Explanation of Furin Cleavage site referred to in the above video Viruses rely on the biochemical mechanisms of the host cell they invade to bind and fuse with the host cell membrane and replicate inside the cell. The fusion part of that cascade of events can involve the virus using host cell enzymes to cleave one or more of the virus’ proteins at specific sites to facilitate entry into the host cell. Those sites are often composed of relatively short sequences of chemically basic amino acids called polybasic cleavage sites. At the junction of the S1 and S2 protein subunits, COVID-19 has just such a polybasic cleavage site that uses the host cell enzyme furin, which is found in many human organ systems and known to be involved in the pathogenic processes of viruses, for example, HIV, Ebola and various strains of coronavirus. The presence of the furin polybasic cleavage site may explain clinical reports of COVID-19’s ability to infect a variety of organ systems. The furin polybasic cleavage site in COVID-19 can be roughly defined by the amino acid sequence SPRRARS, which is Serine-Proline-Arginine-Arginine-Alanine-Arginine-Serine, where the cleavage takes place at the R-S junction. Within that broader sequence, the minimum sequence for a furin cleavage site is R-X-X-R, where Arginine (R) occurs in the 3rd and 6th positions and positions 4 and 5 can be any amino acid, but activity of the furin cleavage site can be significantly enhanced with a basic amino acid like Arginine in the 4th position, as occurs in COVID-19. It is very important to note that the furin polybasic cleavage site in COVID-19 is unique and has not been found in any of the coronaviruses yet identified as close relatives.
Very interesting and good to listen to people who make sense. The only point which I differ from is their surprise that it transits more easily indoors than outdoors and that this 'trick' may have been part of its laboratory manipulation (if indeed that is what happened) - it is easy to see why a respiratory virus would transmit to other people who are closer and in an enclosed space and with no air movements to disperse the virus. New to me was the 'Furin Cleavage' and I am now going to read your explanation of it. Thanks.
This is very heavy going but boils down to the way in which the virus attaches itself to the host cell's membrane and then breaks through into the cell, Without the enzymes capable of doing this 'breaking' (cleavage) the membranes of the virus and of the host cell might not fuse correctly or may not cleave to allow the virus inside the host cell. This explains one reason why some pathogens infect only certain hosts - that the correct enzymes are not present to do the breaking down. Enzymes are the chemicals (catalysts) probably best known by most people as chemicals which aid the digestion of food by 'cleaving' (or breaking it down) into smaller units (e.g. sucrose to glucose) and in this case are cleaving proteins at amino acid links (proteins being a sequence of amino acids). Obviously as we breathe air in we will breathe in all the pathogens in that air, but many may fail because of this lack of the correct enzymes (as well as for other reasons). I read elsewhere "The furin cleavage site might have been acquired by recombination with another virus possessing that site." This comes back to a point I have made many times elsewhere on the Forum: The danger of this virus is not only that it might mutate (change some, even very small, part of its genetic sequence) but it might combine its nuclear material with that of another virus (the process called 'recombination') and become more deadly. This is not exclusive to the Covid virus but is a reason why the World needs to be on its toes for the future.
