Pyl Peptide is changed to wrong letter while we save one to Fasta or Sequence file

[NadezhdaPeskun]

Steps to Reproduce

1. Macro
2. Peptides >> Add Pyl
3. Save as Fasta and Sequence files

Actual behavior.
Pyl Peptide is shown as O letter while exporting to FASTA and Sequence.

Expected behavior
Pyl Peptide is shown as K letter while exporting to FASTA and Sequence.
As per @olganaz - Pyl belongs to K natural group so it should be represented as K letter in FASTA and Sequence
Please see comment from Olga below

Environment details:
Ketcher Version 2.20.0-rc.2 Build at 2024-03-27; 08:30:51
Indigo Toolkit Version 1.19.0-rc.2.0-g6c0e3fecf-x86_64-linux-gnu-11.2.1
Win10
Chrome Version 122.0.6261.129 (Official Build) (64-bit)

Related issues:

• Import and export fasta format for RNA, DNA and PEPTIDES Indigo#1755
• Autotests: Macro: UI for Open/Save As FASTA/Sequence #4280

[olganaz]

Various sources disagree on whether the symbol "O" is permissible in the FASTA format (https://en.wikipedia.org/wiki/FASTA_format VS https://zhanggroup.org/FASTA/). According to the IUPAC nomenclature, the symbol "O" is used to denote pyrrolysine. However, widely used tools by biologists such as BLAST and Uniprot generate an error when attempting to input an amino acid sequence containing the symbol "O". Therefore, it has been decided to support the import of the symbol "O", but when exporting, interpret it as the natural analog of pyrrolysine - "K" (lysine)