Accuracy in Laue X-ray diffraction analysis of protein structures.

Area of Science:

• Crystallography
• Structural Biology
• Biophysics

Background:

• Protein structure determination is crucial for understanding biological function.
• Laue X-ray diffraction offers a polychromatic alternative to conventional monochromatic methods.
• Assessing the accuracy of Laue diffraction for protein structure analysis is essential.

Purpose of the Study:

• To investigate the accuracy of protein structure analysis using Laue X-ray diffraction.
• To compare the precision of Laue structure factors and electron-density map contrast with conventional methods.
• To evaluate the resolution achievable with Laue diffraction for bovine pancreatic trypsin (BPT) structures.

Main Methods:

• Analysis of two orthorhombic BPT structures.
• Utilizing precision in Laue structure factors and electron-density map contrast as criteria.
• Comparison with results from conventional crystal rotation methods.
• Data processing using the LAUEMAD program.
• Refinement of one BPT structure using Laue structure amplitudes.

Main Results:

• High resolution (around 1.4 Å) is achievable with both monochromatic and polychromatic (Laue) techniques.
• Electron-density maps calculated from Laue data exhibited significantly lower contrast.
• This lower contrast is attributed to inefficient exploration of reciprocal space at low resolution.
• Empirically derived wavelength scaling factors agreed well with theoretical estimates.
• A BPT structure was refined to 1.8 Å resolution with an R factor of 24% using Laue data.

Conclusions:

• Laue X-ray diffraction is a viable technique for high-resolution protein structure determination.
• Despite achieving high resolution, the contrast in electron-density maps is a limitation of the Laue method.
• Further optimization of Laue data collection and processing may improve map quality.