8th April 2020 – It’s the spike protein on the virus – but how?
A Blog by Dr David J Flavell PhD FRCPath
Charity & Scientific Director of Leukaemia Busters
8th April 2020
What Makes COVID-19 So Very Contagious?
Strictly speaking viruses aren’t alive, they are little more than tiny packages of proteins, fat and genetic material that alone can do nothing; they use no energy, they need no food and they can’t reproduce themselves as free-living creatures, that is until they get inside one of our cells, then things change dramatically.
Viruses, like the current coronavirus that is the cause of COVID-19 only come alive after they’ve forced their way into one of our cells, then they swing into action by hijacking the molecular machinery of our own cell and use it to make millions of copies of themselves eventually filling up the interior of that cell to bursting point until the newly synthesised viruses are released.
Once released they move on in mass numbers to infect other cells in our nasal cavities, throat and lungs infecting more and more as the infection cycle continues. It’s only when our immune system kicks in producing neutralising antibodies and killer white blood cells that this cycle is finally arrested, the virus is eliminated and we get better.
But how does the virus get inside one of our cells in the first place?
Each and every one of our cells are surrounded by a membrane that acts as a barrier that is very particular about what it will and won’t let in. Viruses have evolved over hundreds of millions of years to develop cunning means to get through the membrane and into the interior of the cell they wish to hijack. The coronavirus that is causing us so much trouble presently has gone one step further by mutating in a way that has made it super-infectious – I’ll explain how.
The COVID-19 virus is covered over its surface with a protein that looks like an inverted spike which funnily enough is called the Spike or S Glycoprotein. It is the S protein that gives the virus the appearance of a crown or coronet also giving the name to the virus. The spike protein is absolutely instrumental to the virus gaining entry to the cell because it engages with and locks on to another protein called ACE-2 that is found on the surface of our own cells, in particular those in our noses, throats and lungs.
The viruses’ Spike protein and your own ACE-2 protein fit together much like a key fits a lock, it’s all down to the three dimensional shape of the two proteins, like a hand in a glove. The thing is that the spike protein of today’s troublesome coronavirus has undergone a mutation that has caused it to change its shape slightly so that it fits the “lock” of the ACE-2 protein on your own cells even better than before. That has had the effect of allowing the new coronavirus to attach to the outside of your cells ten times more strongly than before and it is this change that has made the virus super-infectious.
So what happens next once the virus has attached to your cell?
Your cell recognising that something, in this case the spike protein of the virus, has attached to its ACE-2 receptor is fooled into thinking that this is the usual natural thing that normally attaches to it and takes your own ACE-2 protein with the virus firmly attached inside the cell by a process called endocytosis.
It’s a kind of Trojan horse situation, the virus has fooled your cell into believing it is taking something natural and safe into its interior. By then it’s too late, the virus is inside and immediately springs into action to take over the molecular machinery of your own cell for its own nefarious purpose to reproduce, a process that eventually will destroy your cell after the nasty little virus has done its business and produced millions of copies of itself in the process.
The deed is done and millions of copies of the virus spill out from your damaged cell to continue to spread and infect other cells in your throat and lungs through exactly the same process.
Call in the cavalry!
The only thing that can bring a halt to the relentless and ruthless take-over of your own cells by the virus is your own immune system. In my blog tomorrow I’ll describe exactly how your immune system counter-attacks against the virus and why for 80% of infected individuals this allows them to recover from the illness whilst for around an unfortunate 20% it leads to worsening symptoms, life threatening pneumonia, lung damage and even death.
I’ll also be looking at some of the promising new possibilities already available that might prevent that from happening and dramatically change the course of events for patients who would otherwise die.