Lipoprotein -terminal modification in : a new paradigm for extracellular acetylation and species-dependent Toll-like receptor 2 immunomodulation.

Lipoproteins are a defining feature of extracellular bacterial membrane surfaces. Acylation of an invariant -terminal cysteine residue tethers proteins to the cell surface, where they participate in many cellular processes occurring at the membrane-environment interface. Lipoproteins also double as key ligands for bacterial detection by the mammalian innate immune system, which when bound by Toll-like receptor 2 (TLR2) complexes orchestrate a pro-inflammatory response to clear infections. While nearly all bacteria synthesize lipoproteins, variable acylation states can attenuate TLR2 signaling. In , lipoproteins are -acetylated to form acetylated lipoproteins (Ac-LP) after being transported across the membrane. How high-energy acetyl donors are shuttled to the cell surface for trasnfer is unknown. Using a transposon-based genetic screen to identify mutants with altered TLR2 activation and reconstitution of the enzyme machinery, we now describe an acetylated heptaprenylglyceryl (Ac-HepG) carrier synthesized by PcrB/YvoF in the cytosol that is required for lipoprotein acetylation. We propose Ac-HepG is shuttled to the outer membrane leaflet for use by the previously uncharacterized integral membrane protein, ipoprotein eptaprenylglyceryl -cetyl ransferase (LhaT) (formerly YpjA), for -acetylation of the α-amino termini of lipoprotein substrates. We provide evidence that LhaT, which in most spp. makes the high-affinity Ac-LP TLR2 ligand, has become pseudogenized in the group subclade that harbors opportunistic pathogens. A naturally occurring poly-tyrosine insertion within LhaT from isolates prevents acetyl transfer, allowing the flanking lipoprotein remodeling gene to quantitatively convert the population to the TLR2-silent lyso-lipoprotein (lyso-LP) chemotype.IMPORTANCEProtein acetylation is an important and widespread post-translational modification. Annotation of LhaT and the lipoprotein -acetylation pathway provides a paradigm for how cells can source high-energy extracellular acetyl donors, with the enigmatic lipid Ac-HepG now joining the cytosolic acetyl-coenzyme A and acetyl-phosphate as acetyl group donors. While Ac-LP biosynthetic pathway genes appear to be universally conserved in all spp., those associated with pathogenic lineages have often lost function. In strains, LhaT has been inactivated by insertion of poly-tyrosine runs of variable length that favors chemotype conversion to lyso-LP and evasion of TLR2 detection. Lipoprotein chemotypes are thus critical determinants governing environmental and pathogen differentiation among spp.