Séminaire Nano

Mardi 3 Février 2015 à 11h00.

Studying viral assemblies with mass spectrometry and XFELs

''Recent successes in femtosecond X-ray protein nano-crystallography and imaging of single particles demonstrate the prospects of X-ray free-electron lasers (XFELs) for biophysics. Due to the intense and short femtosecond pulses, diffraction patterns of a single particle can be recorded before damaging occurs. Thereby, the major bottleneck in structural biology to obtain large high quality crystals may be overcome. Since the sample is destroyed by the X-ray pulse, a full dataset is acquired in many shots of identical particles. The technique can be used to study structural changes in e.g. protein complexes in a time-resolved manner. However, current sample delivery techniques suffer from an increased background lowering the resolution or are in-efficient wasting precious samples. Moreover, the reconstruction of a single structure requires extensive computational sorting. Using native mass spectrometry (MS) for sample delivery, sample consumption would be reduced. Local increased concentrations of a sample can be achieved in ion traps to optimise the interaction rate with the FEL beam. MS is especially attractive for reaction monitoring as minor or transient species can be selected for imaging. With such an online purification, low populated species can be studied, which would otherwise pass unnoticed. Additional components, like ion mobility or dipole alignment, enable data pre-sorting according to shape and orientation. This could tremendously lower the computational costs to sort diffraction patterns and lead to orders of magnitude shorter calculation times. An introduction to XFELs, sample delivery systems and design considerations for the mass spectrometer are presented. Additionally, preliminary native MS data on processing and assembly of non-structural coronavirus proteins will be presented, which belong to the viral replication complex.''