Application of Alanine Scanning to Determination of Amino Acids Essential for Peptide Adsorption at the Solid/Solution Interface and Binding to the Receptor: Surface-Enhanced Raman/Infrared Spectroscopy versus Bioactivity Assays

The article describes
the application of the alanine-scanning technique
used in combination with Raman, surface-enhanced Raman, attenuated
total reflection Fourier transform infrared, and surface-enhanced
infrared absorption (SEIRA) spectroscopies, which allowed defining
the role of individual amino acid residues in the C-terminal 6–14 fragment of the bombesin chain (BN6–14) on the path of its adsorption on the surface of Ag (AgNPs) and
Au nanoparticles (AuNPs). A reliable analysis of the SEIRA spectra
of these peptides was possible, thanks to a curve fitting of these
spectra. By combining alanine-scanning with biological activity studies
using cell lines overexpressing bombesin receptors and the intracellular
inositol monophosphate assay, it was possible to determine which peptide
side chains play a significant role in binding a peptide to membrane-bound
G protein-coupled receptors (GPCRs). Based on the analysis of spectral
profiles and bioactivity results, conclusions for the specific peptide–metal
and peptide–GPCR interactions were drawn and compared.