Cryo-EM of soft-landedβ-galactosidase: Gas-phase and native structures are remarkably similar

Native mass spectrometry (native MS) is a powerful technique that provides information on stoichiometry, interactions, homogeneity and shape of protein complexes. However, the extent of deviation between protein structures in the mass spectrometer and in solution remains a matter of debate. Here, we uncover the gas-phase structure of β -galactosidase using single particle electron cryomicroscopy (cryo-EM) down to 2.6 Å resolution, enabled by soft-landing of mass-selected protein complexes onto cold TEM grids and in-situ ice coating. We find that large parts of the secondary and tertiary structure are retained from solution, with dehydration-driven subunit reorientation leading to consistent compaction in the gas phase. Our work enables visualizing the structure of gas-phase protein com-plexes from numerous experimental scenarios at side-chain resolution and demonstrates the possibility of more controlled cryo-EM sample preparation. One Sentence Summary Electrospray ion-beam deposition on cold grids and in-vacuum ice growth enable cryo-EM of mass-selected proteins at 2.6 Å.