PCA

PCM

Residue type	PCM type	Category	Position	UniProt PTM accession	Entries in PDB
GLN	Pyrrolidone carboxylic acid	Named protein modification	Amino-acid side chain and backbone (N-terminal)	PTM-0261	1431
GLU	Pyrrolidone carboxylic acid	Named protein modification	Amino-acid side chain and backbone (N-terminal)	PTM-0262	0

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PDB entries from 2026-08-19