Probing protein-peptide-protein molecular architecture by atomic force microscopy and surface plasmon resonance.

We demonstrate the creation of a protein multilayer which utilises the high affinity interaction between streptavidin and biotin and incorporates a peptidic spacer. Surface plasmon resonance measurements enabled us to monitor the construction of the multilayer in real time. Atomic force microscopy was utilised to determine surface functionality at each stage of the multilayer construction, allowing us to investigate the associated mechanical properties. In this context we observed an increase in biomolecular stretching on the formation of the multilayer. We demonstrate, utilising circular dichroism, that variations in the solvent can affect the secondary structure of the peptide linker and hence its mechanical properties. Trifluoroethanol titrations on the assembled system indicate that the multilayer properties are also stimuli responsive with regard to solvent conditions. These results indicate that the multilayer stretch before cleavage is increased in the presence of trifluoroethanol. This was not expected from the study of the individual linker alone, indicating the need to study the system as a whole as opposed to the isolated components.