Re-evaluation of protein neutron crystallography with and without X-ray/neutron joint refinement

Area of Science:

• Biochemistry
• Structural Biology
• Crystallography

Background:

• Protein neutron crystallography precisely determines hydrogen atom positions, vital for understanding enzyme mechanisms.
• Joint X-ray and neutron diffraction refinement is a powerful method for protein structure determination.

Purpose of the Study:

• To evaluate the impact of X-ray data on neutron diffraction data interpretation in joint refinement.
• To determine the necessity of joint X-ray/neutron refinement for accurate enzyme active site structure determination.

Main Methods:

• Comparative analysis of protein structure determination using neutron-only data versus joint X-ray/neutron data.
• Refinement of a bacterial copper amine oxidase crystal structure using both datasets.

Main Results:

• Most hydrogen and deuterium atoms were located similarly in both neutron-only and joint refinements.
• Joint refinement provided more accurate heavy-atom coordinates and improved neutron scattering density maps, particularly for the active-site cofactor.
• Neutron-only refinement was less effective for precise heavy-atom positioning.

Conclusions:

• Joint X-ray and neutron refinement is crucial for accurately determining the chemical structure of enzyme catalytic sites.
• This method enhances the reliability of structural information derived from neutron diffraction data.