2.5. Negative stain electron microscopy

Negative stain grids were prepared and examined as previously described [20]. Briefly, in-house carbon-coated copper grids were glow-discharged (PELCO easiGlow, TedPella) for 30 s. 3 μl of sample at a concentration of ~20 μg/ml was then applied to the grid for 30 s and blotted before staining twice with 1% uranyl acetate (2× 30s). Micrographs were collected using a Tecnai F20 microscope fitted with a 4 k × 4 K CMOS camera, operating at 200 kV with a nominal magnification of 50,000×.