Is not the location of the spike protein, and function / receptors it attaches to completely new? And wasn't the Chinese researcher (who has gone incommunicado) at the Wuhan Institute of Virology studying gain of function on exactly those spike protein locations?
I'm not a biologist, but have been trying to read all I can on this since this started.
Nope. Here is an article from 2008 discussing how SARS-CoV-1 (SARS2003) enters human cells. Spike protein binds to ACE2 receptors; same as SARS-CoV-2. You only have but so many ways into a human cell and SARS-CoV-2 is quite similar to SARS-CoV-1 and MERS-CoV (MERS2012). Structurally, it's slightly different. But those differences are very minor, like the differences between the April 2020 SARS-CoV-2 and the P.1 (Brazil) variants.
"And wasn't the Chinese researcher (who has gone incommunicado) at the Wuhan Institute of Virology studying gain of function on exactly those spike protein locations?"
That one I can't answer because I haven't found a reliable source of information about what exactly what happening there. It's possible, sure. I just don't know for certain there and I don't like to speculate without a lot of verified background information available. It's China, so what information does leak out is rarely reliable. Their government is so devoted to secrecy that much of what you hear ends up being disinformation and lies fed to further their agenda. Never trust China or anything coming from there.