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

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

doi:10.1038/ncomms15092

Abstract

The envelope spike (S) proteins of MERS-CoV and SARS-CoV determine the virus host tropism and entry into host cells, and constitute a promising target for the development of prophylactics and therapeutics. Here, we present high-resolution structures of the trimeric MERS-CoV and SARS-CoV S proteins in its pre-fusion conformation by single particle cryo-electron microscopy. The overall structures resemble that from other coronaviruses including HKU1, MHV and NL63 reported recently, with the exception of the receptor binding domain (RBD). We captured two states of the RBD with receptor binding region either buried (lying state) or exposed (standing state), demonstrating an inherently flexible RBD readily recognized by the receptor. Further sequence conservation analysis of six human-infecting coronaviruses revealed that the fusion peptide, HR1 region and the central helix are potential targets for eliciting broadly neutralizing antibodies.

Highlights

The envelope spike (S) proteins of MERS-CoV and SARS-CoV determine the virus host tropism and entry into host cells, and constitute a promising target for the development of prophylactics and therapeutics
The cleaved form of the MERS-CoV S ectodomain was confirmed by SDS–polyacrylamide gel electrophoresis (SDS–PAGE), and further N-terminal sequencing revealed that the S ectodomain protein was cleaved after residue R748 (Supplementary Fig. 3), three residues ahead of the S2 cleavage site
Here we show that both MERS-CoV and SARS-CoV S trimers have flexible receptor binding domain (RBD), and we further constructed the receptor binding models for the MERS-CoV or SARS-CoV S trimers by superimposition of the S trimer structures with the RBD-receptor complex structures through the RBD domain (Fig. 5)

Summary

Introduction

The envelope spike (S) proteins of MERS-CoV and SARS-CoV determine the virus host tropism and entry into host cells, and constitute a promising target for the development of prophylactics and therapeutics. Peptide inhibitors have been designed targeting these HR regions and been proven to be effective in vitro and in vivo[18,19,22,23,24] These studies have provided insight into the characteristics of MERS-CoV and SARS-CoV S components; the overall S protein structures of these two highly pathogenic CoVs remain to be investigated. This will further enhance our understanding of S protein function and subsequent design of broadly neutralizing antibodies and vaccine immunogens. We present high-resolution structures of the trimeric MERS-CoV and SARS-CoV S proteins in its pre-fusion conformation by single particle cryo-electron microscopy (cryo-EM). We captured two states of the RBD that is facilitated to receptor binding and further analysis of S proteins revealed the potential targets for eliciting broadly neutralizing antibodies

Methods

Results

Conclusion