Lattice filter for processing image data of three-dimensional protein nanocrystals

Area of Science:

• Structural Biology
• Biophysics
• Microscopy

Background:

• Cryo-electron microscopy (cryo-EM) is crucial for determining the 3D structure of biological macromolecules.
• Obtaining high-resolution data from protein nanocrystals using cryo-EM can be challenging due to inherent low contrast in images.
• Existing methods may not fully exploit the information present in cryo-EM images of crystalline samples.

Purpose of the Study:

• To develop and validate a method for enhancing crystalline lattice information in cryo-EM images.
• To demonstrate the potential for high-resolution 3D structure determination from protein nanocrystals.
• To improve the signal-to-noise ratio and extract detailed structural data.

Main Methods:

• Acquisition of 300 kV cryo-electron microscopy images from thin (∼100 nm) protein nanocrystals using a Falcon 2 direct electron detector.
• Application of Fourier transformation to identify the crystalline lattice.
• Utilizing a wave finder combined with Wiener-type maximum-likelihood filtering to enhance lattice information.

Main Results:

• Fourier transformation revealed crystalline lattice information to surprisingly high resolutions, despite apparent lack of contrast in raw images.
• The implemented filtering procedure significantly enhanced the detectable lattice information.
• The method proved effective even for images that initially appeared featureless.

Conclusions:

• A novel image processing workflow can extract high-resolution structural information from low-contrast cryo-EM images of protein nanocrystals.
• This approach significantly improves the ability to determine the 3D structure of protein crystals.
• The findings pave the way for routine high-resolution cryo-EM structure determination of protein crystals.