[subungual]

So denaturing a protein generally involves interfering with the noncovalent interactions (e.g. hydrogen bonds, attractions between internal charges) that allow it to fold into the right functional shape. Often times, these proteins folded under conditions that carefully facilitated their coming out the right way, so simply removing the denaturing stimulus (e.g. allowing them to cool) won't result in a reversion to their former configuration. This is what you see, for example, in cooking, where there's a discrete change that doesn't revert.

Prions are generally much more stable and can revert back to dangerous form once denaturing conditions change back. It takes a lot more to denature them irreversibly than it does most proteins. This stability is part of what makes them so dangerous and difficult to remove.

[dwohnitmok]

> Prions are generally much more stable and can revert back to dangerous form once denaturing conditions change back.

Indeed I'd imagine that almost definitionally prions must be difficult to denature. Since they are non-living and therefore have no way of "seeking out food," durability is the only way they can compete for reproduction. That is they can only become infectious if their resistance to denaturing was sufficiently high to resist environmental damage until their next target comes around.

[subungual]

Yeah, your logic is pretty good here. Prions are a super interesting emergent phenomenon of a complex system. In a weird way, like cancer or viruses, they're just an inevitability of having enough of certain materials interacting for long enough time. Proteins misfold in just such a way that allows them to induce the same type of misfolding in other proteins, leading to propagation. It's less a definitional thing, and more a matter of the fact that something more stable will persist longer, encounter more opportunities to propagate and preserve its form. That said, surviving harsh environments isn't an entirely necessary condition, as not all prion generation requires transmission. Unfortunately, if you have the wrong gene(s) broken, you're at risk of just generating them yourself. That said, transmission is significant, and since it involves needing to be able to survive a harsh outside environment with no propagation between hosts, extreme durability is a definite boon, as you suggest.

[ben_w]

It’s unusual to discuss a non-living chemical in terms of reproductive fitness, but I guess the word fits…

[monoideism]

There is currently no consensus on what constitutes a living thing. Some include viruses, some not. Most do not include prions, but prions do feature many of living things (eg, they evolve, adapt to their environment, replicate, etc).