Quantitative assessment of radiation damage in protein crystal

Abstract

Radiation damage is a well known phenomenon in the electron microscopic study of thin crystals of macromolecules. A quantitative description of radiation damage is essential for at least 3 reasons: (i) it can provide numerical parameters for evaluating the extent of specimen damage at various experimental conditions, (ii) it can provide an indicator as to the maximum number of diffraction patterns and images obtainable from a single crystal before the specimen is significantly altered, and (iii) since the specimen is being altered after the initial hit by the electrons, schemes are needed to make correction of the data prior to its use for structural calculation. This paper primarily deals with the methodology used to evaluate the quantitative aspects of radiation damage of thin protein crystals. The example of crystal used in this study was crotoxin complex embedded in glucose.A standard set of data recorded in a radiation damage study is a series of electron diffraction patterns from a single crystal. The important experimental variables include the exposure rate, the exposure time and the accumulating exposure between successive patterns.