X-ray microdiffraction and conventional diffraction from frozen-hydrated biological specimens

Abstract

A system for recording microdiffraction patterns from micrometer-sized quick-frozen hydrated biological specimens at the high-flux beamline BL40XU of SPring-8 is described. The optics consists of a pair of pinholes drilled into tantalum substratum, with a defining aperture of diameter 2 μm. The frozen specimens are placed in an in-vacuum cryochamber mounted on a three-axis goniometer, where the specimens are stably held at a liquid-nitrogen temperature (∼74 K). A beam size of 1.5 μm (full width at half-maximum) is attained at the sample position. By using this system, diffraction patterns have been recorded from an isolated single myofibril (diameter ∼ 3 μm) of an insect flight muscle in an area equivalent to a single sarcomere (length ∼3 μm). The technique is potentially applicable to other micrometer-sized hydrated biological specimens, which are more susceptible to radiation damage than dry synthetic polymers or biopolymers. The quick-freezing of biological specimens has also been proven useful in reducing the specimen volume in the beam in conventional diffraction recordings. © 2005 International Union of Crystallography Printed in Great Britain - all rights reserved.