Thema der Dissertation:
Studying protein dynamics with X-ray free-electron lasers: Opportunities & Limitations
Studying protein dynamics with X-ray free-electron lasers: Opportunities & Limitations
Abstract: Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) allows unprecedented insight into protein dynamics by enabling time-resolved experiments at atomic spatial and femtosecond temporal resolution. However, the high intensity of the XFEL pulse destroys any sample that has been exposed to the focused beam such that a new protein crystal needs to be supplied for each pulse. This is typically achieved using a continuously flowing jet. To observe structural changes of light-triggered reactions, an optical pulse starts the reaction in crystals of photosensitive proteins and the X-ray pulse then interrogates the system after a given time interval.
For such experiments, there are two main issues: First, appropriate conditions have to be found for triggering the reaction of interest. I here establish experiments and calculations that accomplish this. Second, the measurement of weak signals is severely limited by the low data collection rate (≤ 120 Hz) at first-generation XFELs. Second-generation XFELs capable of generating X-ray pulses at MHz peak repetition rate promise to alleviate this issue. However, the short spacing between pulses introduces new challenges: it needs to be ensured that fresh sample is supplied sufficiently fast for each X-ray pulse. Moreover, it has been shown that the XFEL pulse launches shock waves in the jet, possibly affecting subsequent sample. Here, first experiments at MHz peak repetition rate were conducted, investigating whether data collection at these high speeds is possible and whether protein crystals may be damaged upon shock wave passage.
For such experiments, there are two main issues: First, appropriate conditions have to be found for triggering the reaction of interest. I here establish experiments and calculations that accomplish this. Second, the measurement of weak signals is severely limited by the low data collection rate (≤ 120 Hz) at first-generation XFELs. Second-generation XFELs capable of generating X-ray pulses at MHz peak repetition rate promise to alleviate this issue. However, the short spacing between pulses introduces new challenges: it needs to be ensured that fresh sample is supplied sufficiently fast for each X-ray pulse. Moreover, it has been shown that the XFEL pulse launches shock waves in the jet, possibly affecting subsequent sample. Here, first experiments at MHz peak repetition rate were conducted, investigating whether data collection at these high speeds is possible and whether protein crystals may be damaged upon shock wave passage.
Zeit & Ort
19.02.2021 | 10:00