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Structure of PGN. (a) Common primary structure of PGN. (b) Variations in the peptide chain of PGN. Residues in parentheses may replace corresponding amino acids. The α-carboxylic acid of iso-d-Glu may be modified by an amide, Gly, or d-Ser. Dab, 2,4-diaminobutyric acid; DAHP, 2,6-diamino-3-hydroxypimelic acid; Hyg, threo-3-hydroxyglutamic acid; Hyl, hydroxylysine; Lan, lanthionine; Orn, ornithine.
