Protein Crystal Diffraction Patterns Using a Capillary-Focused Synchrotron X-ray Beam

A paraboloidally tapered glass monocapillary was used to focus an 8 keV monochromated synchrotron bending-magnet X-ray beam into a 40 (±5) μm focal spot located 45 (±5) mm from the exit of the capillary. This focal spot had a measured intensity gain of 120 (±10) times the intensity present in an equivalent cross section of the unfocused beam from the monochromator. This focused beam was used to obtain oscillation diffraction patterns on image plates from a hen egg-white lysozyme protein crystal in two distinct geometries: one with the specimen crystal at the capillary exit and the other with the crystal at the beam focus. In the first geometry, focused Bragg reflections were observed at the focal plane. In the second geometry, diverging Bragg reflections of high intensity from a small crystal volume were observed. Image-plate diffraction patterns for these two geometries were compared with exposures with equivalent integrated diffracted intensities obtained using a 100 × 100 μm unfocused X-ray beam with the same crystal. The use of the focused beam resulted in a reduction in the exposure time required to produce equivalent patterns by a factor of between 70 and 100.