NaxD is a deacetylase required for lipid A modification and Francisella pathogenesis

Abstract

Summary Modification of specific Gram-negative bacterial cell envelope components, such as capsule, O-antigen and lipid A, are often essential for the successful establishment of infection. Francisella species express lipid A molecules with unique characteristics involved in circumventing host defences, which significantly contribute to their virulence. In this study, we show that NaxD, a member of the highly conserved YdjC superfamily, is a deacetylase required for an important modification of the outer membrane component lipid A in Francisella. Mass spectrometry analysis revealed that NaxD is essential for the modification of a lipid A phosphate with galactosamine in Francisella novicida, a model organism for the study of highly virulent Francisella tularensis. Significantly, enzymatic assays confirmed that this protein is necessary for deacetylation of its substrate. In addition, NaxD was involved in resistance to the antimicrobial peptide polymyxin B and critical for replication in macrophages and in vivo virulence. Importantly, this protein is also required for lipid A modification in F. tularensis as well as Bordetella bronchiseptica. Since NaxD homologues are conserved among many Gram-negative pathogens, this work has broad implications for our understanding of host subversion mechanisms of other virulent bacteria.

Unique Structural Modifications Are Present in the Lipopolysaccharide from Colistin-Resistant Strains of Acinetobacter baumannii

“…This modification is also seen on the lipid A from Francisella novicida as published previously by our laboratory (25,27) and others in the Francisella field (42,43). In the setting of F. novicida, the enzyme FlmK adds a GalN and a mannose residue to the 1 and 4= positions of lipid A whereas the FlmF2 enzyme is responsible for the addition of the GalN residue.…”

Bacterial strategies of resistance to antimicrobial peptides

“…Prevention of electrostatic binding of AMPs to the Gram-negative cell surface is achieved by amine-containing molecules (amino sugars, phosphoethanolamine (PEA) or glycine), which increase the positive charge of the anionic LPS component lipid A. P. aeruginosa and S. typhimurium attach aminoarabinose to a phosphate group in lipid A [96,97]. Acinetobacter baumannii, Francisella novicida and Bordetella species modify lipid A phosphate with galactosamine or glucosamine [98][99][100][101]. Furthermore, Gram-negative bacteria use PEA to decrease the anionic properties of LPS.…”

Defensive remodeling: How bacterial surface properties and biofilm formation promote resistance to antimicrobial peptides

“…It was found later that in order for the galactosamine addition to occur, deacetylation of the lipid A needed to take place. This deacetylation is done by NaxD, and NaxD mutants were more susceptible to PmB compared to the parental strain [116 ].…”