Direct phasing of one-wavelength anomalous-scattering data.

Area of Science:

• Crystallography
• Structural Biology
• Computational Chemistry

Background:

• Ab initio phasing is crucial for determining protein structures.
• One-wavelength anomalous scattering (SAS) offers a potential route for phasing.
• Developing efficient phasing methods is essential for structural biology.

Purpose of the Study:

• To survey and test ab initio phasing methods using one-wavelength anomalous scattering data.
• To evaluate the performance of the OASIS computer program on new datasets.
• To assess the feasibility of automated model fitting from generated electron density maps.

Main Methods:

• Application of the OASIS program for ab initio phasing.
• Utilizing one-wavelength anomalous scattering data from two protein datasets (OMPDC and PurE).
• Se atom location using the SAPI small-molecule program.
• Density modification techniques applied post-phasing.

Main Results:

• The OASIS program successfully determined phases for both OMPDC and PurE datasets.
• Electron density maps clearly showed the Calpha trace for both proteins.
• Most side-chains were resolved in the PurE electron density map.
• Phases were determined at approximately 2.5 A resolution for a large protein (OMPDC).

Conclusions:

• Ab initio phasing using single-wavelength anomalous scattering is effective for macromolecular crystallography.
• The OASIS program demonstrates robust performance in determining phases for large proteins.
• High-quality electron density maps suggest potential for fully automated model building.