A NEW SYNCHROTRON MAD DATA ACQUISITION METHOD: SIMULTANEOUS MULTI-WAVELENGTH ANOMALOUS DIFFRACTION (SMAD). Peter L. Lee* and Craig M. Ogata+, *Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, +Howard Hughes Medical Institute, X4, NSLS, Brookhaven National Laboratory, Upton, NY 11973

In recent years, Multi-wavelength Anomalous Diffraction (MAD) phasing has emerged to be a powerful synchrotron technique for solving protein crystal structures. However, a straight forward MAD data collection requires a stable crystal, synchrotron source, and beamline optics. The customized beamlines for fast energy changes, the improvement of flash freezing techniques and the availability of stable long lifetime synchrotron sources around the world have made MAD data measurement a more accessible experiment. Nevertheless, switching among different wavelengths to measure anomalous data sets is still very time consuming and puts great demands on the stability and reproducibility of the monochromator and the synchrotron beam.

We are here introducing a new synchrotron MAD data acquisition method, Simultaneous Multi-wavelength Anomalous Diffraction (SMAD), which can avoid switching energies. SMAD employs a variable bandwidth curved crystal monochromator (polychromator) coupled with an energy selecting grid plate. Our SMAD experiment demonstrates the ability to measure reflections at six different wavelengths and their Bijvoet pairs at the same time. On one diffraction image, we record both the dispersive and Bijvoet information from a myoglobin crystal for MAD phasing.

This work was carried out at both the X4A and the X6A beamlines, National Synchrotron Light Source, Brookhaven National Laboratory, which are supported by the Howard Hughes Medical Institute, and the Division of Materials Sciences and Chemical Sciences of DOE respectively.