Abstract
BackgroundLeptospirosis, 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.Methodology/Principal FindingsPrevious 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.Conclusions/SignificanceThe 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.
Highlights
Pathogenic Leptospira spp. are the causative agents of leptospirosis, which is considered to be the world’s most widespread zoonotic disease [1,2,3,4]
A synthetic peptide derived from LipL32 that incorporated a tri-methylated lysine modification exhibited less reactivity with serum from leptospirosis patients compared to an unmodified version of the peptide, suggesting LipL32 modifications may alter protein recognition by the immune response
The underlying mechanisms by which pathogenic Leptospira spp. are able to persist within mammalian hosts are incompletely understood, we have put forward the hypothesis that post-translational incorporation of methyl groups in leptospiral outer membrane proteins (OMPs) may enhance bacterial survival by modifying proteins and their respective functional interactions within the host. In support of this we have previously reported the addition of O-methyl esters to selected glutamic acid residues within the leptospiral protein OmpL32 [17], and Cao et al have detected mono, di- and tri-methylations on proteins from L. interrogans serovar Lai, including the major leptospiral lipoprotein LipL32 [18]
Summary
Pathogenic Leptospira spp. are the causative agents of leptospirosis, which is considered to be the world’s most widespread zoonotic disease [1,2,3,4]. Mammalian hosts that are chronically infected with Leptospira contain the spirochetes within the renal tubules of the kidney. 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
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