Protein electrostatic potential Fourier maps calculated using the transferable aspherical atom model and the...

Area of Science:

• Structural Biology
• Biophysics
• Computational Chemistry

Background:

• Lower resolution maps from cryo-electron microscopy (cryo-EM) and electron diffraction typically contain less information.
• However, charged moieties in molecules appear more prominent in lower resolution maps.

Purpose of the Study:

• To theoretically investigate how truncating high-resolution data affects Fourier images of protein crystal electrostatic potential.
• To compare the effects on electrostatic potential maps versus electron density maps using different scattering factor models.

Main Methods:

• Analyzed theoretical Fourier images of protein crystal electrostatic potential by truncating data from 1 Å to 8 Å.
• Utilized the independent atom model (IAM) and the transferable aspherical atom model (TAAM) with UBDB/MATTS data.
• Compared results with theoretical Fourier images of electron density maps from X-ray diffraction.

Main Results:

• When using IAM, electrostatic potential and electron density maps showed little difference across resolutions.
• TAAM-based electrostatic potential maps at lower resolutions significantly differed from electron density maps, especially at charged moieties.
• The difference between TAAM and IAM was most pronounced in lower resolution electrostatic potential maps, varying with atom type and charge.

Conclusions:

• Accurate scattering factors (like TAAM) are essential for interpreting low-resolution electrostatic potential maps of charged systems.
• The choice of scattering factor model significantly impacts the interpretation of charged moieties in lower resolution structural data.
• This highlights the importance of using appropriate models for accurate structural analysis, particularly for charged regions.