Bacteria modify PG to increase resistance to lysozyme, and some modifications can affect downstream innate detection.

<p>To disrupt efficient lysozyme binding to PG (A), bacteria modify their PG via <i>N</i>-deacetylation of NAG (B), <i>O</i>-acetylation of NAM (C), and <i>N</i>-glycolylation of NAM (D). Bacteria that <i>N</i>-deacetylate NAM (E), add WTAs to NAM (F), highly crosslink their PG (G), or amidate D-glutamic acid (H) are also more resistant to lysozyme. NAM on PG fragments that are released by lysozyme are in a reduced form and can activate the pattern recognition receptors NOD1 (I) and NOD2 (J). In contrast, PG released by bacterial lytic transglycosylases occurs with the formation of a 1,6-anhydrobond on the NAM residue, which can prevent NOD2 detection (K). <i>N</i>-deacetylation of NAM and <i>N</i>-glycolylation of NAM can decrease and increase NOD2-PG detection, respectively, whereas <i>O</i>-acetylation of NAM does not affect NOD2-PG detection. Abbreviations: NAG, <i>N</i>-acetylglucosamine; NAM, <i>N</i>-acetylmuramic acid; PG, peptidoglycan; WTAs, wall teichoic acids.