Mask-based approach to phasing of single-particle diffraction data. II. Likelihood-based selection criteria.

Area of Science:

• Crystallography
• Structural Biology
• Biophysics

Background:

• Mask-based phasing is a crucial technique in solving the phase problem in crystallography.
• Traditional methods often struggle with accurate phase determination, especially for high-resolution data.

Purpose of the Study:

• To introduce a new likelihood-based selection criterion for mask-based phasing.
• To improve the accuracy of phase determination and resolution estimation in crystallographic studies.

Main Methods:

• Generating numerous molecular masks and evaluating their likelihood based on reproducing observed structure-factor magnitudes.
• Applying a likelihood-based selection rule that gives higher weight to weak, high-resolution reflections.
• Testing the method on simulated single-particle diffraction data of photosystem II monomer.

Main Results:

• The new criterion successfully phased simulated data, yielding a 16 Å resolution Fourier synthesis with high correlation to the exact phase set.
• Accurate phasing was achieved for high-resolution reflections, outperforming traditional correlation coefficient methods.
• Model-trapping analysis indicated that the standard '50% shell correlation' criterion might overestimate achieved resolution.

Conclusions:

• The likelihood-based mask-selection criterion is effective for mask-based phasing, enhancing accuracy and reliability.
• This approach offers a more robust method for estimating the resolution achieved in crystallographic experiments.
• The findings have significant implications for advancing macromolecular structure determination.