2006 study inserts furin cleavage site into SARS-CoV spike at the exact residue where SARS-CoV-2's PRRA(R) site is - and demonstrates enhanced cell-to-cell fusion.

Before explaining this 2006 study, it's better to start with the 2020 paper that first described the furin cleavage site unique to SARS-CoV-2:

Coutard et al. observed SARS-CoV-2 "has a specific furin-like cleavage site absent in lineage b CoV including SARS-CoV sequences." Figure 2 is great because it aligns SARS-CoV-2 (aka 2019-nCoV) to not only SARS but also MERS and other CoVs with a known FCS marked with *.

Why is the FCS at the S1/S2 junction in the spike so important? A body of studies have shown that such a site can impact cell-to-cell fusion as well as the virus' ability to infect different cell types. This has been recently demonstrated in SARS-CoV-2 as well.

For example, in MERS-CoV, the S1/S2 FCS allows it to infect human lung and intestine (cancer derived) cells; without the FCS, the virus can only infect kidney (cancer derived) cells. https://t.co/6hnaHsPlW0 and

Dominic Dwyer, a member of the WHO team, on whether the covid virus could've originated from a lab accident: “Now, whether we were shown everything? You can never know. The group wasn’t designed to go and do a forensic examination of lab

WHO team chatted w Wuhan scientists, voted if lab origins were likely. This doesn't count as an investigation into #laborigins I hope @WHO knows that. "you don't want to jump to a conclusion based on several hours of conversation with Chinese

Jesse Bloom, virologist @fredhutch "surprised to see some members of the team dismiss the accidental lab leak theory while seeming to suggest, without any specific evidence, the possibility that frozen food might have played a

I was also very surprised to hear this dismissal of #laborigins (in favor of #popsicleorigins) because when @mattwridley and I co-wrote this @WSJ article, we were told...
https://t.co/wXqfSWSDTX?

Was this team equipped with the correct expertise to investigate a lab leak origin of covid-19? Did they follow any protocol to investigate #laborigins properly and independently?

If they were not and did not, then how can they rule out lab origins now?

@who going to investigate Covid-19 originating from frozen foods rather than #laborigins because lab leak too unlikely based on what the Wuhan lab personnel told them.

Not too confident that this @who team has much insight to the lab leak hypothesis - the WIV’s SARS research was done at BL2 and BL3 all these years, not BL4. Team could benefit from a lab leak/biosecurity expert weighing in on their report.

So the team says the virus was spreading before the Huanan market but that intermediate host is still the most likely #originsofcovid I’m keen to see the evidence that points to an intermediate host. Also, no mention of pangolins now? #pangolinpapers

Full press conference 2 hours here - see everyone on the other side...

Thanks @WHO and also for endorsing the frozen food origins hypothesis. I imagine it’s raining bonuses in China now for reporters: “WHO will investigate how killer virus that caused the covid pandemic may have first arrived in Wuhan, China via imported frozen fish...” https://t.co/5uKwqNYHA3