Innate immunity to bacteria involves sensing of pathogens by pattern recognition molecules, such as Toll-like receptors. Toll proteins are mainly expressed at the plasma membrane of epithelial cells, but recently it has been proposed that the Nod molecules could represent a new group of recognition molecules that sense bacterial products within the cytoplasmic compartment. However, it has been unclear which bacterial products Nod proteins detect. In the June 6 Science, Stephen E. Girardin and colleagues from the Institut Pasteur show that Nod1 detects a unique muropeptide from gram-negative bacterial peptidoglycan (Science, 300:1584-1587, June 6, 2003).

Girardin et al. analyzed muropeptides from Neisseria meningitidis by reversed-phase high-performance liquid chromatography. They observed that human Nod1 specifically detects a unique diaminopimelate-containing N-acetylglucosamine, N-acetylmuramic acid (GlcNAc-MurNAc) tripeptide motif found in gram-negative bacterial peptidoglycan, resulting in activation of the transcription factor NF-κB pathway. In addition, they showed that in epithelial cells Nod1 is...

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