1:21 "SARS Covid 2 may also get in by fusing directly with the cell membrane" I never heard that before, I heard entry was only via receptors, particularly ACE2 (although tunneling nanotubes are under investigation as a possible route). So how and under what circumstances will it - and can it - bypass such receptors? When there are none expressed by target cells nearby? When the target cells are already weakened in some way?
Instead of endosomic entry, it uses TMPRSS2, a membrane protease, to cleave the spike on the celle surface after interaction with ACE2. It can then fuse with the membrane as it does in the endosome. The cells always need a compatible receptor for the virus to enter.
@@maximecote-chenette8564 Thanks, that helps. But in that case what causes spike cleavage after endosomic entry has occurred? See 1:14 "Cleavage at the spike protein triggers the viral and host membranes to fuse together". Presumably it isn't TMPRSS2 if that's only found on the outer membrane and can only act in conjunction with ACE2.
@@chrisg3030 it doesnt enter via an endosome in the case of cell surface fusion. Once the virus and cell membranes have fused together, the inside of the virus, that is the RNA and enzymes, are released into the cytoplasm directly. You can see it as a simpler way to enter the cell, one that bypasses the need for the endosome.
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How do u get to know that
1:21 "SARS Covid 2 may also get in by fusing directly with the cell membrane" I never heard that before, I heard entry was only via receptors, particularly ACE2 (although tunneling nanotubes are under investigation as a possible route). So how and under what circumstances will it - and can it - bypass such receptors? When there are none expressed by target cells nearby? When the target cells are already weakened in some way?
Instead of endosomic entry, it uses TMPRSS2, a membrane protease, to cleave the spike on the celle surface after interaction with ACE2. It can then fuse with the membrane as it does in the endosome. The cells always need a compatible receptor for the virus to enter.
@@maximecote-chenette8564 Thanks, that helps. But in that case what causes spike cleavage after endosomic entry has occurred? See 1:14 "Cleavage at the spike protein triggers the viral and host membranes to fuse together". Presumably it isn't TMPRSS2 if that's only found on the outer membrane and can only act in conjunction with ACE2.
@@chrisg3030 it doesnt enter via an endosome in the case of cell surface fusion. Once the virus and cell membranes have fused together, the inside of the virus, that is the RNA and enzymes, are released into the cytoplasm directly. You can see it as a simpler way to enter the cell, one that bypasses the need for the endosome.
So easy to explain, and some people still antivaxxers.