Mini-beam collimator enables microcrystallography experiments on standard beamlines

Abstract

The high-brilliance X-ray beams from undulator sources at third-generation synchrotron facilities are excellent tools for solving crystal structures of important and challenging biological macromolecules and complexes. However, many of the most important structural targets yield crystals that are too small or too inhomogeneous for a 'standard' beam from an undulator source, $ 25-50 mm (FWHM) in the vertical and 50-100 mm in the horizontal direction. Although many synchrotron facilities have microfocus beamlines for other applications, this capability for macromolecular crystallography was pioneered at ID-13 of the ESRF. The National Institute of General Medical Sciences and National Cancer Institute Collaborative Access Team (GM/CA-CAT) dual canted undulator beamlines at the APS deliver high-intensity focused beams with a minimum focal size of 20 mm  65 mm at the sample position. To meet growing user demand for beams to study samples of 10 mm or less, a 'mini-beam' apparatus was developed that conditions the focused beam to either 5 mm or 10 mm (FWHM) diameter with high intensity. The mini-beam has a symmetric Gaussian shape in both the horizontal and vertical directions, and reduces the vertical divergence of the focused beam by 25%. Significant reduction in background was achieved by implementation of both forward-and back-scatter guards. A unique triple-collimator apparatus, which has been in routine use on both undulator beamlines since February 2008, allows users to rapidly interchange the focused beam and conditioned mini-beams of two sizes with a single mouse click. The device and the beam are stable over many hours of routine operation. The rapid-exchange capability has greatly facilitated sample screening and resulted in several structures that could not have been obtained with the larger focused beam.

Radiation damage in protein crystals is reduced with a micron-sized X-ray beam

“…S1). Beam sizes between 5 and 15 μm with a nearly circular cross-section were achieved by using minibeam collimators (20) in combination with focusing mirrors (Table S1). For beam sizes less than 5 μm, circular Fresnel zone plate optics (34) were used to focus the beam at the sample position.…”

“…Monte Carlo simulations of photoelectron trajectories predicted that the greatest energy deposition in the photoelectron flight path was a few microns from the photoelectron origin, and that the photoelectrons would escape the illuminated crystal volume if the crystal (18) or the beam (19) were small relative to the photoelectron path length. Thus, there is a potential for reducing radiation damage if the incident X-ray beam size is decreased beyond the microbeams now in use, which are as small as 5-10 μm (20)(21)(22). Photoelectron transfer of energy out of the beam footprint causing "penumbral damage" is well known in radiology and has been observed in studies with high-energy (MeV) X-rays (23).…”

Terminal Alkene Formation by the Thioesterase of Curacin A Biosynthesis

“…Among 25 SeMet TE crystals, only one diffracted beyond 4 Å, but was visibly two crystals and had multiple lattices in the diffraction pattern. A region visually identified as a single crystal was probed in three 10-m steps using a 20-m mini-beam (22). The crystal was centered at the position with the strongest diffraction and the least interference from the second lattice, and Friedel data were collected in inverse-beam geometry ( .…”

Macromolecular crystallography at synchrotron radiation sources: current status and future developments

“…Diffraction quality of a crystal may vary over different regions. At the microfocus beamlines (discussed later) or those with mini-beam collimation to provide a small beam (Cherezov et al 2009;Fischetti et al 2009), it is possible to scan small areas within larger crystals to detect the best portion of the crystal for diffraction (Aishima et al 2010).…”