NEW TECHNIQUES OF APPLYING MULTIWAVELENGTH ANOMALOUS SCATTERING DATA

Several different methods of using multi-wavelength anomalous scatteri ng data are described and illustrated by application to the solution o f the known protein structure, core streptavidin, for which data at th ree wavelengths were available. Three of the methods depend on the cal culation of Patterson-like functions for which the Fourier coefficient s involve combinations of the anomalous structure amplitudes from eith er two or three wavelengths. Each of these maps should show either vec tors between anomalous scatterers or between anomalous scatterers and non-anomalous scatterers. While they do so when ideal data are used, w ith real data they give little information; it is concluded that these methods are far too sensitive to errors in the data and to the scalin g of the data-sets to each other. Another Patterson-type function, the P(s) function, which uses only single-wavelength data can be made mor e effective by combining the information from several wavelengths. Two analytical methods are described, called AGREE and ROTATE, both of wh ich were very successfully applied to the core streptavidin data. They are both made more effective by preprocessing the data with a procedu re called REVISE which brings a measure of mutual consistency to the d ata from different wavelengths. The best phases obtained from AGREE le ad to a map with a conventional correlation coefficient of 0.549 and t his should readily be interpreted in terms of a structural model.