Single-particle cryo-EM

Single-particle cryo-EM
Name	Single-particle cryo-EM
Classification	Structural biology technique
Invented by	Richard Henderson, Jacques Dubochet, Joachim Frank
Year	1980s–2010s
Applications	Structural determination of macromolecules, drug discovery

Single-particle cryo-EM Single-particle cryo-EM is a technique for determining three-dimensional structures of macromolecules by imaging vitrified particles with an electron microscope, enabling near-atomic models that inform biochemistry and pharmacology. Pioneering work by Richard Henderson, Jacques Dubochet, and Joachim Frank led to methodological advances adopted widely across laboratories, industrial research centers such as Genentech and facilities like the European Synchrotron Radiation Facility. Major developments in detectors and algorithms have involved companies and institutions including Gatan, Thermo Fisher Scientific, University of Cambridge, and Max Planck Institute.

Introduction

Single-particle cryo-EM grew from efforts in the 1970s and 1980s to image macromolecules with transmission electron microscopes such as those produced by JEOL and FEI Company, later acquired by Thermo Fisher Scientific. Early champions including Richard Henderson and Joachim Frank combined physics from Erwin Schrödinger's era with computational advances at places like Massachusetts Institute of Technology and Columbia University to produce class averages and reconstructions. The so-called "resolution revolution" in the 2010s was driven by direct electron detectors developed at companies like Gatan and algorithmic innovations from groups at MRC Laboratory of Molecular Biology and Harvard University. Award recognition included the Nobel Prize for work enabling broader adoption.

Principles and methodology

The method images many copies of a macromolecular complex adsorbed to a grid, then computationally aligns projections to produce a 3D reconstruction, integrating concepts from microscopy and inverse problems studied at California Institute of Technology and Massachusetts Institute of Technology. Electron optics developed at manufacturers such as Zeiss and Hitachi determine contrast transfer functions, while statistical frameworks pioneered by researchers affiliated with Princeton University and University of California, San Francisco underpin maximum-likelihood refinement and Bayesian approaches. Software packages originating from labs at Columbia University and MRC Laboratory of Molecular Biology implement these methodologies and are used alongside modeling platforms from UCSF and European Bioinformatics Institute.

Sample preparation and vitrification

Specimens are applied to support films on grids manufactured by firms such as Quantifoil and plunge-frozen in liquid ethane cooled by liquid nitrogen, techniques refined in the laboratory of Jacques Dubochet and adopted in facilities like Brookhaven National Laboratory. Cryo-plungers produced by companies including Leica Microsystems are standard tools, while automation and robotic platforms from Tecan and academic groups at ETH Zurich enable high-throughput screening. Optimization of buffer conditions, detergents, and nanodisc systems draws on research from institutions such as Scripps Research and University of Oxford and is critical for preserving native conformations.

Image acquisition and instrumentation

Data collection uses transmission electron microscopes made by Thermo Fisher Scientific (FEI), JEOL, and Hitachi equipped with energy filters from Gatan and direct electron detectors developed by Direct Electron and Gatan. High-end microscopes are housed in national centers like Diamond Light Source and National Institute of Health-supported facilities, and are maintained according to specifications influenced by instrument teams at Thermo Fisher Scientific and JEOL. Automation suites and data management systems developed at European Synchrotron Radiation Facility and Stanford University coordinate dose-fractionation, beam-tilt compensation, and stage stability to maximize throughput.

Image processing and 3D reconstruction

Recorded micrographs undergo motion correction, CTF estimation, particle picking, 2D classification, 3D initial model generation, and iterative refinement using software such as RELION (developed at MRC Laboratory of Molecular Biology), cryoSPARC (from Structura Biotechnology founders with ties to Massachusetts Institute of Technology), and EMAN (originating at University of California, San Francisco). Algorithmic contributions from groups at Princeton University, University of Cambridge, and Broad Institute address heterogeneity using multibody refinement and 3D variability analysis, while high-performance computing resources at Lawrence Berkeley National Laboratory and Argonne National Laboratory accelerate large-scale reconstructions.

Resolution, validation, and model building

Resolution assessment relies on gold-standard Fourier shell correlation (FSC) criteria established through community consensus involving investigators at MRC Laboratory of Molecular Biology and UCSF, while local resolution metrics and map sharpening protocols were developed by teams at University of Oxford and Columbia University. Model building into maps employs tools from University of California, San Francisco and European Bioinformatics Institute such as Phenix and Coot, and model validation workflows reference standards advocated by the Protein Data Bank and structural validation groups at EMDataResource and RCSB PDB. Community initiatives led by International Union of Crystallography and national academies promote reproducibility.

Applications and impact in structural biology

Single-particle cryo-EM has elucidated structures of viral capsids studied at Centers for Disease Control and Prevention, membrane proteins including G protein-coupled receptors analyzed by teams at Genentech and Scripps Research, and large assemblies such as ribosomes characterized by groups at MRC Laboratory of Molecular Biology and Max Planck Institute; these findings influenced vaccine design efforts at institutions like National Institutes of Health and pharmaceutical companies such as Pfizer and Moderna. Structural insights from work at Harvard University, Stanford University, and University of California, San Diego have guided drug-discovery campaigns and mechanistic studies across cell biology and biotechnology sectors.

Limitations and challenges

Challenges include particle preferred orientation problems documented by researchers at Columbia University and University of Oxford, beam-induced motion studied at Lawrence Berkeley National Laboratory, and difficulties in resolving small proteins noted by groups at University of Cambridge and Princeton University. Access to high-end microscopes is constrained at many institutions despite investments by national facilities such as Diamond Light Source and European Synchrotron Radiation Facility, and training pipelines run through graduate programs at Massachusetts Institute of Technology and ETH Zurich are required to build expertise. Continued progress depends on collaborations between academia, industry, and infrastructure providers like Thermo Fisher Scientific and Gatan.

Category:Electron microscopy