The S-Spike has 2 substructures labeled S1 and S2. You can think of S1 as the top and it has the “sticky” part called the Receptor Biding Domain (RBD) that binds to the ACE2 Receptor. The S2 is the structure that anchors the S-Spike to the ball. What makes SARS-CoV-2 so suspicious is the existence of a furin cleavage site between S1 and S2 that causes the S-Spike to spring open like a 3-jawed monster.
That furin cleavage site isn’t in any other beta-coronaviruses. In the tens of thousands of beta-coronaviruses researchers all over the world have sequences, I believe they’ve only found 1 other beta-coronavirus with an S-Spike furin cleavage site but even that was different from the SARS-CoV-2 furin cleavage site.
Where we go from suspicious to unbelievable is in how that furin cleavage site is contructed. It is done with 2 arginine amino acids sitting back-to-back in the sequence. Arginine can be encoded in RNA using the codons CGT, CGC, CGA, CGG, AGA, or AGG. Any of the 6 makes arginine, but coronaviruses have a natural bias into which codons are used for arginine and rarely use the CGG codon. SARS-CoV-2, in its furin cleavage site, has back-to-back double CGG codons. That has NEVER been seen before in any beta-coronavirus. I’m not saying just in a cleavage site, or in an S-Spike, but anywhere.
SARS-CoV-2 also seems to hate that double CGG codon because it keeps trying to evolve out of it. Variants with changes to that site are vastly over-represented when we shouldn’t see that at all because the furin cleavage site is what make the virus so infectious to human cells. Evolving out of either CGG typically ruins the furin cleavage site which effectively ends its ability to reproduce.
That double CGG-CGG arginine codon in the SARS-CoV-2 is what Nobel laureate and former President of CalTech David Baltimore called the “smoking gun”, and that is exactly what it is.
There are many other pieces that point to this virus coming out of the Wuhan Institute of Virology but if I have to point to a single piece of evidence making the case that this virus isn’t natural, it is the double CGG-CGG furin cleavage site.
If it is something else you wanted reference material to back something I’ve said, just let me know and I’ll be happy to provide links to reputable scientific sources (usually Nature, Science, Lancet, Wiley, or the NIH site).