Molecular Basis Of Recognition Between Novel Human Coronavirus MERS-COV And Its Receptor

The newly emerged Middle East respiratory syndrome coronavirus (MERS-CoV)was firstly identified in humans in the Middle East in September,2012, and later inseveral other countries. MERS patientsusuallydevelop severe pulmonary illness and thefatality rate is high, which leads to global concern about the potential for a MERSpandemic.Dipeptidyl peptidase4(DPP4) is the cellular receptor of MERS-CoV. Thebindingbetween the MERS-CoV S protein and human DPP4mediates viral attachmentto host cells and then initiates infection throughmembrane fusion.We firstly identified the receptor-binding domain (RBD) on the viral S protein,which directly mediates the interaction with DPP4. We then solved the3.0resolutioncrystal structure of MERS-CoV RBD complexed with the extracellular domain ofhuman DPP4. Our results show that viral RBD is composed of a core subdomain and aunique receptor-binding subdomain. The receptor-binding subdomain interacts withDPP4β-propeller domain, instead of its intrinsicα/β hydrolase domain. MERS-CoVRBD and related SARS-CoV RBD have ahigh structural conservation in their coresubdomains, but anotably divergentin the receptor-binding subdomains.Using site specific mutation and other biochemical methods such as pull-downassay and Surface Plasmon Resonance（SPR）, several key residues in the MERS-CoVRBD and in DPP4protein were identified that are critical for viral binding to DPP4.Besides, wecollaborated with Professor Zhang Linqi, developed and utilized apseudotyped virus system for studying MERS-CoV S protein-mediated infection. Withthe help of the pseudotyped virus system, key residues at the interface betweenMERS-CoV RBD and DPP4were additionally confirmed. Conservation of DPP4residues that contact the RBD of MERS-CoV among different mammals may hencehelp to track the animal source for MERS-CoV.Two RBD-specific potent human neutralizing monoclonal antibodies (MERS-4and MERS-27) were then isolatedfrom yeast-displayed single-chain variable regionfragments (scFvs) of nonimmune human antibody library in Zhang Linqi’s lab. To learnthe detailed neutralization mechanism of the two mAbs needs the fine-mapping of epitopes and Structural Biology may tell us a lot. We expressed, purified the twoantibodies and cutted both of them to generate Fabs. For both MERS4and MERS27, wegot the Fab-RBD complexes and subsequently obtained crystals. Future work would berequired to solve the crystal structures.The detailed structural information at the interface between MERS-CoV RBD andDPP4providesa more complete understanding of the viral attachment to host cells,which can guide development of therapeutics and vaccines against MERS-CoVinfection. Besides, RBDand RBD-specific neutralizing antibodies are both promisingcandidates for prophylactic and therapeutic interventions against MERS-CoV infection.