Serial Femtosecond Crystallography of Optogenetic Function

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The ability to design synthetic light-sensitive materials that can be genetically encoded provides biologists the means and opportunity to sense and control biological function and environment. In order to learn how these materials function it has very recently become possible to make very fast 'snapshots' of the light-induced motions using X-ray crystallography, which is even possible for very short time scales that still involves the excited electrons (on femtosecond time scale). Novel 4th generation light sources can now be used to record such 'molecular movies' which is a breakthrough technology that we only very recently demonstrated. In the very near future we anticipate being able to record even better quality movies, as the European XFEL in Hamburg that allows much more data to be recorded will start user operation. Where previously we could only use laser spectroscopy techniques we can now actually 'watch' the very first motions of proteins directly after activation. It is known that the 'outcome' of biological reactions involving either sensing or activation (via 'actuation') is determined in these very first motions that occur on time scales typically less than picoseconds. For example, in the case of a bi-directional photochromic fluorescent protein the efficiency of switching in one direction is excellent at 30%, while the efficiency of switching in the reverse direction is poor at less than 0.05%, potentially limiting optogenetics applications. We are thus in a position to ask the question what determines this dramatic difference in the outcome of the reactions, and provide structural and dynamical information that will be highly valuable for feeding back for rational optogenetics design.