Figure 2
2019-n CoV cell cycle in host cells. The virus enters the target cells
through direct membrane fusion (A) or a clathrin-mediated endosomal
pathway (B). Binding of the surface unit of the S protein (S1) to
angiotensin-converting enzyme 2 (ACE2) facilitates the viral attachment.
Viral fusion is primed by TMPRSS2 and the active spike protein of
2019-nCoV acquire an RGD motif known to bind integrins. Spike
glycoprotein RGD lies in the receptor-binding domain. Binding to
integrin may play a supplemental role to ACE2 binding, like facilitating
endocytosis by signaling through the integrin. This motif is absent in
other coronaviruses. The viral RNA is unveiled by the effect of
endosomal cathepsins at low pH. Following, the replicase gene of the
viral genome is translated into large polyproteins which are cleaved by
the proteases to yield 16 non-structural proteins (nsps). In consequence
ofreplication, transcription and translation, viral nucleocapsids are
assembled with genomic RNA and N protein in the cytoplasm, followed by
budding into golgi intermediate compartment. Then, virions are released
from the infected cell through exocytosis.