Improved joint X-ray and neutron refinement procedure in Phenix.

Area of Science:

• Crystallography
• Structural Biology
• Biophysics

Background:

• Neutron diffraction is crucial for determining atomic structures, especially hydrogen positions and protonation states.
• Neutron diffraction data quality is often inferior to X-ray diffraction data due to technical limitations.
• Joint X-ray and neutron (XN) refinement typically uses a single model, assuming data isomorphism.

Purpose of the Study:

• To address limitations in current joint XN refinement methods.
• To introduce and test a novel joint XN refinement approach optimizing separate models.
• To investigate the impact of hydrogen atom refinement strategies (riding vs. individual).

Main Methods:

• Development of a new joint XN refinement method optimizing distinct models for X-ray and neutron data.
• Testing the new method using existing neutron models and data from the Protein Data Bank.
• Comparative analysis of four separately re-refined neutron models to identify limitations.

Main Results:

• The new joint XN refinement method demonstrates improved structural determination capabilities.
• The study highlights limitations of traditional joint XN refinement approaches.
• The efficacy of different hydrogen atom refinement strategies was evaluated.

Conclusions:

• The proposed joint XN refinement method offers a more robust approach to solving crystallographic structures.
• This advancement is particularly beneficial for structures with challenging neutron diffraction data.
• Further investigation into hydrogen atom treatment in refinement is warranted.