| Summary: | Acinetobacter baumannii causes a wide range of nosocomial infections.
This pathogen is considered a threat to human health due to the increasingly frequent isolation of multidrug-resistant strains. There is a major gap in knowledge on
the infection biology of A. baumannii, and only a few virulence factors have been
characterized, including lipopolysaccharide. The lipid A expressed by A. baumannii is
hepta-acylated and contains 2-hydroxylaurate. The late acyltransferases controlling
the acylation of lipid A have been already characterized. Here, we report the characterization of A. baumannii LpxO, which encodes the enzyme responsible for the
2-hydroxylation of lipid A. By genetic methods and mass spectrometry, we demonstrate that LpxO catalyzes the 2-hydroxylation of the laurate transferred by A. baumannii LpxL. LpxO-dependent lipid A 2-hydroxylation protects A. baumannii from
polymyxin B, colistin, and human -defensin 3. LpxO contributes to the survival of A.
baumannii in human whole blood and is required for pathogen survival in the waxmoth Galleria mellonella. LpxO also protects Acinetobacter from G. mellonella antimicrobial peptides and limits their expression. Further demonstrating the importance
of LpxO-dependent modification in immune evasion, 2-hydroxylation of lipid A limits
the activation of the mitogen-activated protein kinase Jun N-terminal protein kinase
to attenuate inflammatory responses. In addition, LpxO-controlled lipid A modification mediates the production of the anti-inflammatory cytokine interleukin-10 (IL-10)
via the activation of the transcriptional factor CREB. IL-10 in turn limits the production of inflammatory cytokines following A. baumannii infection. Altogether, our
studies suggest that LpxO is a candidate for the development of anti-A. baumannii
drugs.
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