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.

Crystallization and structure determination. The monomeric MERS S-NTD was crystallized by the sitting-drop vapour diffusion method at 18°C with 1 ml protein solution mixed with 1 ml reservoir buffer. High-quality crystals of MERS S-NTD grew in buffer of 0.2 M Magnesium chloride hexahydrate, 0.1 M BIS-TRIS pH 5.5, 25% w/v Polyethylene glycol 3,350at a protein concentration of 15 mg ml À 1 . Derivative crystals were obtained by soaking MERS S-NTD crystals overnight in mother liquor containing 2 mM KAuCl4. The SARS S-NTD was also crystallized by the sitting-drop vapour diffusion method at 18°C. High-quality crystals grew in 1.3 M Na/K hydrogen phosphate (pH 7.0) at a protein concentration of 15 mg ml À 1 . Diffraction data were collected with cryoprotected (in a reservoir solution containing 20% [v/v] glycerol) crystals at the Shanghai Synchrotron Radiation Facility beamline BL17U. All the datasets were processed with HKL2,000 software 37 . The structure of MERS S-NTD was determined by the SAD method using Au derivative data set with SHELXD (ref. 38) and Phaser-ep (ref. 39) , while the structure of SARS S-NTD was determined by the molecular replacement method using cryo-EM structure. The atomic model was completed with Coot 40 and refined with phenix.refine in Phenix 41 , and the stereochemical quality of the final model was assessed with Molprobity 42 . Data collection, processing and refinement statistics are summarized in Supplementary Table 1 . The native data set was collected at 0.979 Å, while the derivative data set was collected at 1.039 Å.