Application of a multichannel position-sensitive X-ray detector to protein crystallography

A multichannel X-ray diffractometer is described, comprising a position-sensitive detector (xenon-filled proportional chamber, number of channels: 64 × 64, channel size: 2 × 2 mm), an Arndt-Wonacott oscillation camera, a digital processor for determining photon coordinates, and a number of computers for accumulation and processing of diffraction data and for control of the detector. The design allows the detector to be moved in the direction of the primary beam and at right angles to it. For a protein with a lattice constant of ~60 Å, the detector may simultaneously record only of the 2.5 Å diffraction pattern and has to be moved to record the full data. The diffractometer including this detector was constructed mainly to perfect the whole system of data collection, elaborate a set of programs and evaluate the accuracy. However it can be used to investigate medium-sized proteins with lattice constants of ~60 Å, with a resolution of 4.5 to 5 Å and a two- or three-fold gain in time over a standard diffractometer. Data are collected by the rotation method. One diffraction pattern corresponds to a crystal rotation of 0.5 to 1°. A series of successive patterns is recorded on disk. The squares of the structure factors are computed after the series is completed. The R value (reproducibility of the results) is 4-7%.