Cryo-EM image acquisition was performed on a JEM-2200FS transmission electron microscope (JEOL, Tokyo, Japan) at the National Center for High-Resolution Electron Microscopy (nCHREM) at Lund University. The microscope was equipped with a field-emission electron source, a cryo pole piece in the objective lens, and an in-column energy filter (omega filter). Zero-loss images were recorded at an acceleration voltage of 200 kV on a TemCam-F416 camera (TVIPS) using SerialEM under low-dose conditions.
Samples were prepared using an automatic plunge freezer system (Leica EM GP, Wetzlar, Germany) with the environmental chamber set to 21 °C and 90% relative humidity. A 4 µL droplet of the sample solution was deposited on a lacey formvar carbon-coated grid (Ted Pella, Redding, CA, USA) and was blotted with filter paper to remove excess fluid. The grid was then plunged into liquid ethane (around −183 °C) to ensure rapid vitrification of the sample in its native state. The specimens were then stored in liquid nitrogen (−196 °C) and, prior to imaging, transferred to the microscope using a cryo transfer tomography holder (Fischione, Export, PA, USA, Model 2550).
Samples were prepared using an automatic plunge freezer system (Leica EM GP, Wetzlar, Germany) with the environmental chamber set to 21 °C and 90% relative humidity. A 4 µL droplet of the sample solution was deposited on a lacey formvar carbon-coated grid (Ted Pella, Redding, CA, USA) and was blotted with filter paper to remove excess fluid. The grid was then plunged into liquid ethane (around −183 °C) to ensure rapid vitrification of the sample in its native state. The specimens were then stored in liquid nitrogen (−196 °C) and, prior to imaging, transferred to the microscope using a cryo transfer tomography holder (Fischione, Export, PA, USA, Model 2550).