Pathophysiology of the virus:
SARS-CoV-2 has four structural proteins, which are ”S” for spike, ”E” for envelope, ”M” for membrane, and ”N” for nucleocapsid, which encapsulates single-stranded viral RNA ( Sanders et al., 2020). Spike protein is cleaved into S1 and S2 by the host cell protease, one of which is transmembrane protease serine-2 (TMPRSS2) which requires certain pH for being active. S1 subunit binds with the host cell surface receptors, while S2 subunit mediates membrane fusion (Sanders et al., 2020). Spike protein has a strong binding affinity to human ACE-2 receptors which expressed in the respiratory system and likely uses them as a mechanism for cell entry (Zhang et al., 2020a). Then the viral genetic material is released into the host cell, the genomic RNA of coronavirus acts as mRNA for translation of the replicase polyprotein 1a and 1ab (Zhang et al., 2020a). Afterwards, autoproteolytic cleavage of these polyproteins produces number of non-structural proteins including RNA-dependent RNA polymerase, helicase and nonstructural protein 3, 4, and 6. These nonstructural proteins are thought to be responsible for anchoring the coronavirus replication/transcription complex through recruitment of intracellular endoplasmic reticulum membranes to form double membrane vesicles (DMV). RNA-dependent RNA polymerase (RdRp) and helicase localize to DMV and drive the production of subgenomic RNAs from which the structural and accessory proteins are produced in the next phase of translation (Chen et al., 2020). Once synthesized, transmembrane structural proteins ”S”, ”M”, and ”E” are inserted, and folded in the ER and then transported to the endoplasmic reticulum–golgi intermediate compartment (ERGIC). The ”N” proteins on contrast bind the viral genomic RNA in cytoplasm to form nucleocapsid. After assembly, mature virions are released by exocytosis to infect another cell.