Lots of “gain of function” research going on everywhere. And synthetic biology is all the rage! It’s fun! It’s easy!
The emerging porcine epidemic diarrhea virus (PEDV) requires trypsin supplementation to activate its S protein for membrane fusion and virus propagation in cell culture. By substitution of a single amino acid in the S protein we created a recombinant PEDV (PEDV-S(FCS)) with an artificial furin protease cleavage site N-terminal of the putative fusion peptide. PEDV-S(FCS) exhibited trypsin-independent cell-cell fusion and was able to replicate in culture cells independent of trypsin, though to low titer.
Emphasis mine.
Adding furin cleavage sites is easy and undetectable, contrary to what some are saying.
https://www.researchgate.net/publica...try_and_Fusion