Dear Jared There are existing het groups in the PDB chemical component dictionary for
unknown amino acid pdbe.org/chem/UNK unknown RNA nucleotide pdbe.org/chem/N unknown DNA nucleotide pdbe.org/chem/DN unknown RNA purine base pdbe.org/chem/P5P unknown RNA pyrimidine base pdbe.org/chem/Y5P Regards John PDBe
