Molecular Mechanism Of Binding Between Novel Human Coronavirus MERS-CoV And Its Receptor

Coronavirus are a pathogen of widespread and significant potential threat to people and livestock. Coronavirus has a broad tissue tropism,having the largest virus genome in RNA virus (about30kb). MERS-CoV (Middle East respiratory syndrome coronavirus) which appeared in September2012in the Middle East, can cause serious lung disease in human, the clinical manifestations of acute respiratory distress syndrome and associated with multiple organ failure, is the second largest high-pathogenic coronavirus following the SARS-CoV. The virus has been confirmed since September2012,as of8May this year,a total of536laboratory confirmed cases, and mortality rate as high as30.7%. Thus MERS-CoV has become a new coronavirus having a serious threat to human health and life safety.Coronaviruses are divided into four genus by ICTV (The International Committee on Taxonomy of Viruses):α, β,γ, and8coronavirus. β coronavirus has four branches (A-D). MERS-CoV and SARS-CoV is only less than50%amino acid identity in the more conservative DNA replication enzyme sequence, but have more than90%identical with HKU4and HKU5by comparing the MERS-CoV and other β coronavirus gene sequences. Therefore, MERS-CoV is classified as a new species of genus coronavirus C β branch, which is the first kind of disease infecting humans in C branch β coronavirus, SARS-CoV belongs to the coronavirus genus β B branch.Spike glycoprotein (S) is involved in receptor binding, membrane fusion and virus host cell invasion on the coronavirus surface and is the major target of neutralizing antibodies in the host. Subunits S1is responsible for receptor recognition and subunits S2start viral membrane fusion with the host. S1comprises two separate areas, N-terninal domain (NTD) and C-terminal region (CTD), these two parts can be used as receptor binding domain (RBD). S protein is closely related with its high pathogenicity, and also is one of the decisive factors of the host range. S protein can recognize a number of cell surface protein and glycolipids, such as hydroxyalky1,5-N-acetylneuraminic acid and5-N-acetylneuraminic acid which can be used as receptors or co-receptors of the α,γ CoV. Currently there are three types of enzyme protein was identified as a host coronavirus receptors, including angiotensin-converting enzyme2(ACE2) as SARS-CoV and human coronavirus HCoV-NL63receptor, mouse hepatitis coronavirus (MHV) uses cancer carcinoembryonic antigen-related cell adhesion molecule (CEACAM) as a receptor,aminopeptidase N (APN) as porcine respiratory coronavirus PRCV receptor. Interaction patterns of these receptors and viral S protein have been elaborated.We first used the mammalian expressed MERS-CoV S protein subunits S1,N-terminal domain (NTD) and C-terminal domain of Fc fusion protein. We therefore tested individually the binding of MERS-CoV S1and its N-and C-terminal-domain proteins to cell-surface-expressed CD26molecules. The receptor-binding capacity was attributed to the C-terminal amino acids367-606of MERS-CoV S1. We hereby referred to this domain as RBD. The potent interaction between MERS-CoV RBD and CD26was further demonstrated by surface Plasmon resonance assays, in which CD26binds to MERS-CoV RBD with a dissociation constant (KD) of about16.7nM, but does not bind to the RBD of SARS-CoV. We crystallized MERS-CoV RBD and solved its structure at a resolution of2.5A. We therefore divided the MERS-CoV RBD structure into two subdomains:a core and an external β-sheet.The study revealed clear structural homology between MERS-CoV RBD and SARS-CoV RBD. As the ADA-CD26interaction is shown to induce co-stimulatory signals in T cell, this may indicate a possible manipulation of the host immune system by MERS-CoV through competition for the ADA recognition site.In the study, we also expressed the NTD region MERS-CoV and SARS-CoV. we just made preliminary exploration for structure and function of MERS-CoV NTD and SARS-CoV NTD in the present study.Virus specific receptor is a valid target in the treatment of viral diseases:any virus require the corresponding receptors when invade the host cell and these receptors largely determine this virus susceptibility and tissue tropism susceptibility. Therefore, after resolve the MERS-CoV receptor complex structure, they can use this as a structural basis for the development of related drugs to block the binding process, and achieve the purpose of prevention or treatment. The in-depth research to occurrence and pathogenesis of coronavirus can contribute to the development of suitable antiviral drugs and vaccines, and tracking coronavirus trends. These can lead to the establishment of good forecasting and early warning mechanisms for the prevention of SARS, MERS infectious diseases, thus has an important significance in the prevention of public health emergencies caused by coronavirus.