Catecholamine-Modulated Novel Surface-Exposed Adhesin LIC20035 of Leptospira spp. Binds Host Extracellular Matrix Components and Is Recognized by the Host during Infection

Exploring the complex interplay: gut microbiome, stress, and leptospirosis

Leptospirosis, a re-emerging zoonotic disease, remains a significant global health concern, especially amid floods and disasters such as the Kakhovka Dam destruction. As is known, the stress that occurs in the conditions of military conflicts among civilian and military personnel significantly affects susceptibility to infectious diseases and possibly even influences their course. This review aims to explore how the gut microbiome and stress mediators (such as catecholamines and corticosteroids) might impact the leptospirosis disease course. The review opens new horizons for research by elucidating the connections between the gut microbiome, stress, and 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.

Functional PAM sequence for DNA interference by CRISPR-Cas I-B system of Leptospira interrogans and the role of LinCas11b encoded within lincas8b

Pathogenic species of Leptospira are recalcitrant for genetic manipulation using conventional tools, and therefore there is a need to explore techniques of higher efficiency. Application of endogenous CRISPR-Cas tool is emerging and efficient; nevertheless, it is limited by a poor understanding of interference machinery in the bacterial genome and its associated protospacer adjacent motif (PAM). In this study, interference machinery of CRISPR-Cas subtype I-B (Lin_I-B) from L. interrogans was experimentally validated in E. coli using the various identified PAM (TGA, ATG, ATA). The overexpression of the Lin_I-B interference machinery in E. coli demonstrated that LinCas5, LinCas6, LinCas7, and LinCas8b can self-assemble on cognate CRISPR RNA to form an interference complex (LinCascade). Moreover, a robust interference of target plasmids containing a protospacer with a PAM suggested a functional LinCascade. We also recognized a small open reading frame within lincas8b that independently co-translates LinCas11b. A mutant variant of LinCascade^-Cas11b that lacks LinCas11b co-expression erred to mount target plasmid interference. At the same time, LinCas11b complementation in LinCascade^-Cas11b rescued target plasmid interference. Thus, the present study establishes Leptospira subtype I-B interference machinery to be functional and, soon, may pave the way for scientists to harness it as a programmable endogenous genetic manipulation tool.

Transcriptional analysis of CRISPR I-B arrays of Leptospira interrogans serovar Lai and its processing by Cas6

In the genome of various Leptospira interrogans serovars, the subtype I-B locus of CRISPR-Cas possesses either one or multiple CRISPR arrays. In silico database (CRISPRCasdb) for predicting CRISPR-Cas reveals seven CRISPR arrays in L. interrogans serovar Lai positioned between the two independent cas-operons. Here, we present the redefined repeat-spacer boundaries of the CRISPR subtype I-B locus of serovar Lai. Such refinement of boundaries of arrays in serovar Lai was done after comparison with the characterized array of another serovar Copenhageni and the manual analysis of CRISPR flanking sequences. Using the reverse transcription-PCR (RT-PCR), we account that the seven CRISPR are transcriptionally active in serovar Lai. Our RT-PCR and quantitative real-time PCR analysis of transcripts in serovar Lai indicated that seven CRISPR of subtype I-B transcribe together as a single precursor unit. Moreover, the cleavage of the two miniature pre-crRNA of the subtype I-B by Cas6 demonstrates the biogenesis of the expected size of mature crRNA essential for the guided interference of foreign DNA. This study features insight into transcription direction and the crRNA biogenesis in serovar Lai essential for RNA-mediated interference of invading nucleic acids.

Characterizing the transcripts of Leptospira CRISPR I-B array and its processing with endoribonuclease LinCas6

In Leptospira interrogans serovar Copenhageni, the CRISPR-Cas I-B locus possesses a CRISPR array between the two independent cas-operons. Using the reverse transcription-PCR and the in vitro endoribonuclease assay with Cas6 of Leptospira (LinCas6), we account that the CRISPR is transcriptionally active and is conventionally processed. The LinCas6 specifically excises at one site within the synthetic cognate repeat RNA or the repeats of precursor-CRISPR RNA (pre-crRNA) in the sense direction. In contrast, the antisense repeat RNA is cleaved at multiple sites. LinCas6 functions as a single turnover endoribonuclease on its repeat RNA substrate, where substitution of one of predicted active site residues (His38) resulted in reduced activity. This study highlights the comprehensive understanding of the Leptospira CRISPR array transcription and its processing by LinCas6 that is central to RNA-mediated CRISPR-Cas I-B adaptive immunity.

Role of Supramolecule ErpY-Like Lipoprotein of Leptospira in Thrombin-Catalyzed Fibrin Clot Inhibition and Binding to Complement Factors H and I, and Its Diagnostic Potential

Leptospirosis is one of the most widespread zoonoses caused by pathogenic Leptospira spp. In this study, we report that the LIC11966/ErpY-like lipoprotein is a surface-exposed outer membrane protein exclusively present in pathogenic species of Leptospira The recombinant ErpY (rErpY)-like protein is recognized by the immunoglobulins of confirmed leptospirosis sera of diverse hosts (human, bovine, and canine), suggesting the expression of the native leptospiral surface protein during infection. Circular dichroism of pure rErpY-like protein showed the secondary structural integrity to be uncompromised during the purification process. Analysis of the rErpY-like protein by native polyacrylamide gel electrophoresis, chemical cross-linking, dynamic light scattering, and field emission transmission electron microscopy demonstrated it undergoes supramolecular assembly. The rErpY-like protein can bind to diverse host extracellular matrices, and it presented a saturable and strong binding affinity (dissociation constant [K_D ] of 70.45 ± 4.13 nM) to fibrinogen, a central host plasma component involved in blood clotting. In the presence of the rErpY-like supramolecule, thrombin-catalyzed fibrin clot formation is inhibited up to 7%, implying its role in inhibiting blood coagulation during Leptospira infection. In addition, binding of the rErpY-like supramolecule to complement factors H and I suggests the protein also contributes to Leptospira evading innate host defense during infection by inactivating alternative complement pathways. This study reveals that rErpY-like protein is functionally active in the supramolecular state and performs moonlighting activity under the given in vitro conditions.

Insights to the Assembly of a Functionally Active Leptospiral ClpP1P2 Protease Complex along with Its ATPase Chaperone ClpX

Leptospira interrogans genome is predicted to encode multiple isoforms of caseinolytic proteases (ClpP1 and ClpP2). The ClpP proteins with the aid of its ATPase chaperone are known to be involved in establishing cellular proteostasis and have emerged as a target for developing new antibiotics. We report the molecular characterization of recombinant ClpP1 (rClpP1) and rClpP2 of Leptospira along with its ATPase chaperone rClpX. The two isoforms of rClpPs when coupled together in an equivalent concentration exhibit optimum activity on small fluorogenic peptide substrates, whereas the pure rClpP isoforms are enzymatically inactive. Isothermal titration calorimetry analysis suggests that the two rClpP isoforms bind each other moderately in a 1:1 stoichiometry with a dissociation constant of 2.02 ± 0.1 μM at 37 °C and is thermodynamically favored. Size exclusion chromatography fractionates the majority of pure rClpP1 at ≥308 kDa (14-21-mer) and the pure rClpP2 at 308 kDa (tetradecamer), whereas the functionally active rClpP isoform mixture fractionates as a tetradecamer. The distinct and unprecedented oligomeric form of rClpP1 was also evident through native-gel and dynamic light scattering. Moreover, the rClpP isoform mixture formed after the site-directed mutation of either or both the isoforms at one of the catalytic triad residues (Ser 98/97 to Ala 98/97) resulted in the complete loss of protease activity. The rClpP isoform mixture gets stimulated to degrade the casein substrate in the presence of rClpX and in an energy-dependent manner. On the contrary, pure rClpP1 or the rClpP2 isoform in association with rClpX are incapable of forming operative protease. The reported finding suggests that in Leptospira, the enzymatic activity of the rClpP protease complex in the presence or absence of cochaperone is performed solely by the tetradecamer structure which is hypothesized to be composed of 2-stacked ClpP heptameric rings, wherein each ring is a homo-oligomer of ClpP1 and ClpP2 subunits. Understanding the activities and regulation principle of multi-isoforms of ClpP in pathogenic bacteria may aid in intervening disease outcomes particularly to the co-evolving antibiotic resistance strains.