Spatio-temporal observation of structural changes in the optogenetic proteins halorhodopsin and YF1

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The goal of this project is the achievement of an atomic level understanding of the reaction mechanism of light switching in proteins. Reaching this objective requires a methodology with acute sensitivity and sufficient time-resolution. These requirements are met by vibrational spectroscopy. The structural changes are associated with vibrational changes of the chromophore, the protein backbone and amino acid side chains. Even minute alterations in hydrogen-bonding or protonation states are resolved by IR difference spectroscopy. We have developed surface-enhanced IR difference spectroscopy (SEIDAS) to apply this novel approach to monolayers of electron- as well as light-driven proteins. The methodology is able to monitor the impact of the electric field (or the membrane potential) on the functionality of the protein with atomis tic sensitivity (“voltage-clamp with infrared detection”). The IR data will be compared to surfaceenhanced resonance Raman spectroscopy (SERRS) which is selective for the vibrational modes of the chromophore, only. Primary target systems are the channelrhodopsins (ChR1 and ChR2 from Chlamydomonas reinhardtii and from Volvox carteri) which are light-gated ion channels. SEIDAS will provide molecular information on the gating mechanism which is regulated by the membrane potential. We are not only intensely collaborating with the groups that use electrophysiological techniques (Gottschalk, Hegemann, Nagel) but take advantage of the color tuning approaches developed by the Elstner & Hegemann group. We will continue our vibrational spectroscopic studies on the blue-light photoreceptors LOV and BLUF which will be expanded to include Aureochrome and PAC (in collaboration with the Hegemann, Nagel, Schlichting and Schwärzel groups).