Lyme disease has become a worldwide public health problem and is now the most common tick-borne infection in the United States and Europe. To better understand how Borrelia burgdorferi, the causative agent of Lyme disease, persists in the infected tick and mammal, many laboratories have focused on identifying and characterizing outer surface proteins from this spirochete. The interface between B. burgdorferi and its tick or mammalian host is its outer surface; therefore, outer membrane proteins (OMPs) localized to the surface of this organism play an important role in virulence and disease. Along these lines, in the last funding period we focused on characterizing the outer membrane protein system that exports OMPs to the surface of B. burgdorferi. This OMP export complex, termed the ?-barrel assembly machine (BAM), is comprised of three major outer membrane proteins in B. burgdorferi, the OMP BamA along with two accessory lipoproteins, BamB and BamD. A second OMP transport system has recently been identified in some dual-membraned bacteria (i.e., bacteria with both an inner membrane and an outer membrane), which has been named the translocation and assembly module (TAM) system. The TAM system consists of the OMP designated TamA and a single inner membrane (IM) protein designated TamB. While the BAM system exports the majority of OMPs, the TAM system is now known to export various autotransporters and other virulence-associated OMPs. During our studies characterizing the borrelial BAM export complex, we also identified a hypothetical borrelial protein, BB0794, which we determined is a borrelial TamB ortholog. Interestingly, almost all dual-membraned organisms characterized to date have been found to encode a TamB ortholog, but only the Proteobacteria contain the complete TAM system comprised of both TamA and TamB. The functional role of TamB in all dual-membraned organisms lacking TamA, including B. burgdorferi, has therefore remained an unanswered question. Our recent studies, however, may have finally answered this question as we discovered that the borrelial TamB protein specifically interacts with BamA of the BAM complex. Consistent with TamB being involved in OMP export and outer membrane biogenesis, we observed that a TamB mutant has altered cellular morphology and increased sensitivity to antibiotics. The combined findings lead us to propose a new functional role for TamB orthologs in dual-membraned organisms, such as spirochetes. The underlying hypothesis of our proposed studies is that a better understanding of the OMP export systems in B. burgdorferi will lead to the identification of novel virulence factors and vaccine candidates for Lyme disease. Importantly, the studies we propose in this application could also change the current paradigm of OMP export and outer membrane biogenesis in many bacterial pathogens.

Public Health Relevance

Our long-term goal is to characterize the Borrelia burgdorferi outer surface protein export system. A better understanding of this process will allow us to identify novel virulence factors, possible Lyme disease vaccine candidates, and/or disease modulating therapeutics for Lyme disease. Given that the outer membrane protein export machine in B. burgdorferi is conserved, at some level, among all proteobacteria, our studies could also greatly benefit public health worldwide by helping to identify broad-spectrum antibacterials that could be used to treat many different devastating and serious diseases in the United States and abroad.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Bacterial Pathogenesis Study Section (BACP)
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Ilias, Maliha R
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University of Oklahoma Health Sciences Center
Schools of Medicine
Oklahoma City
United States
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Iqbal, Henna; Akins, Darrin R; Kenedy, Melisha R (2018) Co-immunoprecipitation for Identifying Protein-Protein Interactions in Borrelia burgdorferi. Methods Mol Biol 1690:47-55
Shrestha, Binu; Kenedy, Melisha R; Akins, Darrin R (2017) Outer Membrane Proteins BB0405 and BB0406 Are Immunogenic, but Only BB0405 Is Required for Borrelia burgdorferi Infection. Infect Immun 85:
Iqbal, Henna; Kenedy, Melisha R; Lybecker, Meghan et al. (2016) The TamB ortholog of Borrelia burgdorferi interacts with the ?-barrel assembly machine (BAM) complex protein BamA. Mol Microbiol 102:757-774
Kenedy, Melisha R; Scott 2nd, Edgar J; Shrestha, Binu et al. (2016) Consensus computational network analysis for identifying candidate outer membrane proteins from Borrelia spirochetes. BMC Microbiol 16:141
Dunn, Joshua P; Kenedy, Melisha R; Iqbal, Henna et al. (2015) Characterization of the ?-barrel assembly machine accessory lipoproteins from Borrelia burgdorferi. BMC Microbiol 15:70
Kenedy, Melisha R; Luthra, Amit; Anand, Arvind et al. (2014) Structural modeling and physicochemical characterization provide evidence that P66 forms a ?-barrel in the Borrelia burgdorferi outer membrane. J Bacteriol 196:859-72
Lenhart, Tiffany R; Kenedy, Melisha R; Yang, Xiuli et al. (2012) BB0324 and BB0028 are constituents of the Borrelia burgdorferi ?-barrel assembly machine (BAM) complex. BMC Microbiol 12:60
Kenedy, Melisha R; Lenhart, Tiffany R; Akins, Darrin R (2012) The role of Borrelia burgdorferi outer surface proteins. FEMS Immunol Med Microbiol 66:1-19
Kenedy, Melisha R; Akins, Darrin R (2011) The OspE-related proteins inhibit complement deposition and enhance serum resistance of Borrelia burgdorferi, the lyme disease spirochete. Infect Immun 79:1451-7
Caimano, Melissa J; Kenedy, Melisha R; Kairu, Toru et al. (2011) The hybrid histidine kinase Hk1 is part of a two-component system that is essential for survival of Borrelia burgdorferi in feeding Ixodes scapularis ticks. Infect Immun 79:3117-30

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