Multiwavelength anomalous diffraction analysis at the M absorption edges of uranium

Area of Science:

• Macromolecular Crystallography
• Structural Biology
• Biophysics

Background:

• Multiwavelength anomalous diffraction (MAD) is crucial for macromolecular crystallography.
• Previous MAD phasing utilized K or L absorption edges of various elements.
• Uranium's anomalous scattering properties at M-edges were unexplored for MAD phasing.

Purpose of the Study:

• Investigate uranium's anomalous scattering at M(IV) and M(V) edges for MAD phasing.
• Assess the feasibility of using uranium for phasing large macromolecular assemblies.

Main Methods:

• Measured fluorescence spectra to determine uranium's anomalous scattering factors (f', f").
• Conducted MAD experiments using uranyl nitrate-derivatized porcine elastase crystals.
• Collected a four-wavelength MAD data set at the M(IV) edge to 3.2-A resolution.

Main Results:

• Uranium exhibited exceptionally strong anomalous scattering at M(IV) and M(V) edges.
• MAD data collection and analysis yielded accurate phase information (32° phase difference).
• An interpretable electron-density map was generated from the collected data.

Conclusions:

• Uranium is a potent anomalous scatterer for MAD phasing at its M-edges.
• Current instrumentation can effectively collect diffraction data at these low-energy edges.
• Uranium-based MAD phasing shows promise for very large macromolecular structures.