This project involves both experimental and theoretical components. Multiple-wavelength diffraction data will be collected from a number of protein crystals selected for both the biological interest in the protein structures and the suitability for further developing the MAD phasing technique. This data will be collected at the Stanford Synchrotron Radiation Laboratory. Structure determination will proceed using MAD phase assignment and conventional crystallographic techniques. Refinements and extensions to the currently implemented MAD phasing algorithms will be developed in the course of the work. Drs. Merritt and Adman will evaluate the existing and newly developed MAD phasing algorithms by comparison of the resulting MAD phases and electron density maps against the corresponding phases and maps of the refined crystal structures. Multiple-Wavelength Anomalous Dispersion (MAD) phase assignment has recently been used successfully to determine the structure of several small proteins. An outstanding advantage of this novel technique is that structures may be determined using diffraction measurements from a single crystal of native protein. The method is based on measuring small changes in X-ray scattering amplitude as a function of X-ray wavelength. The eventual range of structure determinations for which it becomes the method of choice will depend on improving both experimental technique and data analysis to overcome the relatively small signal-to-noise ratio.***
