Peak-shape analysis for protein neutron crystallography with position-sensitive detectors

Abstract

In neutron protein crystallography, the use of positionsensitive detectors controlled by a modern dataacquisition system permits new approaches to datacollection strategies. Instead of dealing with conventional scans, like the 0-20 scan, that provide an integrated intensity as a function of a rotational parameter, the computer-linked counter can be used to produce a three-dimensional reflection profile. As the crystal steps (AoJ) through a reflection, the observed data for each step are stored in an external memory as a function of extent in 20 and height (y) of a reflection. In this space, the reflection will be a three-dimensional distribution with dimensions determined by such basic geometrical conditions as A2, crystal size, mosaic spread, counter-resolution, and beam-collimation parameters. Knowledge of the interaction of these basic parameters will allow the design of optimal beam optics and will permit the delineation of the reflection from the background and permit, therefore, an accurate intensity determination.

The φ Extent of the Reflection Range in the Oscillation Method According to the Mosaicity-Cap Model

“…The effect of the beam divergence and wavelength spread can be represented by consideration of a nest of the Ewald spheres, rather than a single sphere (Arndt & Wonacott, 1977;Rossmann, Leslie, Abdel-Meguid & Tsukiha, 1979;Greenhough & Helliwell, 1982a,b;Schoenborn, 1983 Milch & Minor (1974), who consider one Ewald sphere but with a certain thickness. A similar concept is introduced by Kabsch (1988), who considers the distance between the reciprocal-lattice point and the surface of the Ewald sphere.…”

Neutron structure of the immunosuppressant cyclosporin A

“…Reflections in the blind region were collected by moving the/V axis to 90 ° and rotating around the to axis. The profile of the reflection on the two-dimensional position sensitive detector is dependent on experimental conditions (Schoenborn, 1983). The effects of beam divergence and wavelength spread, crystal size and mosaic, and detector resolution are convolved to produce the observed reflection profile.…”

An Algorithm for Automatic Mosaic Spread Analysis of a Protein Crystal

“…Various expressions for the angular width of the reflection have already been derived (Arndt & Wonacott, 1977;Schoenborn, 1983;Laktionov et al, 1989;Greenhough & Helliwell, 1982a;Bolotovsky & Coppens, 1997). Two new derivations, one purely geometrical and one purely analytical, are given here and compared to those that already exist.…”