MOTIVATION: Cryogenic electron microscopy (cryo-EM) is a core experimental technique used to determine the structure of macromolecules such as proteins. However, the effectiveness of cryo-EM is often hindered by the noise and missing density values in cryo-EM density maps caused by experimental conditions such as low contrast and conformational heterogeneity. Although various global and local map-sharpening techniques are widely employed to improve cryo-EM density maps, it is still challenging to efficiently improve their quality for building better protein structures from them. RESULTS: In this study, we introduce CryoTEN-a 3D UNETR++ style transformer to improve cryo-EM maps effectively. CryoTEN is trained using a diverse set of 1295 cryo-EM maps as inputs and their corresponding simulated maps generated from known protein structures as targets. An independent test set containing 150 maps is used to evaluate CryoTEN, and the results demonstrate that it can robustly enhance the quality of cryo-EM density maps. In addition, automatic de novo protein structure modeling shows that protein structures built from the density maps processed by CryoTEN have substantially better quality than those built from the original maps. Compared to the existing state-of-the-art deep learning methods for enhancing cryo-EM density maps, CryoTEN ranks second in improving the quality of density maps, while running >10 times faster and requiring much less GPU memory than them. AVAILABILITY AND IMPLEMENTATION: The source code and data are freely available at https://github.com/jianlin-cheng/cryoten.

SUMMARY: Robust, flexible and fast software to read, write and manipulate macromolecular structures is a prerequisite for productively doing structural bioinformatics. We present BioStructures.jl, the first dedicated package in the Julia programming language for dealing with macromolecular structures and the Protein Data Bank. BioStructures.jl builds on the lessons learned with similar packages to provide a large feature set, a flexible object representation and high performance. AVAILABILITY AND IMPLEMENTATION: BioStructures.jl is freely available under the MIT license. Source code and documentation are available at https://github.com/BioJulia/BioStructures.jl. BioStructures.jl is compatible with Julia versions 0.6 and later and is system-independent. CONTACT: [email protected].