AmiA is a penicillin target enzyme with dual activity in the intracellular pathogen Chlamydia pneumoniae

Area of Science:

• Microbiology
• Cell Biology
• Bacterial Pathogenesis

Background:

• Chlamydiaceae lack a detectable cell wall but exhibit a penicillin-induced "chlamydial anomaly."
• Evidence suggests circular peptidoglycan-like structures in Chlamydiaceae, hinting at cell wall-related processes.
• The mechanism behind the chlamydial anomaly and potential cell wall involvement remains unclear.

Purpose of the Study:

• To investigate the role of cell wall precursor-processing enzymes in Chlamydiaceae.
• To elucidate the mechanism of the chlamydial anomaly.
• To characterize the function and substrate specificity of Chlamydia pneumoniae AmiA.

Main Methods:

• Characterization of Chlamydia pneumoniae AmiA enzyme activity.
• Complementation of an Escherichia coli amidase mutant with Chlamydia pneumoniae AmiA.
• Enzyme assays using lipid II as a substrate.
• Analysis of penicillin sensitivity and substrate specificity.
• Investigation of the role of chlamydial CPn0902 (NlpD homolog).

Main Results:

• Chlamydia pneumoniae AmiA functions as an amidase, separating daughter cells in an E. coli mutant.
• Chlamydial AmiA exhibits dual amidase and carboxypeptidase activity, using lipid II as a substrate.
• The carboxypeptidase activity is penicillin-sensitive and linked to a penicillin-binding protein motif.
• Chlamydial CPn0902 acts as a carboxypeptidase, differing from its E. coli NlpD activator role.
• Functional conservation of AmiA suggests roles in chlamydial cytokinesis and host interaction.

Conclusions:

• Chlamydial AmiA possesses unique dual amidase/carboxypeptidase activity on lipid II, explaining penicillin sensitivity.
• The carboxypeptidase function of AmiA and CPn0902 likely contributes to the chlamydial anomaly.
• These findings provide mechanistic insights into chlamydial cell division and potential host immune modulation.