This glycan shield has several effects on the S protein folding, its processing by host cell proteases, immune evasion, and the elicitation of humoral immune response as well. In comparison with S2 monomers, S1 monomers are more decorated with N-linked glycans. The S protein gene encodes 22 N-linked glycan sequins per monomer resulting in 66 N-linked glycans in one S glycoprotein. S protein is coated with polysaccharides. However, the RBD is a highly mutable region thus, it is not an ideal target site for the development of broad-spectrum antiviral. It has been proposed that inhibition of the interaction between RBD and ACE-2 can be useful in the treatment of SARS-CoV-2 infection. Additionally, outside the RBM, there is a unique interaction between Lys417 residue in RBD, which forms salt-bridge interactions with Asp30 of ACE-2. Another feature is the involvement of multiple tyrosine amino acids residues including Tyr449, Tyr 489, and Tyr505 from the RBD that form hydrogen bonds. An important feature at the RBD and ACE-2 interface is the hydrophilic interactions network as there are 13 hydrogen bonds and 2 salt bridges.

Īnalysis of the RBD and ACE-2 interface revealed that there are 17 amino acids of RBD in contact with 20 amino acids of ACE-2. In the RBD, there are nine cysteine residues eight of them form four pairs of disulfide bonds and three of these pairs are in the core that help in β-sheet structure stabilization, while the remaining pair connects the loops in the RBM distal end. The aminopeptidase N region in ACE-2 is responsible for RBD binding. This extended loop is known as the receptor-binding motif (RBM), containing most of the amino acids of the RBD that form the interactions with the ACE-2 receptors. There is an extended loop located between β4 and β7, which contains short β5 and β6 strands and α4 and α5 helices and loops. It was revealed that the RBD of SARS-CoV-2 is made up of a core that is built of twisted five-stranded antiparallel β-sheet of β1, β2, β3, β4 and β7. At the apex of each S1 monomer, there is one RBD. It is a V-shaped ectotrimer subunit that accommodates one ACE-2 recognition motif per monomer for binding. These amino acids are organized into four domains: N-terminal domain (NTD), C-terminal domain (CTD), or the receptor-binding domain (RBD), and two subdomains (SD1 and SD2) (Fig. S1 is a distal subunit that is composed of 672 amino acids (14–685) residues. The total recovery rates are estimated to be ~ 98% with 2% death rates. At the time of writing and as per the global statistics, 188,332,972 M are currently confirmed cases, while serious COVID-19 conditions constitute 0.6%, and the remaining 99.4% are relatively mild. Due to the rapidly increased number of SARS-CoV-2 cases, it was declared by the WHO as a global pandemic. Unfortunately, asymptomatic patients can contribute to viral transmission. Severe cases that are reported with high-risk individuals include respiratory failure and systemic inflammation, which in turn, can lead to further tragic consequences including multi-organ damage. People infected with SARS-CoV-2 may experience mild to moderate flu-like symptoms such as fever, cough, diarrhea, and shortness of breath as the most common symptoms. The spike (S), envelope (E), membrane (M), and nucleocapsid (N) constitute the structural proteins of the virus. The virus is made up of several structural and non-structural proteins each responsible for a particular step in viral infectivity and transmission. It was initially transmitted from bats through an intermediate host to humans. This virus has emerged in China, particularly in Wuhan, where several severe pneumonia cases were detected in December 2019. The severe acute respiratory syndrome coronavirus referred to as SARS-CoV-2 is an enveloped virus possessing a positive-sense single-stranded RNA of approximately 30 Kb length.

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