Experimental approaches for solution X-ray scattering and fiber diffraction

Abstract

X-ray scattering and diffraction from non-crystalline systems have gained renewed interest in recent years, as focus shifts from the structural chemistry information gained by high-resolution studies to the context of structural physiology at larger length scales. Such techniques permit the study of isolated macromolecules as well as highly organized macromolecular assemblies as a whole under near-physiological conditions. Time-resolved approaches, made possible by advanced synchrotron instrumentation, add a crucial dimension to many of these investigations. This article reviews experimental approaches in non-crystalline X-ray scattering and diffraction that may be used to illuminate important scientific questions such as protein/nucleic acid folding and structure-function relationships in large macromolecular assemblies.

Figure 1

HK97 bacterophage maturation kinetics studied by time-resolved solution x-ray scattering. A stopped-flow mixer (SF) initiates the maturation by a pH-jump, followed by a series of successive x-ray scattering pattern measurements. A synchrotron storage ring (SR) provides an intense x-ray beam. The direct beam is intercepted by a beam stop (blue disk) and surrounding circularly symmetric x-ray scattering is recorded as a function of time, and azimuthally averaged into one-dimensional patter as shown in the time course illustration. The peak position shifts toward small angle reflect the larger particle size in the final stage of the maturation. Courtesy of Dr. Kelly Lee, the Scripps Research Institute.

Figure 2

X-ray diffraction pattern from living Drosophila during tethered flight. The high intensity of the 19.3 nm first row line reflections (circles) indicates a high occupancy of actin binding sites by myosin heads poised for active contraction during the downstroke of the wingbeat.