Cryo-EM structures of MERS-CoV and SARS-CoV spike glycoproteins reveal the dynamic receptor binding domains

Yuan, Yuan; Cao, Duanfang; Zhang, Yanfang; Ma, Jun; Qi, Jianxun; Wang, Qihui; Lu, Guangwen; Wu, Ying; Yan, Jinghua; Shi, Yi; Zhang, Xinzheng; Gao, George F.

Cryo-electron microscopy data collection and processing. Purified S protein (3 ml) with a concentration of B0.4 mg ml À 1 for MERS-CoV S or B0.3 mg ml À 1 for SARS-CoV S was placed on a glow-discharged holy carbon grid (GIG, 1.0 mm hole size, 400 mesh). After 4 s blotting with filter paper, the grid was flash plunged in liquid ethane using an automatic plunge device (Leica EM GP) with 10°C temperature and 99% humidity. Cryo-EM single particle data collection was performed using a 300 kV Titan Krios microscope equipped with K2 camera. Using the super resolution mode, each image was exposed of 11 s at a calibrated magnification of 38461 and an electron dose rate of B8 e per pixel per s, resulting in a total dose of B50 e Å À 2 that was fractionated into 32 movie frames. The images were binned before data processing, yielding a final pixel size of 1.3 Å.