Phasing diffraction data from a stream of hydrated proteins

Abstract

We consider the problem of phase determination for continuous diffraction patterns obtained from a beam of identical, aligned large molecules (such as proteins), each coated with a layer of water or vitreous ice. Many laser-aligned molecules are assumed to lie within a wide continuous x-ray beam at any instant. An iterative phasing method is developed to extract the common target structure in three dimensions from diffraction patterns of these doped ice balls. Several measurements of the diffraction intensity in reciprocal space are needed. We found iteratively two boundaries (supports) (between protein and ice and the outer iceball support) by using the charge-flipping and multiple hybrid input-output algorithms, working with multiple sets of measured data. The approach is applied to simulated data from hydrated lysozyme proteins generated by the serial crystallography method of laser-aligned protein-beam diffraction proposed by Spence and Doak [Phys. Rev. Lett. 92, 198102 (2004)]. We consider also the effect of empty ice balls on the patterns. The algorithm can also be used to align images with different randomly chosen origins, so that the same embedded subunits overlap.