Detection of peptidoglycans by NOD proteins

Mechanisms of innate immune defense are based on the recognition of invariant microbial molecular patterns by specific receptors, followed by the activation of signaling pathways and the expression of effector molecules that will defeat the invading microorganism. Two recent reports add to the growing list of these pattern-recognition receptors by showing that the intracellular nucleotide-binding oligomerization domain 1 (NOD1) protein recognizes a diaminopimelate-containing muropeptide, a cell-wall component of Gram-negative bacteria.