Hacker News Reader

Comment by mirimir | Hacker News Reader

Except that some sorts of life, such as some sprouting plants, do incorporate those "non-proteinogenic" amino acids into proteins.

Which then screw up animals that eat them. Because they, in turn, also incorporate them into proteins. And those tweaked proteins elicit immune responses, because they weren't present during immune system development. And some of that immune response cross reacts with the normal host proteins. So you get autoimmune disease.

View on HN

This turned out to be an incredibly interesting (and educational) diversion!

It seems these amino acids aren't typically incorporated, but rather appear to serve as defense (https://www.ncbi.nlm.nih.gov/pubmed/21529857) and signaling molecules (https://www.ncbi.nlm.nih.gov/pubmed/28218981). Apparently humans do that sometimes as well (https://www.ncbi.nlm.nih.gov/pubmed/18828673). Sometimes the insects even end up using the toxic compound (in the linked example the non-protein amino acid L-DOPA) for their own purposes (https://www.ncbi.nlm.nih.gov/pubmed/27006098), which I find quite amusing.

More than just being eaten, apparently L-DOPA is released into the environment at an impressive rate in some cases (https://www.ncbi.nlm.nih.gov/pubmed/24598311).

Yes, I was wrong about that. Alfalfa seeds and sprouts don't themselves use canavanine in their proteins. And yes, plants do seriously get into chemical warfare.

While somewhat true, essentially the question of 20 amino acids still holds and trying to answer it is still meaningful (and in the same way article addresses it). Consider this: how old are these plant insecticides (or whatever they are)? Maybe some 150 mln years old? (I'm only assuming, of course, but it seems like a plausible assumption.) Well, the life on Earth itself is about 3.5 bln years old, and as far as we know it mostly utilizes the same set of 20 proteinogenic amino acids it did back then. It is only natural that given time, constantly mutating and evolving organisms would eventually learn to produce whatever amino acids possible, if it is useful (and being insecticide is obviously useful, if you are a plant, and for reasons you mention yourself it is natural to use as insecticide some compound that is not normally utilized in the other organism). The question is how did it occur that these amino acids weren't present during immune system development? Why it was always the same 20?

Yup and those shared articles don’t make a good counterargument or point..They are off topic. A better article(s) would have addressed the point of the number of amino acids...

Are you talking about human autoimmune disease? If so, do you have an examples and/or links to papers? I've read a lot about autoimmune diseases, and this hypothesis is not something I've ever heard of.

Edit: I see your earlier comment has some links. Thanks.

Yeah, some sprouts are ~dangerous. That is, if you're unlucky to have an immune system that got self-deselected in the "wrong" way.

That makes lots of sense. Do you have any examples of sprouting plants that so this? I'm guessing ones we consider poisonous?

woah that sounds interesting. Do you have some links to videos or articles which talk more about this?

Reply on news.ycombinator.com