Characterization of Two Novel Lipopolysaccharide Phosphoethanolamine Transferases in Pasteurella multocida and Their Role in Resistance to Cathelicidin-2.

The lipopolysaccharide (LPS) produced by the Gram-negative bacterial pathogen has phosphoethanolamine (PEtn) residues attached to lipid A, 3-deoxy-d-manno-octulosonic acid (Kdo), heptose, and galactose. In this report, we show that PEtn is transferred to lipid A by the EptA homologue, PetL, and is transferred to galactose by a novel PEtn transferase that is unique to called PetG. Transcriptomic analyses indicated that expression was positively regulated by the global regulator Fis and negatively regulated by an Hfq-dependent small RNA. Importantly, we have identified a novel PEtn transferase called PetK that is responsible for PEtn addition to the single Kdo molecule (Kdo), directly linked to lipid A in the glycoform A LPS. assays showed that the presence of a functional and , and therefore the presence of PEtn on lipid A and Kdo, was essential for resistance to the cationic, antimicrobial peptide cathelicidin-2. The importance of PEtn on Kdo and the identification of the transferase responsible for this addition have not previously been shown. Phylogenetic analysis revealed that PetK is the first representative of a new family of predicted PEtn transferases. The PetK family consists of uncharacterized proteins from a range of Gram-negative bacteria that produce LPS glycoforms with only one Kdo molecule, including pathogenic species within the genera , , and We predict that many of these bacteria will require the addition of PEtn to Kdo for maximum protection against host antimicrobial peptides.