High-resolution membrane protein structure by joint calculations with solid-state NMR and X-ray experimental data

Area of Science:

• Structural Biology
• Biophysics
• Biochemistry

Background:

• X-ray diffraction and Nuclear Magnetic Resonance (NMR) spectroscopy are primary methods for protein atomic structure determination.
• Challenges exist in resolving structures of large biomolecular assemblies and membrane proteins due to weak diffraction and NMR limitations.
• High-resolution structural data is crucial for understanding protein function and mechanisms.

Purpose of the Study:

• To develop and validate a hybrid method integrating solid-state NMR restraints with X-ray diffraction data.
• To improve the precision and quality of atomic models for protein structures, especially for difficult systems.
• To extend the applicability of structural biology techniques to weakly diffracting crystals and large protein complexes.

Main Methods:

• Incorporation of solid-state NMR restraints into conventional X-ray crystallography model building and refinement.
• Utilizing the DsbB-DsbA integral membrane protein complex as a test case for structural analysis.
• Comparative analysis of structural quality metrics before and after the addition of NMR restraints.

Main Results:

• Achieved a 0.92 Å backbone precision in the transmembrane region of DsbB-DsbA, a 58% improvement over X-ray data alone.
• Demonstrated a 22% increase in DsbB transmembrane residues occupying favored Ramachandran space compared to the crystal structure alone.
• Validated the method's effectiveness on a challenging integral membrane protein complex.

Conclusions:

• The hybrid method significantly enhances protein structure precision and quality.
• This approach is broadly applicable to protein systems with available X-ray data, especially those with weak diffraction.
• The integration of solid-state NMR and X-ray diffraction offers a powerful tool for advancing structural biology.