Structural characterization of muropeptides fromChlamydia trachomatispeptidoglycan by mass spectrometry resolves ``chlamydial anomaly''

The existence of peptidoglycan (PG) in pathogenic Chlamydiae is supported by genetic data and antibiotic susceptibility, but the failure to isolate PG from pathogenic Chlamydiae has led to the "chlamydial anomaly." Moreover, the lack of a transglycosylase domain in some Chlamydia penicillin-binding proteins suggests that Chlamydiae may possess a "glycanless PG." We successfully enriched Chlamydia muropeptides from Chlamydia-infected cell lysates using nucleotide-binding oligomerization domain-containing protein 2 (NOD2)-dependent NF-κB activation as a biomarker for the presence of PG fragments in specific fractions. Mass spectrometry analysis indicated the presence of chlamydial muropeptides and classified chlamydial PG as type A1γ in the Schleifer and Kandler classification. This study disproves the glycanless PG hypothesis and is, to our knowledge, the first structural confirmation of chlamydial PG in pathogenic species.