Wikipedia speaks of 500 naturally occurring amino acids. While most of them don’t get used by any life form for protein creation, there’s no fundamental reason why they can’t be.
This strikes me as a rather strong claim. If we take it as true wouldn’t we expect that some evidence exists for such use and if viable that the use of these amino acids would persist?
I take that you’re really saying we don’t know of any reasons they could not be used in life processes but the observations that they are not suggests that the inquiry should be along the lines of why not rather than assuming they could be but aren’t (at least from our current observations).
It’s not easy to evolve the usage of additional amino acids for use in proteins.
You need to synthesize the protein, you need to create a way for the amino acid to be incorporated into existing proteins (and if you just replace an existing three-letter code, you are going to mess up a lot of proteins) and you finally need to use the amino acid in a productive fashion.
If we look at why pyrrolysine exists in a few organisms with the last common ancestor 3 billion years ago, it’s mainly used for methyltransferase’s and by organisms which allows them to digest methylamine.
That leads to the thesis that it’s conserved in those organisms but not others that share the same common ancestors because it has a special use in them.
Most of the commonly used amino acids are simpler than pyrrolysine. From what I remember from my molecular biology lectures the professor did believe that more amino acids were used 3 billion years ago and that evolutionary pressure removed some complex amino acids from use.
This strikes me as a rather strong claim. If we take it as true wouldn’t we expect that some evidence exists for such use and if viable that the use of these amino acids would persist?
I take that you’re really saying we don’t know of any reasons they could not be used in life processes but the observations that they are not suggests that the inquiry should be along the lines of why not rather than assuming they could be but aren’t (at least from our current observations).
It’s not easy to evolve the usage of additional amino acids for use in proteins.
You need to synthesize the protein, you need to create a way for the amino acid to be incorporated into existing proteins (and if you just replace an existing three-letter code, you are going to mess up a lot of proteins) and you finally need to use the amino acid in a productive fashion.
If we look at why pyrrolysine exists in a few organisms with the last common ancestor 3 billion years ago, it’s mainly used for methyltransferase’s and by organisms which allows them to digest methylamine.
That leads to the thesis that it’s conserved in those organisms but not others that share the same common ancestors because it has a special use in them.
Most of the commonly used amino acids are simpler than pyrrolysine. From what I remember from my molecular biology lectures the professor did believe that more amino acids were used 3 billion years ago and that evolutionary pressure removed some complex amino acids from use.