|WITCHELL, TIMOTHY - University Of Victoria|
|ESHGHI, AZAD - University Of Victoria|
|HOF, REBECCA - University Of Victoria|
|BOULANGER, MARTIN - University Of Victoria|
|WUNDER, ELSIO - Yale University|
|KO, ALBERT - Yale University|
|HAAKE, DAVID - University Of California|
|CAMERON, CAROLINE - University Of Victoria|
Submitted to: PLOS Neglected Tropical Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2014
Publication Date: 10/30/2014
Citation: Witchell, T.D., Eshghi, A., Nally, J.E., Hof, R., Boulanger, M.J., Wunder, E.A., Ko, A.I., Haake, D.A., Cameron, C.E. 2014. Post-translational modification of LipL32 during Leptospira interrogans infection. PLOS Neglected Tropical Diseases. 8(10):e32880. DOI: 10.1371/journal.pntd.0003280.
Interpretive Summary: Leptospirosis is a global infectious disease of animals and humans caused by the bacterium Leptospira. Pathogenic species of Leptospira are excreted in urine from infected animals and can continue to survive in suitable environments before coming into contact with a new reservoir or accidental host. Thus, leptospires have an inherent ability to survive a wide range of conditions encountered in nature during disease transmission and within mammals. To date, the majority of studies designed to understand how Leptospira cause disease have focused on characterizing the bacterium that grows in artificial conditions in the laboratory. However, this approach has inherent limitations since gene and protein expression of leptospires cultivated in vitro is very different to that of leptospires causing disease in situ. In this study, leptospires were collected from urine of experimentally infected rats for the specific analysis of the highly expressed outer membrane protein LipL32. Results demonstrate that LipL32 was modified by leptospires during infection compared to the same protein expressed by leptospires cultivated in vitro. Further, results showed that the modified forms of LipL32 exhibited less reactivity with serum from leptospirosis patients compared to unmodified forms; this suggests that LipL32 modifications may alter protein recognition by the immune response. This study reports, for the first time, modification of a Leptospira protein during infection, and suggests these modifications may have a functional consequence that contributes to bacterial persistence during infection.
Technical Abstract: Leptospirosis, a re-emerging disease of global importance caused by pathogenic Leptospira spp., is considered the world’s most widespread zoonotic disease. Rats serve as asymptomatic carriers of pathogenic Leptospira and are critical for disease spread. In such reservoir hosts, leptospires colonize the kidney, are shed in the urine, persist in fresh water and gain access to a new mammalian host through breaches in the skin. Previous studies have provided evidence for post-translational modification (PTM) of leptospiral proteins. In the current study we used proteomic analyses to determine the presence of PTMs on the highly abundant leptospiral protein, LipL32, from rat urine-isolated L. interrogans serovar Copenhageni compared to in vitro-grown organisms. We observed either acetylation or tri-methylation of lysine residues within multiple LipL32 peptides, including peptides corresponding to regions of LipL32 previously identified as epitopes. Intriguingly, the PTMs were unique to the LipL32 peptides originating from in vivo relative to in vitro grown leptospires. The identity of each modified lysine residue was confirmed by fragmentation pattern analysis of the peptide mass spectra. A synthetic peptide containing an identified tri-methylated lysine, which corresponds to a previously identified LipL32 epitope, demonstrated significantly reduced immunoreactivity with serum collected from leptospirosis patients compared to the peptide version lacking the tri-methylation. Further, a subset of the identified PTMs are in close proximity to the established calcium-binding and putative collagen-binding sites that have been identified within LipL32. The exclusive detection of PTMs on lysine residues within LipL32 from in vivo-isolated L. interrogans implies that infection-generated modification of leptospiral proteins may have a biologically relevant function during the course of infection. Although definitive determination of the role of these PTMs must await further investigations, the reduced immune recognition of a modified LipL32 epitope suggests the intriguing possibility that LipL32 modification represents a novel mechanism of immune evasion within Leptospira.