Determination of polypeptide conformation in water with nanoscale resolution in water
Georg Ramer, Francesco Ruggeri, Aviad Levin, Toumas Knowles, Andrea Centrone
The conformational structure and folding of proteins are central to many biological processes. However, misfolding of proteins and peptides can lead to toxic aggregates that are involved in Alzheimers and other neurodegenerative disorders. Methods to determine the protein conformation with high spatial resolution and in their water-based environment are crucial to understand protein self-assembly, misfolding and neurodegeneration mechanisms. However, up to now, methods useful for characterizing the protein secondary structure (conformation) typically require complicated sample preparation or conditions vastly different from those in a cell or provide insufficient spatial resolution. Here we leverage the photothermal induced resonance technique to obtain, for the first time, high SNR (> 70) IR spectra in water and characterize individual fibrillar supramolecular nanoscale aggregates composed of diphenylalanine (FF) its tert-butoxycarbonyl (Boc)-modified derivative (Boc-FF). Experiments show that nanoscale IR absorption spectra and maps can be obtained in air and water with comparable SNR, and lateral resolution and reveal a pure β-sheet conformation for FF and both of α-helical and β-sheet conformations for Boc-FF at the individual fibril level.