Enhancing Lab Source Anomalous Scattering Using Cr Kα Radiation for Its Potential Application in Determining Macromolecular Structures

Abstract

Obtaining phase information for the solution of macromolecu lar structures is a bottleneck in X-ray crystallography. Anomalous dispersion was recognized as a powerful tool for phasing macromolecular structures. It was used mainly to supplement the isomorphous replacement or to locate the anomalous scatterer itsel f. The first step in solving macro- molecular structures by SAD (single-wavelength anomalous diff raction) is the location of the anomalous scatterers. The SAD method for experimental phasin g has evolved substantially in th e recent years. A phasing tool, 5 -amino- 2,4,6 - triiodoisophthalic acid (I3C—magic triangle), was incorporated into th ree proteins, lysozyme, glucose isomerase and thermolysin using quick-soaking and co-crystallization method in order to understand the binding of metal ion with proteins. The high quality of the diffraction data, the use of chromium anode X-ray radiation and the required amount of anomalous signal enabled way for successful structure determination and automated model building. An analysis and/or comparison of the sulfur and iodine anomalous signals at the Cr K α wavelength are discussed.