Photon Science Seminar: "Time-resolved structural biology approaches to visualise photoreceptor proteins at work," Martin Weik, Institut de Biologie Structurale

Abstract
Photoreceptor proteins use light absorption to elicit a biological response in various processes such as vision, circadian rhythms and plant development. How the initial photochemical events at the receptor’s chromophore funnel through space and time into the desired photobiological event is a focus of intense current research.  

We focus on the CarH photoreceptor, an archetype of the newly discovered superfamily of B₁₂ dependent photoreceptors that surprisingly repurpose and finely tune the ubiquitous vitamin B₁₂ cofactor to sense light. CarH is a tetrameric light-responding repressor of carotenoid gene expression. Upon light-activation, structural changes lead to disassembly of the tetramer and its release from DNA to allow gene transcription. We combined time-resolved serial femtosecond crystallography at XFELs and time-resolved X-ray solution scattering at a synchrotron to study structural changes on the ns to s time-scale that lead from cleavage of the photolabile  chromophore bond to tetramer dissociation. Complementing the time-resolved structural  studies with results from cryo temperature-controlled X-ray crystallography and in crystallo  absorption spectroscopy, from various time-resolved and temperature-controlled  spectroscopies and from QM/MM calculations allowed providing and connecting essential pieces in the puzzle of B₁₂ dependent photoreception.