spectroscopy could provide valuable information on different H-bonding networks of citrate ions, [32] as well as on the chemical transformation of these anions to their oxidized anionic products.…”

Revealing the trehalose mediated inhibition of protein aggregation through lysozyme–silver nanoparticle interaction

“…Due to this surfaceselectivity, SERS has been exploited, by us and others, for protein based studies [37][38][39][40] and to detect minute structural changes on adsorption of proteins to the nanoparticle surface. 41 Here, SERS spectra with high signal-to-noise ratio were recorded from lysozyme-nanoparticle conjugates in the presence of 0M and 0.05M trehalose ( Figure 6A and B); however, the modes of lysozyme in 0.5M trehalose were not strongly enhanced ( Figure 6C).…”

“…In the presence of 0.05M trehalose, we also observe a feature at 1623 cm -1 , which may be ascribed to the presence of antiparallel β-sheets. 48 The disulphide and the Ag-N bonds 39,40,42,43,[46][47][48][49][50] The modes present in the spectrum of lysozyme alone in the absence of trehalose are marked with *.…”