Hi,
I have no experience with biological databases and have no clue how I can find proteins that use for example only four amino aicds. I do research on genetic code evolution and just want to know what proteins could have been produced with only a small number of amino acids given. It would be perfect if I could get all proteins using four (or any other number) amino acids but if this isn't possible I would be happy about an explanation how I could get proteins using a specified set of amino acids (for example Lys, Pro, Ala, Ile).
Thanks in advance.
There's probably no 'clever' way of doing this other than taking a dataset of proteins, calculating AA compositions, and then just filtering out after the fact, but its pretty brute force.
You might take a look at the answer in this (essentially the same) question:
Amino acid protein software