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.