Biological small-angle x-ray scattering facility at the Stanford synchrotron radiation laboratory

Beamline 4-2 at the Stanford Synchrotron Radiation Laboratory is a small-angle X-ray scattering/diffraction facility dedicated to structural studies on mostly noncrystalline biological systems. The instrument consists of a pinhole camera, which covers the magnitude of the scattering vector Q in the range 0.004-1.3 angstrom(-1) [Q = (4 pi/lambda)sin theta, where theta and lambda are one half of the scattering angle and the X-ray wavelength, respectively], and a Bonse-Hart geometry ultra-small-angle X-ray scattering setup for the Q range an order of magnitude smaller. The pinhole camera allows quick automated distance and detector selection among any combination of five distances and three position-sensitive detectors. The double-crystal monochromator can have either Si 111 crystals or a pair of synthetic multilayer diffractive elements for higher flux applications. We have adopted a suite of software originally developed for macromolecular crystallography for integrated beamline control as well as static and slow time-resolved small-angle scattering data collection. This article outlines recent technological developments and specialized instrumentation for conducting noncrystalline scattering experiments in structural biology at improved time and spatial resolutions.