The leptospiral LipL21 and LipL41 proteins exhibit a broad spectrum of interactions with host cell components

Cleavage of cell junction proteins as a host invasion strategy in leptospirosis

Infection and invasion are the prerequisites for developing the disease symptoms in a host. While the probable mechanism of host invasion and pathogenesis is known in many pathogens, very little information is available on Leptospira invasion/pathogenesis. For causing systemic infection Leptospira must transmigrate across epithelial barriers, which is the most critical and challenging step. Extracellular and membrane-bound proteases play a crucial role in the invasion process. An extensive search for the proteins experimentally proven to be involved in the invasion process through cell junction cleavage in other pathogens has resulted in identifying 26 proteins. The similarity searches on the Leptospira genome for counterparts of these 26 pathogenesis-related proteins identified at least 12 probable coding sequences. The proteins were either extracellular or membrane-bound with a proteolytic domain to cleave the cell junction proteins. This review will emphasize our current understanding of the pathogenic aspects of host cell junction-pathogenic protein interactions involved in the invasion process. Further, potential candidate proteins with cell junction cleavage properties that may be exploited in the diagnostic/therapeutic aspects of leptospirosis will also be discussed. KEY POINTS: • The review focussed on the cell junction cleavage proteins in bacterial pathogenesis • Cell junction disruptors from Leptospira genome are identified using bioinformatics • The review provides insights into the therapeutic/diagnostic interventions possible.

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.

Global proteome of the saprophytic strain Leptospira biflexa and comparative analysis with pathogenic strain Leptospira interrogans uncover new pathogenesis mechanisms

Leptospira is a genus of bacteria that includes free-living saprophytic species found in water or soil, and pathogenic species, which are the etiologic agents of leptospirosis. Besides all the efforts, there are only a few proteins described as virulence factors in the pathogenic strain L. interrogans. This work aims to perform L. biflexa serovar Patoc1 strain Paris global proteome and to compare with the proteome database of pathogenic L. interrogans serovar Copenhageni strain Fiocruz L1-130. We identified a total of 2327 expressed proteins of L. biflexa by mass spectrometry. Using the Get Homologues software with the global proteome of L. biflexa and L. interrogans, we found orthologous proteins classified into conserved, low conserved, and specific proteins. Comparative bioinformatic analyses were performed to understand the biological functions of the proteins, subcellular localization, the presence of signal peptide, structural domains, and motifs using public softwares. These results lead to the selection of 182 low conserved within the saprophyte, and 176 specific proteins of L. interrogans. It is anticipated that these findings will indicate further studies to uncover virulence factors in the pathogenic strain. This work presents for the first time the global proteome of saprophytic strain L. biflexa serovar Patoc, strain Patoc1. SIGNIFICANCE: The comparative analysis established an array of specific proteins in pathogenic strain that will narrow down the identification of immune protective proteins that will help fight leptospirosis.

Indi Dharmayanti NL, Astagiri Yusuf P. Production and characterization of immunoglobulin G anti-rLipL32 antibody as a biomarker for the diagnosis of leptospirosis

Background and Aim

Microscopic agglutination test (MAT) for the diagnosis of leptospirosis requires live cultures and is serovar-specific, while polymerase chain reaction (PCR) requires expensive equipment and sample preparation. The rLipL32 protein is conserved and can be used for the production of immunoglobulin G (IgG) anti-rLipL32 antibody, which can be used as a biomarker for leptospirosis diagnosis. This study aimed to produce and characterize an IgG anti-rLipL32 antibody as a biomarker for leptospirosis diagnosis.

Materials and Methods

Escherichia coli rLipL32 was cultured and analyzed by PCR and sequencing. Cultures were used for rLipL32 protein expression and purification and the rLipL32 protein was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The rLipL32 protein was used to produce anti-rLipL32 serum and was analyzed by enzyme-linked immunosorbent assay (ELISA). Serum was purified to obtain IgG anti-rLipL32 antibody and characterized by SDS-PAGE and western blotting.

Results

PCR was able to amplify the LipL32 gene from E. coli rLipL32, and sequencing analysis showed 99.19% similarity with pathogenic Leptospira. SDS-PAGE analysis showed a 32-kDa band. ELISA results showed an increase in OD in anti-rLipL32 serum compared to preimmune serum. Western blotting results showed that the IgG anti-rLipL32 antibody was able to bind and cross-reacts with pathogenic Leptospira serovar but not with E. coli or Staphylococcus aureus.

Conclusion

IgG anti-rLipL32 antibody has high specificity and sensitivity against Leptospira pathogens. These findings suggest that IgG anti-rLipL32 antibody is a promising biomarker for the diagnosis of leptospirosis.

Physiological Temperature and Osmotic Changes Drive Dynamic Proteome Alterations in the Leptospiral Outer Membrane and Enhance Protein Export Systems

Leptospirosis, a remerging zoonosis, has no effective vaccine or an unambiguous early diagnostic reagent. Proteins differentially expressed (DE) under pathogenic conditions will be useful candidates for antileptospiral measures. We employed a multipronged approach comprising high-resolution TMT-labeled LC-MS/MS-based proteome analysis coupled with bioinformatics on leptospiral proteins following Triton X-114 subcellular fractionation of leptospires treated under physiological temperature and osmolarity that mimic infection. Although there were significant changes in the DE proteins at the level of the entire cell, there were notable changes in proteins at the subcellular level, particularly on the outer membrane (OM), that show the significance of subcellular proteome analysis. The detergent-enriched proteins, representing outer membrane proteins (OMPs), exhibited a dynamic nature and upregulation under various physiological conditions. It was found that pathogenic proteins showed a higher proportion of upregulation compared to the nonpathogenic proteins in the OM. Further analysis identified 17 virulent proteins exclusively upregulated in the outer membrane during infection that could be useful for vaccine and diagnostic targets. The DE proteins may aid in metabolic adaptation and are enriched in pathways related to signal transduction and antibiotic biosynthesis. Many upregulated proteins belong to protein export systems such as SEC translocase, T2SSs, and T1SSs, indicating their sequential participation in protein transport to the outer leaflet of the OM. Further studies on OM-localized proteins may shed light on the pathogenesis of leptospirosis and serve as the basis for effective countermeasures.

Human leptospirosis: In search for a better vaccine

Leptospirosis is a neglected disease caused by bacteria of the genus Leptospira and is more prevalent in tropical and subtropical countries. This pathogen infects humans and other animals, responsible for the most widespread zoonosis in the world, estimated to be responsible for 60 000 deaths and 1 million cases per year. To date, commercial vaccines against human leptospirosis are available only in some countries such as Japan, China, Cuba and France. These vaccines prepared with inactivated Leptospira (bacterins) induce a short-term and serovar-specific immune response, with strong adverse side effects. To circumvent these limitations, several research groups are investigating new experimental vaccines in order to ensure that they are safe, efficient, and protect against several pathogenic Leptospira serovars, inducing sterilizing immunity. Most of these protocols use attenuated cultures, preparations after LPS removal, recombinant proteins or DNA from pathogenic Leptospira spp. The aim of this review was to highlight several promising vaccine candidates, considering their immunogenicity, presence in different pathogenic Leptospira serovars, their role in virulence or immune evasion and other factors.

Proteomic profile of naturally released extracellular vesicles secreted from Leptospira interrogans serovar Pomona in response to temperature and osmotic stresses

Bacterial extracellular vesicles (EVs) are generally formed by pinching off outer membrane leaflets while simultaneously releasing multiple active molecules into the external environment. In this study, we aimed to identify the protein cargo of leptospiral EVs released from intact leptospires grown under three different conditions: EMJH medium at 30 °C, temperature shifted to 37 °C, and physiologic osmolarity (EMJH medium with 120 mM NaCl). The naturally released EVs observed under transmission electron microscopy were spherical in shape with an approximate diameter of 80-100 nm. Quantitative proteomics and bioinformatic analysis indicated that the EVs were formed primarily from the outer membrane and the cytoplasm. The main functional COG categories of proteins carried in leptospiral EVs might be involved in cell growth, survival and adaptation, and pathogenicity. Relative to their abundance in EVs grown in EMJH medium at 30 °C, 39 and 69 proteins exhibited significant changes in response to the temperature shift and the osmotic change, respectively. During exposure to both stresses, Leptospira secreted several multifunctional proteins via EVs, while preserving certain virulence proteins within whole cells. Therefore, leptospiral EVs may serve as a decoy structure for host responses, whereas some virulence factors necessary for direct interaction with the host environment are reserved in leptospiral cells. This knowledge will be useful for understanding the pathogenesis of leptospirosis and developing as one of vaccine platforms against leptospirosis in the future.

Evaluation of Leptospira interrogans knockdown mutants for LipL32, LipL41, LipL21, and OmpL1 proteins

Introduction

Leptospirosis is a worldwide zoonosis caused by pathogenic and virulent species of the genus Leptospira, whose pathophysiology and virulence factors remain widely unexplored. Recently, the application of CRISPR interference (CRISPRi) has allowed the specific and rapid gene silencing of major leptospiral proteins, favoring the elucidation of their role in bacterial basic biology, host-pathogen interaction and virulence. Episomally expressed dead Cas9 from the Streptococcus pyogenes CRISPR/Cas system (dCas9) and single-guide RNA recognize and block transcription of the target gene by base pairing, dictated by the sequence contained in the 5' 20-nt sequence of the sgRNA.

Methods

In this work, we tailored plasmids for silencing the major proteins of L. interrogans serovar Copenhageni strain Fiocruz L1-130, namely LipL32, LipL41, LipL21 and OmpL1. Double- and triple-gene silencing by in tandem sgRNA cassettes were also achieved, despite plasmid instability.

Results

OmpL1 silencing resulted in a lethal phenotype, in both L. interrogans and saprophyte L. biflexa, suggesting its essential role in leptospiral biology. Mutants were confirmed and evaluated regarding interaction with host molecules, including extracellular matrix (ECM) and plasma components, and despite the dominant abundance of the studied proteins in the leptospiral membrane, protein silencing mostly resulted in unaltered interactions, either because they intrinsically display low affinity to the molecules assayed or by a compensation mechanism, where other proteins could be upregulated to fill the niche left by protein silencing, a feature previously described for the LipL32 mutant. Evaluation of the mutants in the hamster model confirms the augmented virulence of the LipL32 mutant, as hinted previously. The essential role of LipL21 in acute disease was demonstrated, since the LipL21 knockdown mutants were avirulent in the animal model, and even though mutants could still colonize the kidneys, they were found in markedly lower numbers in the animals' liver. Taking advantage of higher bacterial burden in LipL32 mutant-infected organs, protein silencing was demonstrated in vivo directly in leptospires present in organ homogenates.

Discussion

CRISPRi is now a well-established, attractive genetic tool that can be applied for exploring leptospiral virulence factors, leading to the rational for designing more effective subunit or even chimeric recombinant vaccines.

LIC12254 Is a Leptospiral Protein That Interacts with Integrins via the RGD Motif

Pathogenic leptospires can bind to receptors on mammalian cells such as cadherins and integrins. Leptospira effectively adheres to cells, overcomes host barriers and spreads into the bloodstream, reaching internal target organs such as the lungs, liver and kidneys. Several microorganisms produce proteins that act as ligands of integrins through the RGD motif. Here, we characterized a leptospiral RGD-containing protein encoded by the gene lic12254. In silico analysis of pathogenic, intermediate and saprophytic species showed that LIC12254 is highly conserved among pathogenic species, and is unique in presenting the RGD motif. The LIC12254-coding sequence is greatly expressed in the virulent Leptospira interrogans L1-130 strain compared with the culture-attenuated L. interrogans M20 strain. We also showed that the recombinant protein rLIC12254 binds to αVβ8 and α8 human integrins most likely via the RGD motif. These interactions are dose-dependent and saturable, a typical property of receptor-ligand interactions. The binding of the recombinant protein lacking this motif-rLIC12254 ΔRAA-to αVβ8 was almost totally abolished, while that with the α8 human integrin was decreased by 65%. Taken together, these results suggest that this putative outer membrane protein interacts with integrins via the RGD domain and may play a key role in leptospirosis pathogenesis.

Overcoming problems to produce the recombinant protein LipL21 of Leptospira interrogans

The production of leptospiral recombinant proteins in the soluble form and in high yield from Escherichia coli is still a challenge. This work presents the cloning, expression and purification of the outer membrane protein of Leptospira interrogans, LipL21, which is considered an interesting target for vaccine and diagnostics development. The expression profile and yield of LipL21 was compared after cloning in the vectors pAE, pET28a and pET-SUMO, and it was observed that LipL21 was expressed in a low amount with pAE vector. By using the pET-28a vector, protein expression was increased, but the majority of the product was obtained as inclusion bodies. As a highlight, using a pET-SUMO vector was shown to overcome the problems of low expression and solubility of the lipoprotein LipL21.

In Silico Approaches for the Identification of Aptamer Binding Interactions to Leptospira spp. Cell Surface Proteins

Aptamers are nucleic acids that can bind with high affinity and specificity to a range of target molecules. However, their functionality relies on their secondary and tertiary structures such that the combination of nucleotides determines their three-dimensional conformation. In this study, the binding mechanisms of candidate aptamers and their interactions with selected target proteins found in the cell surface of Leptospira were predicted to select high-affinity aptamers. Four aptamers were evaluated through molecular modeling and docking using available software and web-based tools, following the workflow previously designed for in silico evaluation of DNA aptamers. The most predominant and highly conserved surface-exposed proteins among pathogenic Leptospira species were used as aptamer targets. The highest number of interactions was seen in aptamers AP5 and AP1. Hydrogen bonds, along with a few hydrophobic interactions, occur in most aptamer-protein complexes. Further analysis revealed serine, threonine, glutamine, and lysine as main protein residues. H-bond interactions occur mostly with polar amino acids, as reflected in the predicted interaction profiles of aptamer-protein complexes. In silico strategies allowed the identification of key residues crucial in aptamer-target interaction during aptamer screening. Such information can be used in aptamer modification for improved binding affinity and accuracy for diagnostics application.

Host Cell Binding Mediated by Leptospira interrogans Adhesins

Leptospirosis is a neglected infectious disease with global impact on both humans and animals. The increase in urban development without sanitation planning is one of the main reasons for the disease spreading. The symptoms are similar to those of flu-like diseases, such as dengue, yellow fever, and malaria, which can result in a misleading clinical diagnosis. The characterization of host-pathogen interactions is important in the development of new vaccines, treatments, and diagnostics. However, the pathogenesis of leptospirosis is not well understood, and many gaps remain to be addressed. Here, we aimed to determine if Leptospira strains, virulent, culture-attenuated, and saprophytic, and the major outer membrane proteins OmpL37, OmpL1, LipL21, LipL41, and LipL46 are able to adhere to different endothelial, epithelial and fibroblast cell lines in vitro. We showed that virulent leptospires robustly bind to all cells compared to the culture-attenuated and saprophytic lines. The recombinant proteins exhibited certain adhesion, but only OmpL1 and LipL41 were able to bind to several cell lines, either in monolayer or in cell suspension. Blocking OmpL1 with polyclonal antibodies caused a decrease in bacterial binding to cells, contrasting with an increase observed when anti-LipL41 antibodies were used. The adhesion of OmpL1 to HMEC-1 and EA.hy926 was inhibited when cells were pre-incubated with collagen IV, suggesting that both compete for the same cell receptor. We present here for the first time the interaction of five leptospiral outer membrane proteins with several cell lines, and we conclude that LipL41 and OmpL1 may have an impact on leptospiral adhesion to mammalian cells and may mediate the colonization process in leptospiral pathogenesis.

Putative Pathogenic Genes of Leptospira interrogans and Leptospira weilii Isolated from Patients with Acute Febrile Illness

Leptospirosis is an important worldwide tropical disease caused by pathogenic Leptospira spp. The determination of virulence genes is important, as it influences patients' clinical manifestations and clinical outcomes. This case report focused on detecting the pathogenic genes of Leptospira in association with the clinical manifestations of patients at the Hospital Universiti Sains Malaysia, Malaysia, who presented with acute febrile illness. Two cases were found and, to the best of our knowledge, these were the first two cases in Malaysia in which patients presented with febrile illness were associated with successful Leptospira isolation from clinical samples. Both clinical isolates were identified by 16S rRNA sequencing as Leptospira weilii and Leptospira interrogans, respectively, and they were classified as pathogenic Leptospira by the presence of different pathogenic genes, based on a polymerase chain reaction (PCR) amplification of targeted genes. This report emphasizes that different infecting Leptospira species and the presence of different virulence factors cause a slight difference in clinical manifestations and laboratory findings of leptospirosis. Genomic sequencing and annotation revealed the detection of classical leptospiral virulence factor genes that were otherwise missed using PCR for detection of Leptospira weilii genome B208.

Insight into the Structure, Functions, and Dynamics of the Leptospira Outer Membrane Proteins with the Pathogenicity

Leptospirosis is a widespread zoonosis that frequently occurs in tropical and subtropical countries. Leptospira enters the host through wounds or mucous membranes and spreads to the whole body through the blood, causing systemic infection. Kidneys are the preferential site where Leptospira accumulates, especially in the renal interstitium and renal tubule epithelial cells. Clinical symptoms in humans include high fever, jaundice, renal failure, and severe multiple-organ failure (Weil’s syndrome). Surface-exposed antigens are located at the outermost layer of Leptospira and these potential virulence factors are likely involved in primary host-pathogen interactions, adhesion, and/or invasion. Using the knockout/knockdown techniques to the evaluation of pathogenicity in the virulence factor are the most direct and effective methods and many virulence factors are evaluated including lipopolysaccharides (LPS), Leptospira lipoprotein 32 (LipL32), Leptospira ompA domain protein 22 (Loa22), LipL41, LipL71, Leptospira immunoglobulin-like repeat A (LigA), LigB, and LipL21. In this review, we will discuss the structure, functions, and dynamics of these virulence factors and the roles of these virulence factors in Leptospira pathogenicity. In addition, a protein family with special Leucine-rich repeat (LRR) will also be discussed for their vital role in Leptospira pathogenicity. Finally, these surface-exposed antigens are discussed in the application of the diagnosis target for leptospirosis and compared with the serum microscope agglutination test (MAT), the gold standard for leptospirosis.

A Review on Host-Leptospira Interactions: What We Know and Future Expectations

Leptospirosis is a widespread zoonosis caused by pathogenic Leptospira spp. It is considered a neglected infectious disease of human and veterinary concern. Our group has been investigating proteins annotated as hypothetical, predicted to be located on the leptospiral surface. Because of their location, these proteins may have the ability to interact with various host components, which could allow establishment of the infection. These proteins act as adherence factors by binding to host receptor molecules, such as the extracellular matrix (ECM) components laminin and glycosaminoglycans to help bacterial colonization. Leptospira also interacts with the host fibrinolytic system, which has been demonstrated to be a powerful tool for invasion mechanisms. The interaction with fibrinogen and thrombin has been shown to reduce fibrin clot formation. Additionally, the degradation of coagulation cascade components by secreted proteases or by acquired surface plasmin could also play a role in reducing clot formation, hence facilitating dissemination during infection. Interaction with host complement system regulators also plays a role in helping bacteria to evade the immune system, facilitating invasion. Interaction of Leptospira to cell receptors, such as cadherins, can contribute to investigate molecules that participate in virulence. To achieve a better understanding of the host-pathogen interaction, leptospiral mutagenesis tools have been developed and explored. This work presents several proteins that mediate binding to components of the ECM, plasma, components of the complement system and cells, to gather research achievements that can be helpful in better understanding the mechanisms of leptospiral-host interactions and discuss genetic manipulation for Leptospira spp. aimed at protein function validation.