Time-Resolved Serial Femtosecond Crystallography at the European XFEL

The European XFEL (EuXFEL) is a 3.4 km long X-ray source, which produces femtosecond, ultra-brilliant and spatially coherent X-ray pulses at megahertz repetition rates. This X-ray source has been designed to enable the observation of ultrafast processes with near-atomic spatial resolution. Time-resolved crystallographic investigations on biological reactions constitute a particularly important class of experiments with biomedical and health related implications. Due to the unusual X-ray pulse structure, such an experiment is challenging. Here we demonstrate how a biological reaction can be followed on ultrafast time scales at the EuXFEL. We investigate the picosecond time range in the photocycle of photoactive yellow protein (PYP) with MHz X-ray pulse rates. We show that difference electron density maps of excellent quality can be obtained. Results connect the previously explored femtosecond PYP dynamics to time scales accessible at synchrotrons. This opens the door to a wide range of time resolved studies at the EuXFEL.