Sub-3 Å resolution protein structure determination by single-particle cryo-EM at 100 keV

Cryoelectron microscopy (cryo-EM) has transformed structural biology by providing high-resolution insights into biological macromolecules. We report sub-3 Å resolution structures using the 100 keV Tundra cryo-TEM, equipped with the Falcon C direct electron detector (DED). This system combines advanced optics, extreme-brightness field emission gun (XFEG), and SP-TWIN lens to enhance coherence and resolution. The semi-automated loader reduced contamination and drift, enabling extended data collection, while the high detective quantum efficiency (DQE) of Falcon C improved signal-to-noise ratio. We validated performance by determining structures of biological samples, including apoferritin (2.1 Å), T20S proteasome (2.7 Å), GABA_A receptor (2.8 Å), hemoglobin (5.0 Å), transthyretin (3.5 Å), and AAV9 capsid (2.8 Å), spanning 50 kDa-3.9 MDa. This work highlights the potential of 100 keV transmission electron microscopes (TEMs) to make cryo-EM more accessible. It sets a precedent for using lower voltage TEMs not only for screening, but also for high-resolution protein structure determination.