A Guide to time-resolved structural analysis of light-activated proteins

Dynamical changes in protein structures are essential for protein function and occur over femtoseconds to seconds timescales. X-ray free electron lasers have facilitated investigations of structural dynamics in proteins with unprecedented temporal and spatial resolution. Light-activated proteins are attractive targets for time-resolved structural studies, as the reaction chemistry and associated protein structural changes can be triggered by short laser pulses. Proteins with different light-absorbing centres have evolved to detect light and harness photon energy to bring about downstream chemical and biological output responses. Following light absorption, rapid chemical/small-scale structural changes are typically localised around the chromophore. These localised changes are followed by larger structural changes propagated throughout the photoreceptor/photocatalyst that enables the desired chemical and/or biological output response. Time-resolved serial femtosecond crystallography (SFX) and solution scattering techniques enable direct visualisation of early chemical change in light-activated proteins on timescales previously inaccessible, whereas scattering gives access to slower timescales associated with more global structural change. Here, we review how advances in time-resolved SFX and solution scattering techniques have uncovered mechanisms of photochemistry and its coupling to output responses. We also provide a prospective on how these time-resolved structural approaches might impact on other photoreceptors/photoenzymes that have not yet been studied by these methods.

Automated summary

Dynamic changes in protein structures are crucial for protein function and can be investigated with unprecedented temporal and spatial resolution using X-ray free electron lasers. Light-activated proteins are attractive targets for time-resolved structural studies, as they allow for visualization of early chemical changes and global structural changes.