New science exploration from XFEL : a new paradigm for structural visualisation of macromolecules

• Main Author: Gallagher-Jones, Marcus
• Published: University of Liverpool 2014
• Subjects: 570; QH301 Biology
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664325

X-rays have a long-standing history as an investigative probe in the sciences, and in particular their application to the biological and biomedical sciences has provided an enormous contribution to these fields. Indeed structural biology, the study of the molecules of life at an atomic scale via macromolecular crystallography, has been a major benefactor of advances in x-ray radiation sources. Currently two major bottlenecks exist within this field, the need for well diffracting crystals and radiation damage limitations. The advent of fourth generation x-ray sources, X-ray Free-electron Lasers (XFEL) heralds a shift in the way such experiments are performed. XFELs, due to their high brilliance and ultra short (fs) pulses, hope to decouple radiation dose limitations from spatial resolution by outrunning this radiation damage in short exposures, ‘diffraction before destruction’. This thesis is concerned with exploring experimental methodologies made possible by XFELs, including establishing the experimental infrastructure required at the worlds second XFEL, SACLA, and performing initial experiments. Firstly the potential of performing gas-phase small angle x-ray scattering experiments (gSAXS) is investigated. The current need for gas-phase structural information will be presented and the experimental parameters and projected signal requirements will then be explored. The results of experiments at a synchrotron radiation source with various biomolecules will be presented. It is shown that with the current experimental set-up experiments are fundamentally limited by the signal to noise ratio (SNR) pointing to the necessity of XFEL. Secondly the application of coherent diffractive imaging (CDI) to biological systems at synchrotron and XFEL sources is explored, and the development of experimental systems at both sources is outlined. A method for combining complimentary scattering experiments at both sources is demonstrated and the results of its application to the assembly mechanism of the self-assembling, non-crystalline, macromolecule, the RNAi microsponge, are presented. The microsponge is found to have a nucleating origin leading to a core-shell like nanostructure in the fully formed molecule.