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By Susha Cheriyedath, M.Sc. Jul 31 2023 Reviewed by Benedette Cuffari, M.Sc.

A recent study published in PLOS Pathogens identifies the Leptospira membrane protein L36 (MPL36) as essential for its pathogenesis and, as a result, a potential target for future diagnostics and prophylactics.

Study:  MPL36, a major plasminogen (PLG) receptor in pathogenic Leptospira, has an essential role during infection.  Image Credit: Kateryna Kon / Shutterstock.com Background

The human plasminogen (PLG) system provides a proteolytic substrate for pathogen invasiveness and tissue damage, thereby increasing the virulence of various bacterial species. Sequestration of PLG and activation into plasmin (PLA) is important for bacterial survival, as PLA degrades fibrin clots, extracellular matrix (ECM) molecules, and the host's innate immunological proteins to enable bacteria to spread and evade immune responses ultimately.

Leptospirosis, a life-threatening infectious disease, is a zoonotic disease that accounts for over one million infections and about 60,000 deaths each year throughout the world. In severe forms of leptospirosis, patients will often experience severe hemorrhaging and acute kidney injury.

Leptospira enter the host through injured skin or mucous membranes and subsequently travel through viscous environments to ultimately reach the bloodstream. Thereafter, Leptospira participate in cellular adhesion, which is mediated by various surface proteins that interact with ECM components.

Previous studies indicate that many Leptospira proteins act as PLG receptors, some of which include outer membrane proteins (OMPs) like endostatin-like protein A (LenA), as well as Leptospiral immunoglobulin-like proteins A (LigA), LiGB, and LipL32.

To date, there remains a lack of data on the pathogenesis of leptospirosis, which has prevented the development of sensitive diagnostic instruments and efficient prophylactic treatments. The present study reports that MPL36 binds with PLG, promotes adherence to host cells, and degrades fibrinogen by converting bound PLG to PLA. About the study

The current study utilized Leptospira interrogans serovar Manilae strain L495 and its mutant stains, including Manilae mpl36 mutant complemented strain (Δmpl36+) and Leptospira biflexa serovar Patoc strain Patoc 1. These strains were cultured in Madin-Darby canine kidney (MDCK) cells, following which their growth curves were analyzed using dark-field microscopy, motility, and immunoblot assays.  

Recombinant MPL36 (rMPL36) protein was produced using E. coli expression. Intrinsic tryptophan fluorescence spectroscopy and nickel affinity chromatography evaluated the tertiary structure of rMPL36, rMPL36 aa41-305, and rMPL36 aa41-235. The binding capacity of rMPL36 was determined, and the conversion of PLG bound to rMPL36 into active PLA was evaluated.

The binding of rMPL36 to ECM proteins and PLG was determined by staining for fibronectin, laminin, PLG, and bovine serum albumin (BSA). The pathogenicity of Manilae wildtype (WT) and mutant strains was also evaluated in three-week-old male Golden Syrian hamsters. Related StoriesSARS-CoV-2 spike protein's role in lung injury unraveled: promising new approach uncoveredMitochondrial repair protein discovery may lead to new anti-aging treatmentsSalk researchers uncover molecular mechanisms of HIV drug resistance

The tertiary structure of sporulation-related repeat (SPOR) domains from leptospiral species was predicted using AlphaFold and PyMOL software ClustalX to match MPL36 SPOR domain sequences from various Leptospira species. In vivo data was analyzed using Prism 9, Fisher's exact test, and analysis of variance (ANOVA) to ecludate the mechanisms of rMPL36 binding to host components and BSA. MPL36 is a crucial target for leptopsirosis

The motility assay revealed that, as compared to wild-type cells, mpl36 mutant and complemented strains did not significantly differ in their motility or growth characteristics. Immunofluorescence staining confirmed the subcellular localization of MPL36 in Leptospira as an outer membrane protein in both wild-type and complement cells.

Immunoprecipitation studies revealed that rMPL36 exhibited significant binding to both rLigA and rLigB, whereas no binding was observed between rMPL36 and fibronectin nor laminin.

However, rMPL36 was found to effectively bind to human PLG as compared to other recombinant proteins that were used as positive and negative controls. Within rMPL36, the conserved SPOR domain, which is located at the last 70 amino acids of the protein, is essential for the binding between rMPL36 and PLG.

Hamsters that were infected with the wild-type strain died between eight and nine days following infection with Leptospira. Comparatively, mpl36 mutant hamsters who were infected with 108 leptospires survived without exhibiting any symptoms of leptospirosis, thereby demonstrating the significant role of MPL36 in leptospirosis.

Convalescent sera were obtained from Brazilian individuals with laboratory-confirmed severe leptospirosis. To this end, anti-MPL36 immunoglobulin M (IgM) and IgG were observed in leptospirosis patients’ samples as compared to sera from healthy individuals. Study takeaways

MPL36 is an outer membrane Leptospira protein that is capable of binding to PLG, degrading fibrinogen, and facilitating host infection. Despite these findings, additional research is needed to better understand leptospiral pathogenesis and advance diagnostic and prevention strategies. Journal reference: Zhu, W., Passalia, F. J., Hamond, C., et al. (2023). MPL36, a major plasminogen (PLG) receptor in pathogenic Leptospira, has an essential role during infection. PLOS Pathogens. doi:10.1371/journal.ppat.1011313 https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1011313

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Canucks, Boeser agree on new seven-year deal

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Canucks, Boeser agree on new seven-year deal

The Vancouver Canucks have come to terms with forward Brock Boeser on a new seven-year contract, carrying a $7.25 million AAV.

Canucks GM Patrik Allvin announced the deal on Tuesday during the first hour of NHL free agency. Boeser, 28, was an unrestricted free agent on a previously expiring contract.

Drafted by Vancouver 23rd overall in the 2015 NHL draft, Boeser has collected 204 goals and 434 points in 554 games with the Canucks to date. A top-six scoring threat, Boeser has elite playmaking skills and the potential to produce big numbers offensively. He had his best year offensively in 2023-24, producing 40 goals and 73 points in 81 games.

Boeser didn’t hit those marks again last season — settling for 25 goals and 50 points in 75 games — but was still second amongst teammates in output. He also plays a prominent role on Vancouver’s power play and when he can generate opportunities at 5-on-5, he is a true difference-maker up front for the Canucks.

The extension is a happy ending for Vancouver and Boeser. When the regular season ended, Boeser admitted “it’s tough to say” whether he’d be back with the Canucks. Boeser reportedly turned down a previous five-year extension offer with the club and Allvin subsequently looked into deals for him at the March trade deadline, with no takers. Boeser looked — and sounded — poised to explore his options on the open market.

Ultimately, Boeser decided to stay put by committing the best years of his career to the Canucks.

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Jake Allen agrees to 5-year deal with the Devils

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Jake Allen agrees to 5-year deal with the Devils

Jake Allen, one of the top goaltenders available entering free agency, is not heading to the market after agreeing to a five-year deal with the New Jersey Devils, sources told ESPN on Tuesday.

Allen’s average annual value on the deal is $1.8 million, sources told ESPN. That AAV allows the Devils to run back the same goaltending tandem for next season.

Jacob Markstrom has one year remaining on his contract for $4.125 million. Nico Daws is also under contract for next season, before becoming a restricted free agent next summer.

Several teams were interested in the 34-year-old veteran, whom sources said could have made more money on the open market. However, the deal with the Devils gives Allen long-term security. Allen has played for the Blues, Canadiens and Devils over his 12-year-career. He has started in 436 career games.

Last season, Allen started 29 games for the Devils, going 13-16-1 with a .906 save percentage, 2.66 GAA and four shutouts.

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Capitals sign Fehervary to 7-year, $42M extension

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Capitals sign Fehervary to 7-year, M extension

Washington Capitals defenseman Martin Fehervary signed a seven-year extension through the 2032-33 season that is worth $6 million annually, the team announced Tuesday.

Fehervary, who had one year of team control remaining, will enter the final season of a three-year bridge deal that will see him make $2.675 million before his new contract begins at the start of the 2026-27 season.

He finished the season with five goals and a career-high 25 points while logging 19 minutes. Fehervary also played a crucial role in the Capitals’ penalty kill by finishing with 245 short-handed minutes for a penalty kill that was fifth in the NHL with an 82% success rate.

Securing the 25-year-old Fehervary to a long-term deal means the Capitals now have seven players who have more than three years remaining on their current contracts.

It also means the Capitals front office has one less decision to make ahead of what is expected to be an active offseason in 2026 that will see the club have what PuckPedia projects to be $39.25 million in cap space.

That’s also the same offseason in which captain and NHL all-time leading goal scorer Alex Ovechkin‘s contract will come off their books along with that of defenseman John Carlson.

But until then, the Capitals have their entire top-six defensive unit under contract as they seek to improve upon a 2024-25 season that saw them finish atop the Metropolitan Division with 111 points before they lost in the Eastern Conference semifinal to the Carolina Hurricanes in five games.

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