Anything that'll denature a protein. Bleach can do it. Stronger acids and bases can do it. Heat can do it. Though on the latter, IIRC you are talking something in the 200+F range. Even with something like a big forest fire, you can get stuff that doesn't reach that temperature under leaf litter and stuff. I mean, protein is pretty stable absent a reactive environment. Otherwise, things like jerked meat would be nutritionally and calorically bunk after a few months.Fire seems to be the only way to kill the prions, but it there has been some concern recently that it can survive some.