Addition of non protein amino acids

[Palaeoprot]

Currently O and U are hardcoded in the mass.rs file

Would it be possible to use the other non-assigned letters, vis.

B, J, X, Z

for non-biological amino acids.

These could be assigned specific masses in the .yaml file.

[lazear]

I don't see why we couldn't do this. We could set the base mass to 0 for each of these amino acids and allow users to specify their masses using the standard static/variable mod setup.

• Are are of these letters already used for a specific non-canonical AA?
• Do you have a couple example spectra/PSMs you could share so that they could be incorporated as a test case?