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.