Crystallography without crystals I: the common-line method for assembling a 3D intensity volume from single-particle scattering

Shneerson, V. L.
Ourmazd, A.
Saldin, D. K.
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We demonstrate that a common-line method can assemble a 3D oversampled diffracted intensity distribution suitable for high-resolution structure solution from a set of measured 2D diffraction patterns, as proposed in experiments with an X-ray free electron laser (XFEL) (Neutze {\it et al.}, 2000). Even for a flat Ewald sphere, we show how the ambiguities due to Friedel's Law may be overcome. The method breaks down for photon counts below about 10 per detector pixel, almost 3 orders of magnitude higher than expected for scattering by a 500 kDa protein with an XFEL beam focused to a 0.1 micron diameter spot. Even if 10**3 orientationally similar diffraction patterns could be identified and added to reach the requisite photon count per pixel, the need for about 10**6 orientational classes for high-resolution structure determination suggests that about ~ 10**9 diffraction patterns must be recorded. Assuming pulse and read-out rates of 100 Hz, such measurements would require ~ 10**7 seconds, i.e. several months of continuous beam time.
Comment: 27 pages, 9 figures
Quantitative Biology - Biomolecules