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Coronavirus: Mechanism of cell entry

So how does coronavirus gain entry into the human host cell ? There is an enzyme present on the membrane of the epithelial cells of alveoli in lungs, known as angiotensin converting enzyme - 2. It is similar to angiotensin converting enzyme i.e ACE enzyme which converts angiotensin 1 to angiotensin 2. However, this ACE-2 further degrades this angiotensin 2 and produces other form i.e angiotensin 1-7. The action of this are completely opposite to that of angiotensin 2. The coronavirus binds to this ACE-2 enzyme present on alveolar epithelial cells. Another protease enzyme named as TMPRSS2 present nearby cleaves a part of the S protein of coronavirus and kind of activates it. Because of this cleavage the envelope now fuses with the alveolar cell membrane and the virion is taken up inside the cell by a process known as endocytosis. The envelope the fuses with the membrane of the endosome releasing the RNA into the cytoplasm. The virus then uses host ribosomes and enzymes for translation RNA to proteins and also for replication of its RNA . Then the newly synthesised RNA and proteins assemble in Golgi apparatus taking a part of membrane also and release from the cell. So wherever this ACE-2 enzyme is present, coronavirus can gain entry into these cells. So this is responsible for tissue tropism of coronavirus i.e the organs which the coronavirus will be able to affect. Now, thats responseble for respiratory symptoms which occur in patients infected with coronavirus. This ACE-2 enzyme is also expressed in other tissues…these are small intestine epithelial cells which is responsible for GI symptoms in some patients… also in cardiac tissue.. then it is also expressed on liver thats why it is being speculated that why some patients may die of liver failure due to coronavirus. #coronavirus #covid-19 #physiologyopen