Functionally-important protein dynamics of photosensor proteins as revealed by time-resolved resonance Raman spectroscopy

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Functionally-important protein dynamics of some sensor proteins have been studied by time-resolved resonance Raman spectroscopy. Chief results are as follows.(1) Construction of a time-resolved ultraviolet resonance Raman spectrometer(2) Picosecond Protein Response to the Chromophore Isomerization of Photoactive Yellow Protein (PIP)Picosecond time-resolved ultraviolet resonance Raman (UVRR) spectra of PYP were measured. UVRR bands attributed to the vibration of tyrosine and tryptophan residues showed a spectral change upon photoreaction. It was found that the hydrogen-bond strength between the chromophore and Y42 increases in the pG* state. The ultrafast change in the tryptophan band revealed that a photo-induced structural change of the chromophore had propagated to the W119 region, located 12 A from the chromophore, within picoseconds.(3) Structural Dynamics of FixLon Signal Transduction and Ligand Discrimination FixLFixL is a heme-based O2 sensor protein, which responds to low O2 co … More ncentration by activating the transcriptional activator FixJ. Signal transduction is initiated by the dissociation of O2 from the sensor domain of FixL, resulting in protein conformational changes that are transmitted to a histidine kinase domain. To gain insight into the FixL sensing mechanism, we monitored changes in the protein's structure in the picosecond to millisecond timeframe, following the dissociation of the ligand using time-resolved resonance Raman spectroscopy. The FixL spectra show that there are three steps in the dynamic structural changes. Ligand-dependent structural dynamics are observed in the earliest step. Based on comparisons of these structural changes, a scheme for the signal transduction of FixL is proposed. Similar spectral changes were observed both for the sensor domain and for the full length protein, although structural changes occurred faster with the former than with the latter. This difference in rate suggests that the structural changes occurring in the heme pocket are coupled to those of the kinase domain. Less