Orientation and analysis of XFEL serial diffraction patterns from fibrous molecular assemblies

David H. Wojtas, Kartik Ayyer, Mengning Liang, Estelle Mossou, Carolin Seuring, V. Trevor Forsyth, Henry N. Chapman, Rick P. Millane

Abstract: The application of high-powered X-ray Free Electron Lasers (XFELs) in Serial Femtosecond Crystallography (SFX) has led to an increasing number of crystal structure determinations. Achieving the same success for systems of diminished crystallinity, such as fibrous systems and single particles, is inhibited by low signal strength and difficulties in orientating the data. We present methods developed for analyzing serial diffraction data from fibrous systems. The data are processed to identify cases where a single XFEL pulse intersects a single fibril. The fibril orientations are then determined by analysis of detected features within the diffraction data. With the fibril orientation determined, serial diffraction data is merged in 3D reciprocal space, allowing the individual structure amplitudes to be calculated. This allows structural studies of previously inaccessible fibrous systems to be performed, and represents a step closer towards the long-term goal of imaging single particles.