Free electron lasers (FELs) provide X-ray pulses in the femtosecond time
domain with up to 1012 higher photon flux than synchrotrons and open new avenues
for the determination of difficult to crystallize proteins, like large complexes and human
membrane proteins. While the X-ray pulses are so strong that they destroy any
solid material, the crystals diffract before they are destroyed. The most successful
application of FELs for biology has been the method of serial femtosecond crystallography
(SFX) where nano or microcrystals are delivered to the FEL beam in a stream of their mother liquid at room temperature,
which ensures the replenishment of the sample before the next X-ray pulse arrives. New injector technology allows
also for the delivery of crystal in lipidic cubic phases or agarose, which reduces the sample amounts for an SFX data
set by two orders of magnitude. Time-resolved SFX also allows for analysis of the dynamics of biomolecules, the proof of
principle being recently shown for light-induced reactions in photosystem II and photoactive yellow protein. An SFX data
sets consist of thousands of single crystal snapshots in random orientations, which can be analyzed now “on the fly” by
data analysis programs specifically developed for SFX, but de-novo phasing is still a challenge, that might be overcome
by two-color experiments or phasing by shape transforms.
Keywords: Femtosecond crystallography, free electron lasers, GPCRs, membrane proteins, photosystem I, photosystem II.
Rights & PermissionsPrintExport