INVESTIGATION OF THE LIPOPROTEOME OF THE LYME DISEASE BACTERIUM BORRELIA BURGDORFERI

Abstract

The spirochete bacterium Borrelia burgdorferi is the causative agent of Lyme borreliosis, the top vector-borne disease in the United States. B. burgdorferi is transmitted by hard-bodied Ixodes ticks in an enzootic tick/vertebrate cycle, with human infection occurring in an accidental, “dead-end” fashion. Despite the estimated 300,000 cases that occur each year, no FDA-approved vaccine is available for the prevention of Lyme borreliosis in humans. Development of new prophylaxes is constrained by the limited understanding of the pathobiology of B. burgdorferi, as past investigations have focused intensely on just a handful of identified proteins that play key roles in the tick/vertebrate infection cycle. As such, identification of novel B. burgdorferi virulence factors is needed in order to expedite the discovery of new anti-Lyme therapeutics. The multitude of lipoproteins expressed by the spirochete fall into one such category of virulence factor that merits further study. These lipoproteins play diverse roles in the organism and localize to different membrane-peripheral cellular compartments. The overarching goal of the current study was to further define the structure-function of the B. burgdorferi cell envelope by comprehensively and conclusively defining the localization of the bacterium’s predicted lipoproteome, using an epitope-tagged lipoprotein expression library. The data show that the majority of B. burgdorferi lipoproteins are surface-exposed, and that the plasmids of B. burgdorferi are enriched in surface lipoprotein genes relative to the chromosome. The study also establishes and validates a high-throughput proteomics approach that can be used in future studies to assess localization of endogenously expressed untagged lipoproteins. Finally, an analysis of the lipoproteome using data mining and in silico fold recognition algorithms demonstrates potential roles for several uncharacterized lipoproteins and identifies new targets for vaccine development.