Observation of Site-Resolved Vibrational Energy Transfer Using a Genetically Encoded Ultrafast Heater

摘要： Allosteric information transfer in proteins has been linked to distinct vibrational energy transfer (VET) pathways in a number of theoretical studies. Experimental evidence for such pathways, however, is sparse because site-selective injection of vibrational energy into a protein, i.e. localized heating, is required for their investigation. Here, we solve this problem by the site-specific incorporation of the non-canonical amino acid β-(1-azulenyl)-L-alanine (AzAla) via genetic code expansion. Being an exception to Kasha′s rule, AzAla undergoes ultrafast internal conversion and heating after S1 excitation while upon S2 excitation it serves as a fluorescent label. We endowed PDZ3, a protein interaction domain of postsynaptic density protein 95, with this ultrafast heater at two distinct positions. Using ultrafast IR spectroscopy, we could indeed observe VET from the incorporation sites in the protein to a bound peptide ligand on a picosecond timescale. This approach based on genetically encoded AzAla paves the way for detailed studies of VET and its role for function in a wide range of proteins.