Comparative proteome analysis reveals pathogen specific outer membrane proteins of Leptospira

A comprehensive in silico analysis of putative outer membrane and secretory hydrolases from the pathogenic Leptospira: Possible implications in pathogenesis

Outer surface/membrane and virulent secretory proteins are primarily crucial for pathogenesis. Secreted and outer membrane hydrolases of many pathogens play an important role in attenuating the host immune system. Leptospira expresses many such proteins, and few have been characterized to display various roles, including host immune evasion. However, identification, classification, characterization, and elucidation of the possible role of Leptospira's outer membrane and secretory hydrolases have yet to be explored. In the present study, we used bioinformatics tools to predict exported proteins from the pathogenic Leptospira proteome. Moreover, we focused on secretory and outer membrane putative hydrolases from the exported proteins to generate a deeper understanding. Our analysis yielded four putative outer/secretory hydrolases, LIC_10995, LIC_11183, LIC_11463, and LIC_12988, containing α/β hydrolase fold and displayed similarity with lipase motif. Moreover, their conservation analysis of the predicted hydrolases across the spectrum of different Leptospira species showed high clustering with the pathogenic species. Outer membrane and secretory proteins with lipolytic activity may have a role in pathogenesis. This is the first bioinformatics analysis of secretory and outer membrane α/β hydrolases from leptospiral species. However, experimental studies are indeed required to unravel this possibility.

Enhancement of clinical signs in C3H/HeJ mice vaccinated with a highly immunogenic Leptospira methyl-accepting chemotaxis protein following challenge

Leptospirosis is the most widespread zoonosis and a life-threatening disease in humans and animals. Licensed killed whole-cell vaccines are available for animals; however, they do not offer heterologous protection, do not induce long-term protection, or prevent renal colonization. In this study, we characterized an immunogenic Leptospira methyl-accepting chemotaxis protein (MCP) identified through a reverse vaccinology approach, predicted its structure, and tested the protective efficacy of a recombinant MCP fragment in the C3H/HeJ mice model. The predicted structure of the full-length MCP revealed an architecture typical for topology class I MCPs. A single dose of MCP vaccine elicited a significant IgG antibody response in immunized mice compared to controls (P < 0.0001), especially the IgG1 and IgG2a subclasses. The vaccination with MCP, despite eliciting a robust immune response, did not protect mice from disease and renal colonization. However, survival curves significantly differed between groups, and the MCP-vaccinated group developed clinical signs faster than the control group. There were differences in gross and histopathological changes between the MCP-vaccinated and control groups. The factors leading to enhanced disease process in vaccinated animals need further investigation. We speculate that anti-MCP antibodies may block the MCP signaling cascade and may limit chemotaxis, preventing Leptospira from reaching its destination, but facilitating its maintenance and replication in the blood stream. Such a phenomenon may exist in endemic areas where humans are highly exposed to Leptospira antigens, and the presence of antibodies might lead to disease enhancement. The role of this protein in Leptospira pathogenesis should be further evaluated to comprehend the lack of protection and potential exacerbation of the disease process. The absence of immune correlates of protection from Leptospira infection is still a major limitation of this field and efforts to gather this knowledge are needed.

Leptospiral protein LIC11334 display an immunogenic peptide KNSMP01

Leptospirosis is considered as a neglected tropical disease which is caused by pathogenic Leptospira spp. The precise mechanisms of leptospirosis pathogenesis are unclear and hence, the progress in development of treatment modalities has been dismal. The present study aimed to identify novel virulent factors of leptospires to understand the disease pathogenesis and to develop treatment modalities. Leptospira interrogans contains two chromosomes and encodes for ~3703 genes, but the functions of several open reading frames have not yet been explored. Among them, novel virulent associated leptospiral proteins (LIC11334, LIC11542, LIC11436, LIC11120 and LIC12539) were identified using VirulentPredict and the antigenicity of these targets was explored by VaxiJen server. Domain architecture of the pathogen specific proteins revealed that LIC11334 had potential to evoke significant immune response against leptospiral infection and LIC11436 contains four folds of immunoglobulin-like domain and plays a vital role in pathogenesis. Therefore, B-cell epitopes were predicted and the epitope of high virulence (and VaxiJen score from LIC11334) was chemically synthesized as peptide (KNSMP01) and labeled with Biotin (Biotin-SGSGEVENPDPKVAQEC). Binding affinity of KNSMP01 with MHC molecules was predicted and the molecule was discovered to have potential to elicit both humoral and cell mediated immune responses and found to interact with host components via hydrophobic interaction, hydrogen bonding and salt bridges. Rabbit antisera was raised against KNSMP01 and found to elicit antigenicity using Western, ELISA and dot blot assays. In silico and in vitro experiments show KNSMP01 to be a promising immunogen and may be a better vaccine candidate for leptospirosis.

Comparative proteome analysis reveals pathogen specific outer membrane proteins of Leptospira

Proteomes of pathogenic Leptospira interrogans and L. borgpetersenii and the saprophytic L. biflexa were filtered through computational tools to identify Outer Membrane Proteins (OMPs) that satisfy the required biophysical parameters for their presence on the outer membrane. A total of 133, 130, and 144 OMPs were identified in L. interrogans, L. borgpetersenii, and L. biflexa, respectively, which forms approximately 4% of proteomes. A holistic analysis of transporting and pathogenic characteristics of OMPs together with Clusters of Orthologous Groups (COGs) among the OMPs and their distribution across 3 species was made and put forward a set of 21 candidate OMPs specific to pathogenic leptospires. It is also found that proteins homologous to the candidate OMPs were also present in other pathogenic species of leptospires. Six OMPs from L. interrogans and 2 from L. borgpetersenii observed to have similar COGs while those were not found in any intermediate or saprophytic forms. These OMPs appears to have role in infection and pathogenesis and useful for anti-leptospiral strategies.