A Trichomonas vaginalis Rhomboid Protease and Its Substrate Modulate Parasite Attachment and Cytolysis of Host Cells

TvLEGU-1 and TvLEGU-2 biomarkers for trichomoniasis are legumain-like cysteine peptidases secreted in vitro in a time-dependent manner

Trichomonas vaginalis is the causative agent of trichomoniasis, the most prevalent neglected parasitic sexually transmitted infection worldwide. Cysteine peptidases (CPs) are the most abundant proteins in the parasite degradome. Some CPs are virulence factors involved in trichomonal pathogenesis, cytoadherence, hemolysis, and cytotoxicity. Few are immunogenic and are found in the vaginal secretions of patients with trichomoniasis. Legumains are CPs of the C13 family of clan CD. T. vaginalis has 10 genes encoding legumain-like peptidases, and TvLEGU-1 and TvLEGU-2 have been characterized. Both are immunogenic and found in the vaginal secretions of patients with trichomoniasis that could be considered as potential biomarkers. Thus, our goal was to evaluate the effects of glucose on the proteolytic activity and secretion processes of TvLEGU-1 and TvLEGU-2. We performed in vitro secretion assays using different glucose concentrations, examined the presence and proteolytic activity of secreted legumains by Western blot and spectrofluorometry assays, and analyzed the localization of TvLEGU-1 and TvLEGU-2 in the parasites by indirect immunofluorescence. Our results show that TvLEGU-1 and TvLEGU-2 were secreted in vitro in a time-dependent manner and had legumain-like proteolytic activity that could contribute to parasite pathogenesis, supporting their relevance during infection and potential as trichomoniasis biomarkers.

Host-specific targets of Histomonas meleagridis antigens revealed by immunoprecipitation

Histomonas meleagridis, a protozoan parasite responsible for histomonosis (syn. Blackhead disease, histomoniasis), presents an increasing challenge for poultry health, particularly with the ban of licensed prophylactic and treatment options. Recent studies have explored H. meleagridis proteome, exoproteome, and surfaceome, linking molecular data to virulence and in vitro attenuation. Nevertheless, proteins involved in interactions with hosts remain largely unknown. In this study, we conducted immunoproteome analyses to identify key antigens involved in the humoral immune response of the parasite's main hosts, turkeys and chickens. Immunogenic proteins were isolated via immunoprecipitation using sera from chickens and turkeys that were vaccinated with a single attenuated strain and challenged with virulent strains of the protozoan, respectively. Mass spectrometry identified 155 putative H. meleagridis immunogenic proteins, of which 43 were recognized by sera from both hosts. In silico antigenicity screening (VaxElan) identified 33 pan-reactive antigens, with VaxiDL further highlighting 10 as potential vaccine candidates. Comparative analysis revealed host-specific immune responses, with 16 differential immunogenic proteins in chickens (6 specific to virulent and 10 to attenuated preparations) and 19 unique proteins in turkeys, all associated with virulent strains. These results enhance our understanding of H. meleagridis immunogenic protein dynamics and host-pathogen specificities, supporting the development of improved diagnostic tools and potential protective measures against the infection.

Iron triggers TvPI4P5K proteostasis and Arf-mediated cell membrane trafficking to regulate PIP2 signaling crucial for multiple pathogenic activities of the parasitic protozoan Trichomonas vaginalis

Trichomonas vaginalis is the etiologic agent of trichomoniasis, one of the most common non-viral sexually transmitted infections globally. Our previous work reported the role of phosphatidylinositol 4,5-bisphosphates (PIP2) signaling in the actin-dependent pathogenicity of T. vaginalis. This study further demonstrated that iron transiently regulated T. vaginalis phosphatidylinositol-4-phosphate 5-kinase (TvPI4P5K) proteostasis and its complex formation with an active ADP ribosylation factor TvArf220, facilitating co-trafficking to the plasma membrane, crucial for PIP2 production. In dominant-active HA-TvArf220 Q71L mutant, TvPI4P5K plasma membrane trafficking, PIP2 production, and intracellular calcium levels were increased, while these processes were inhibited in dominant-negative T31N mutant or those by Brefeldin A (BFA) treatment. Additionally, PIP2 replenishment reversed these inhibitions in the T31N mutant, suggesting the critical role of TvArf220 activation in PIP2-calcium signaling. Also, T31N mutant and BFA treatment impaired actin dynamics and cytoskeleton-dependent processes in T. vaginalis, further linking the role of TvArf220 to PIP2-calcium-dependent actin dynamics. Beyond cytoadherence, during host-parasite interactions, TvArf220 influenced both contact-dependent and -independent cytotoxicity, as well as phagocytotic capacity, contributing to the cytopathogenesis of human vaginal epithelial cells. Our findings underscore the key upstream regulation mechanisms of the PIP2 signaling, orchestrating the interplay between TvArf220-PIP2-calcium signaling and downstream actin cytoskeleton-driven pathogenicity in T. vaginalis.IMPORTANCETrichomonas vaginalis actin cytoskeleton-centric pathogenicity is regulated by the phosphatidylinositol 4,5-bisphosphates (PIP2)-triggered calcium signaling cascade in response to environmental iron, though the detailed mechanism by which iron modulates PIP2 signaling remains unclear. Our findings reveal that iron rapidly induces T. vaginalis phosphatidylinositol-4-phosphate 5-kinase (TvPI4P5K) translation followed by its degradation, while simultaneously activating TvArf220 binding, which facilitates TvPI4P5K localization to the plasma membrane for PIP2 production. In contrast to the TvArf220 Q71L mutant, the reduced PIP2 production, intracellular calcium, actin assembly, morphogenesis, and cytoadherence in the dominant-negative T31N mutant were recovered by PIP2 supplementation, indicating the essential role of TvArf220 in PIP2-dependent calcium signaling. Additionally, the contact-dependent or -independent cytotoxicity, along with the phagocytosis, was impaired in the TvPI4P5K- or TvArf220-deficient parasites, as well as in those treated with BAPTA or Latrunculin B. These findings highlight that TvArf220-mediated PIP2-calcium signaling cascade regulates actin cytoskeleton and cytopathogenicity of T. vaginalis. This study uncovers a novel pathogenic mechanism and suggests potential therapeutic targets for parasite control.

Trichomonas vaginalis extracellular vesicles up-regulate and directly transfer adherence factors promoting host cell colonization

Trichomonas vaginalis, a common sexually transmitted parasite that colonizes the human urogenital tract, secretes extracellular vesicles (TvEVs) that are taken up by human cells and are speculated to be taken up by parasites as well. While the crosstalk between TvEVs and human cells has led to insight into host:parasite interactions, roles for TvEVs in infection have largely been one-sided, with little known about the effect of TvEV uptake by T. vaginalis. Approximately 11% of infections are found to be coinfections of multiple T. vaginalis strains. Clinical isolates often differ in their adherence to and cytolysis of host cells, underscoring the importance of understanding the effects of TvEV uptake within the parasite population. To address this question, our lab tested the ability of a less adherent strain of T. vaginalis, G3, to take up fluorescently labeled TvEVs derived from both itself (G3-EVs) and TvEVs from a more adherent strain of the parasite (B7RC2-EVs). Here, we showed that TvEVs generated from the more adherent strain are internalized more efficiently compared to the less adherent strain. Additionally, preincubation of G3 parasites with B7RC2-EVs increases parasite aggregation and adherence to host cells. Transcriptomics revealed that TvEVs up-regulate expression of predicted parasite membrane proteins and identified an adherence factor, heteropolysaccharide binding protein (HPB2). Finally, using comparative proteomics and superresolution microscopy, we demonstrated direct transfer of an adherence factor, cadherin-like protein, from TvEVs to the recipient parasite's surface. This work identifies TvEVs as a mediator of parasite:parasite communication that may impact pathogenesis during mixed infections.

Trichomonas vaginalis Legumain-2, TvLEGU-2, Is an Immunogenic Cysteine Peptidase Expressed during Trichomonal Infection

Trichomonas vaginalis is the causative agent of trichomoniasis, the most prevalent nonviral, neglected sexually transmitted disease worldwide. T. vaginalis has one of the largest degradomes among unicellular parasites. Cysteine peptidases (CPs) are the most abundant peptidases, constituting 50% of the degradome. Some CPs are virulence factors recognized by antibodies in trichomoniasis patient sera, and a few are found in vaginal secretions that show fluctuations in glucose concentrations during infection. The CPs of clan CD in T. vaginalis include 10 genes encoding legumain-like peptidases of the C13 family. TvLEGU-2 is one of them and has been identified in multiple proteomes, including the immunoproteome obtained with Tv (+) patient sera. Thus, our goals were to assess the effect of glucose on TvLEGU-2 expression, localization, and in vitro secretion and determine whether TvLEGU-2 is expressed during trichomonal infection. We performed qRT-PCR assays using parasites grown under different glucose conditions. We also generated a specific anti-TvLEGU-2 antibody against a synthetic peptide of the most divergent region of this CP and used it in Western blot (WB) and immunolocalization assays. Additionally, we cloned and expressed the tvlegu-2 gene (TVAG_385340), purified the recombinant TvLEGU-2 protein, and used it as an antigen for immunogenicity assays to test human sera from patients with vaginitis. Our results show that glucose does not affect tvlegu-2 expression but does affect localization in different parasite organelles, such as the plasma membrane, Golgi complex, hydrogenosomes, lysosomes, and secretion vesicles. TvLEGU-2 is secreted in vitro, is present in vaginal secretions, and is immunogenic in sera from Tv (+) patients, suggesting its relevance during trichomonal infection.

PIP2 regulating calcium signal modulates actin cytoskeleton-dependent cytoadherence and cytolytic capacity in the protozoan parasite Trichomonas vaginalis

Trichomonas vaginalis is a prevalent causative agent that causes trichomoniasis leading to uropathogenic inflammation in the host. The crucial role of the actin cytoskeleton in T. vaginalis cytoadherence has been established but the associated signaling has not been fully elucidated. The present study revealed that the T. vaginalis second messenger PIP2 is located in the recurrent flagellum of the less adherent isolate and is more abundant around the cell membrane of the adherent isolates. The T. vaginalis phosphatidylinositol-4-phosphate 5-kinase (TvPI4P5K) with conserved activity phosphorylating PI(4)P to PI(4, 5)P2 was highly expressed in the adherent isolate and partially colocalized with PIP2 on the plasma membrane but with discrete punctate signals in the cytoplasm. Plasma membrane PIP2 degradation by phospholipase C (PLC)-dependent pathway concomitant with increasing intracellular calcium during flagellate-amoeboid morphogenesis. This could be inhibited by Edelfosine or BAPTA simultaneously repressing parasite actin assembly, morphogenesis, and cytoadherence with inhibitory effects similar to the iron-depleted parasite, supporting the significance of PIP2 and iron in T. vaginalis colonization. Intriguingly, iron is required for the optimal expression and cell membrane trafficking of TvPI4P5K for in situ PIP2 production, which was diminished in the iron-depleted parasites. TvPI4P5K-mediated PIP2 signaling may coordinate with iron to modulate T. vaginalis contact-dependent cytolysis to influence host cell viability. These observations provide novel insights into T. vaginalis cytopathogenesis during the host-parasite interaction.

Trichomonas vaginalis adhesion protein 65 (TvAP65) modulates parasite pathogenicity by interacting with host cell proteins

Trichomonas vaginalis (T. vaginalis) is a widespread and important sexually transmitted pathogen. Adherence to the surface of the host cell is the precondition forthis parasite's parasitism and pathogenicity. Adhesion protein 65 (TvAP65) plays a key role in the process of adhesion. However, how TvAP65 mediates the adhesion and pathogenicity of T. vaginalis to host cellsis unclear. In this study, we knocked down the expression of TvAP65 in trophozoites by small RNA interference. The number of T. vaginalis trophozoites adhering to VK2/E6E7 cells was decreased significantly, and the inhibition of VK2/E6E7 cells proliferation and VK2/E6E7 cells apoptosis and death induced by T. vaginalis were reduced, after the expression of TvAP65 was knocked down. Animal challenge experiments showed that the pathogenicity of trophozoites was decreased by passive immunization with anti-rTvAP65 PcAbs or blocking the TvAP65 protein. Immunofluorescence analysis showed that TvAP65 could bind to VK2/E6E7 cells. In order to screen the molecules interacting with TvAP65 on the host cells, we successfully constructed the cDNA library of VK2/E6E7 cells, and thirteen protein molecules interacting with TvAP65 were screened by yeast two-hybrid system. The interaction between TvAP65 and BNIP3 was further confirmed by coimmunoprecipitation and colocalization. When both TvAP65 and BNIP3 were knocked down by small RNA interference, the number of T. vaginalis adhering to VK2/E6E7 cells and the inhibition of VK2/E6E7 cells proliferation were significantly lower than those of the group with knockdown of TvAP65 or BNIP3 alone. Therefore, the interaction of TvAP65 and BNIP3 in the pathogenesis of T. vaginalis infecting host cells is not unique and involves other molecules. Our study elucidated that the interaction between TvAP65 and BNIP3 mediated the adhesion and pathogenicity of T. vaginalis to host cells, provided a basis for searching for the drug targets of anti-T. vaginalis, and afforded new ideas for the prevention and treatment of trichomoniasis.

Trichomonas vaginalis adherence phenotypes and extracellular vesicles impact parasite survival in a novel in vivo model of pathogenesis

Trichomonas vaginalis is a human infective parasite responsible for trichomoniasis-the most common, non-viral, sexually transmitted infection worldwide. T. vaginalis resides exclusively in the urogenital tract of both men and women. In women, T. vaginalis has been found colonizing the cervix and vaginal tract while in men it has been identified in the upper and lower urogenital tract and in secreted fluids such as semen, urethral discharge, urine, and prostatic fluid. Despite the over 270 million cases of trichomoniasis annually worldwide, T. vaginalis continues to be a highly neglected organism and thus poorly studied. Here we have developed a male mouse model for studying T. vaginalis pathogenesis in vivo by delivering parasites into the murine urogenital tract (MUT) via transurethral catheterization. Parasite burden was assessed ex-vivo using a nanoluciferase-based gene expression assay which allowed quantification of parasites pre- and post-inoculation. Using this model and read-out approach, we show that T. vaginalis can be found within MUT tissue up to 72 hrs post-inoculation. Furthermore, we also demonstrate that parasites that exhibit increased parasite adherence in vitro also have higher parasite burden in mice in vivo. These data provide evidence that parasite adherence to host cells aids in parasite persistence in vivo and molecular determinants found to correlate with host cell adherence in vitro are applicable to infection in vivo. Finally, we show that co-inoculation of T. vaginalis extracellular vesicles (TvEVs) and parasites results in higher parasite burden in vivo. These findings confirm our previous in vitro-based predictions that TvEVs assist the parasite in colonizing the host. The establishment of this pathogenesis model for T. vaginalis sets the stage for identifying and examining parasite factors that contribute to and influence infection outcomes.

An Atypical F-Actin Capping Protein Modulates Cytoskeleton Behaviors Crucial for Trichomonas vaginalis Colonization

Cytoadherence and migration are crucial for pathogens to establish colonization in the host. In contrast to a nonadherent isolate of Trichomonas vaginalis, an adherent one expresses more actin-related machinery proteins with more active flagellate-amoeboid morphogenesis, amoeba migration, and cytoadherence, activities that were abrogated by an actin assembly blocker. By immunoprecipitation coupled with label-free quantitative proteomics, an F-actin capping protein (T. vaginalis F-actin capping protein subunit α [TvFACPα]) was identified from the actin-centric interactome. His-TvFACPα was detected at the barbed end of a growing F-actin filament, which inhibited elongation and possessed atypical activity in binding G-actin in in vitro assays. TvFACPα partially colocalized with F-actin at the parasite pseudopod protrusion and formed a protein complex with α-actin through its C-terminal domain. Meanwhile, TvFACPα overexpression suppressed F-actin polymerization, amoeboid morphogenesis, and cytoadherence in this parasite. Ser2 phosphorylation of TvFACPα enriched in the amoeboid stage of adhered trophozoites was reduced by a casein kinase II (CKII) inhibitor. Site-directed mutagenesis and CKII inhibitor treatment revealed that Ser2 phosphorylation acts as a switching signal to alter TvFACPα actin-binding activity and the consequent actin cytoskeleton behaviors. Through CKII signaling, TvFACPα also controls the conversion of adherent trophozoites from amoeboid migration to the flagellate form with axonemal motility. Together, CKII-dependent Ser2 phosphorylation regulates TvFACPα binding to actin to fine-tune cytoskeleton dynamics and drive crucial behaviors underlying host colonization by T. vaginalis. IMPORTANCE Trichomoniasis is one of the most prevalent nonviral sexually transmitted diseases. T. vaginalis cytoadherence to urogenital epithelium cells is the first step in the colonization of the host. However, studies on the mechanisms of cytoadherence have focused mainly on the role of adhesion molecules, and their effects are limited when analyzed by loss- or gain-of-function assays. This study proposes an extra pathway in which the actin cytoskeleton mediated by a capping protein α-subunit may play roles in parasite morphogenesis, cytoadherence, and motility, which are crucial for colonization. Once the origin of the cytoskeleton dynamics could be manipulated, the consequent activities would be controlled as well. This mechanism may provide new potential therapeutic targets to impair this parasite infection and relieve the increasing impact of drug resistance on clinical and public health.

The interaction between adhesion protein 33 (TvAP33) and BNIP3 mediates the adhesion and pathogenicity of Trichomonas vaginalis to host cells

BACKGROUND

Trichomonas vaginalis is a widespread and important sexually transmitted pathogen. Adherence to the surface of the host cell is the precondition for the parasitism and pathogenicity of this parasite. Trichomonas vaginalis adhesion protein 33 (TvAP33) plays a key role in the process of adhesion, but how this protein mediates the adhesion and pathogenicity of T. vaginalis to host cells is unclear.

METHODS

The expression of TvAP33 in trophozoites was knocked down by small interfering RNA. VK2/E6E7 cells and mice infected with T. vaginalis were used to evaluate the pathogenicity of T. vaginalis. We constructed a complementary DNA library of VK2/E6E7 cells and screened the protein molecules interacting with TvAP33 by the yeast two-hybrid system. The interaction between TvAP33 and BNIP3 (Bcl-2 interacting protein 3) was analyzed by co-immunoprecipitation and colocalization.

RESULTS

Following knockdown of TvAP33 expression, the number of T. vaginalis trophozoites adhering to VK2/E6E7 cells decreased significantly, and the inhibition of VK2/E6E7 cell proliferation and VK2/E6E7 cell apoptosis and death induced by T. vaginalis were reduced. Animal challenge experiments showed that the pathogenicity of trophozoites decreased following passive immunization with TvAP33 antiserum or blocking of the TvAP33 protein. Immunofluorescence analysis revealed that TvAP33 could bind to VK2/E6E7 cells. Eighteen protein molecules interacting with TvAP33 were identified by the yeast two-hybrid system. The interaction between TvAP33 and BNIP3 was further confirmed by co-immunoprecipitation and colocalization. When the expression of both TvAP33 and BNIP3 in trophozoites was knocked down by small RNA interference, the number of T. vaginalis adhering to VK2/E6E7 cells and the inhibition of VK2/E6E7 cell proliferation were significantly lower compared to trophozoites with only knockdown of TvAP33 or only BNIP3. Therefore, the interaction of TvAP33 and BNIP3 in the pathogenesis of T. vaginalis infecting host cells is not unique and involves other molecules.

CONCLUSIONS

Our study showed that the interaction between TvAP33 and BNIP3 mediated the adhesion and pathogenicity of T. vaginalis to host cells, providing a basis for searching for drug targets for T. vaginalis as well as new ideas for the prevention and treatment of trichomoniasis.

Distinct features of the host-parasite interactions between nonadherent and adherent Trichomonas vaginalis isolates

Cytoadherence of Trichomonas vaginalis to human vaginal epithelial cells (hVECs) was previously shown to involve surface lipoglycans and several reputed adhesins on the parasite. Herein, we report some new observations on the host-parasite interactions of adherent versus nonadherent T. vaginalis isolates to hVECs. The binding of the TH17 adherent isolate to hVECs exhibited an initial discrete phase followed by an aggregation phase inhibited by lactose. T. vaginalis infection immediately induced surface expression of galectin-1 and -3, with extracellular amounts in the spent medium initially decreasing and then increasing thereafter over the next 60 min. Extracellular galectin-1 and -3 were detected on the parasite surface but only the TH17 adherent isolate could uptake galectin-3 via the lysosomes. Only the adherent isolate could morphologically transform from the round-up flagellate with numerous transient protrusions into a flat amoeboid form on contact with the solid surface. Cytochalasin D challenge revealed that actin organization was essential to parasite morphogenesis and cytoadherence. Real-time microscopy showed that parasite exploring and anchoring on hVECs via the axostyle may be required for initial cytoadherence. Together, the parasite cytoskeleton behaviors may collaborate with cell surface adhesion molecules for cytoadherence. The nonadherent isolate migrated faster than the adherent isolate, with motility transiently increasing in the presence of hVECs. Meanwhile, differential histone acetylation was detected between the two isolates. Also, TH17 without Mycoplasma symbiosis suggests that symbiont might not determine TH17 innate cytoadherence. Our findings regarding distinctive host-parasite interactions of the isolates may provide novel insights into T. vaginalis infection.

Omics Analyses of Trichomonas vaginalis Actin and Tubulin and Their Participation in Intercellular Interactions and Cytokinesis

Actin and tubulin proteins from Trichomonas vaginalis are crucial for morphogenesis and mitosis. This parasite has 10 and 11 genes coding bonafide actin and tubulin proteins, respectively. Hence, the goal of this work was to analyze these actin and tubulin genes, their expression at the mRNA and protein levels, and their parasite localization in intercellular interaction and cytokinesis. Representative bonafide actin (tvact1) and tubulin (tvtubα1) genes were cloned into and expressed in Escherichia coli. The recombinant proteins TvACT1r and TvTUBα1r were affinity purified and used as antigens to produce polyclonal antibodies. These antibodies were used in 1DE and 2DE WB and indirect immunofluorescence assays (IFA). By IFA, actin was detected as a ring on the periphery of ameboid, ovoid, and cold-induced cyst-like parasites, on pseudopods of amoeboid parasites, and in cytoplasmic extensions (filopodia) in cell–cell interactions. Tubulin was detected in the axostyle, flagellum, undulating membrane, and paradesmose during mitosis. Paradesmose was observed by IFA mainly during cytokinesis. By scanning electron microscopy, a tubulin-containing nanotubular structure similar to the tunneling nanotubes (TNTs) was also detected in the last stage of cytokinesis. In conclusion, actin and tubulin are multigene families differentially expressed that play important roles in intercellular interactions and cytokinesis.

Brucella abortus Encodes an Active Rhomboid Protease: Proteome Response after Rhomboid Gene Deletion

Rhomboids are intramembrane serine proteases highly conserved in the three domains of life. Their key roles in eukaryotes are well understood but their contribution to bacterial physiology is still poorly characterized. Here we demonstrate that Brucella abortus, the etiological agent of the zoonosis called brucellosis, encodes an active rhomboid protease capable of cleaving model heterologous substrates like Drosophila melanogaster Gurken and Providencia stuartii TatA. To address the impact of rhomboid deletion on B. abortus physiology, the proteomes of mutant and parental strains were compared by shotgun proteomics. About 50% of the B. abortus predicted proteome was identified by quantitative proteomics under two experimental conditions and 108 differentially represented proteins were detected. Membrane associated proteins that showed variations in concentration in the mutant were considered as potential rhomboid targets. This class included nitric oxide reductase subunit C NorC (Q2YJT6) and periplasmic protein LptC involved in LPS transport to the outer membrane (Q2YP16). Differences in secretory proteins were also addressed. Differentially represented proteins included a putative lytic murein transglycosylase (Q2YIT4), nitrous-oxide reductase NosZ (Q2YJW2) and high oxygen affinity Cbb3-type cytochrome c oxidase subunit (Q2YM85). Deletion of rhomboid had no obvious effect in B. abortus virulence. However, rhomboid overexpression had a negative impact on growth under static conditions, suggesting an effect on denitrification enzymes and/or high oxygen affinity cytochrome c oxidase required for growth in low oxygen tension conditions.

VPS32, a member of the ESCRT complex, modulates adherence to host cells in the parasite Trichomonas vaginalis by affecting biogenesis and cargo sorting of released extracellular vesicles

Trichomonas vaginalis is a common sexually transmitted extracellular parasite that adheres to epithelial cells in the human urogenital tract. Extracellular vesicles (EVs) have been described as important players in the pathogenesis of this parasite as they deliver proteins and RNA into host cells and modulate parasite adherence. EVs are heterogeneous membrane vesicles released from virtually all cell types that collectively represent a new dimension of intercellular communication. The Endosomal Sorting Complex Required for Transport (ESCRT) machinery contributes to several key mechanisms in which it reshapes membranes. Based on this, some components of the ESCRT have been implicated in EVs biogenesis in other cells. Here, we demonstrated that VPS32, a member of ESCRTIII complex, contribute to the biogenesis and cargo sorting of extracellular vesicles in the parasite T. vaginalis. Moreover, we observe that parasites overexpressing VPS32 have a striking increase in adherence to host cells compared to control parasites; demonstrating a key role for this protein in mediating host: parasite interactions. These results provide valuable information on the molecular mechanisms involved in extracellular vesicles biogenesis, cargo-sorting, and parasite pathogenesis.

Microparticles from human the lower airway show inhibitory activity against respiratory syncytial virus

Airway microparticles (MPs) have been shown previously to inhibit influenza virus by trapping virions on their surface through their surface viral receptor. It was hypothesized that airway MPs may carry most of the epithelial cell surface molecules, including receptors for respiratory viruses, and may be able to inhibit various respiratory viruses. We show here that MPs from human bronchoalveolar lavage (BAL) can inhibit respiratory syncytial virus (RSV). Those MPs stained positive for the RSV receptor, CX3CR1. Furthermore, incubating the MPs with a monoclonal antibody against CX3CR1 reduced the anti-RSV activity. These data indicate that MPs can contribute to respiratory innate antiviral defense.

Recent advances in the molecular biology of the protist parasite Trichomonas vaginalis

Trichomonas vaginalis is an anaerobic/microaerophilic protist parasite which causes trichomoniasis, one of the most prevalent sexually transmitted diseases worldwide. T. vaginalis not only is important as a human pathogen but also is of great biological interest because of its peculiar cell biology and metabolism, in earlier times fostering the erroneous notion that this microorganism is at the root of eukaryotic evolution. This review summarizes the major advances in the last five years in the T. vaginalis field with regard to genetics, molecular biology, ecology, and pathogenicity of the parasite.

A Novel Trichomonas vaginalis Surface Protein Modulates Parasite Attachment via Protein:Host Cell Proteoglycan Interaction

Trichomonas vaginalis is a highly prevalent, sexually transmitted parasite which adheres to mucosal epithelial cells to colonize the human urogenital tract. Despite adherence being crucial for this extracellular parasite to thrive within the host, relatively little is known about the mechanisms or key molecules involved in this process. Here, we have identified and characterized a T. vaginalis hypothetical protein, TVAG_157210 (TvAD1), as a surface protein that plays an integral role in parasite adherence to the host. Quantitative proteomics revealed TvAD1 to be ∼4-fold more abundant in parasites selected for increased adherence (MA parasites) than the isogenic parental (P) parasite line. De novo modeling suggested that TvAD1 binds N-acetylglucosamine (GlcNAc), a sugar comprising host glycosaminoglycans (GAGs). Adherence assays utilizing GAG-deficient cell lines determined that host GAGs, primarily heparan sulfate (HS), mediate adherence of MA parasites to host cells. TvAD1 knockout (KO) parasites, generated using CRISPR-Cas9, were found to be significantly reduced in host cell adherence, a phenotype that is rescued by overexpression of TvAD1 in KO parasites. In contrast, there was no significant difference in parasite adherence to GAG-deficient lines by KO parasites compared with wild-type, which is contrary to that observed for KO parasites overexpressing TvAD1. Isothermal titration calorimetric (ITC) analysis showed that TvAD1 binds to HS, indicating that TvAD1 mediates host cell adherence via HS interaction. In addition to characterizing the role of TvAD1 in parasite adherence, these studies reveal a role for host GAG molecules in T. vaginalis adherence.IMPORTANCE The ability of the sexually transmitted parasite Trichomonas vaginalis to adhere to its human host is critical for establishing and maintaining an infection. Yet how parasites adhere to host cells is poorly understood. In this study, we employed a novel adherence selection method to identify proteins involved in parasite adherence to the host. This method led to the identification of a protein, with no previously known function, that is more abundant in parasites with increased capacity to bind host cells. Bioinformatic modeling and biochemical analyses revealed that this protein binds a common component on the host cell surface proteoglycans. Subsequent creation of parasites that lack this protein directly demonstrated that the protein mediates parasite adherence via an interaction with host cell proteoglycans. These findings both demonstrate a role for this protein in T. vaginalis adherence to the host and shed light on host cell molecules that participate in parasite colonization.

Designed Parasite-Selective Rhomboid Inhibitors Block Invasion and Clear Blood-Stage Malaria

Rhomboid intramembrane proteases regulate pathophysiological processes, but their targeting in a disease context has never been achieved. We decoded the atypical substrate specificity of malaria rhomboid PfROM4, but found, unexpectedly, that it results from "steric exclusion": PfROM4 and canonical rhomboid proteases cannot cleave each other's substrates due to reciprocal juxtamembrane steric clashes. Instead, we engineered an optimal sequence that enhanced proteolysis >10-fold, and solved high-resolution structures to discover that boronates enhance inhibition >100-fold. A peptide boronate modeled on our "super-substrate" carrying one "steric-excluding" residue inhibited PfROM4 but not human rhomboid proteolysis. We further screened a library to discover an orthogonal alpha-ketoamide that potently inhibited PfROM4 but not human rhomboid proteolysis. Despite the membrane-immersed target and rapid invasion, ultrastructural analysis revealed that single-dosing blood-stage malaria cultures blocked host-cell invasion and cleared parasitemia. These observations establish a strategy for designing parasite-selective rhomboid inhibitors and expose a druggable dependence on rhomboid proteolysis in non-motile parasites.

Bacterial rhomboid proteases mediate quality control of orphan membrane proteins

Although multiprotein membrane complexes play crucial roles in bacterial physiology and virulence, the mechanisms governing their quality control remain incompletely understood. In particular, it is not known how unincorporated, orphan components of protein complexes are recognised and eliminated from membranes. Rhomboids, the most widespread and largest superfamily of intramembrane proteases, are known to play key roles in eukaryotes. In contrast, the function of prokaryotic rhomboids has remained enigmatic. Here, we show that the Shigella sonnei rhomboid proteases GlpG and the newly identified Rhom7 are involved in membrane protein quality control by specifically targeting components of respiratory complexes, with the metastable transmembrane domains (TMDs) of rhomboid substrates protected when they are incorporated into a functional complex. Initial cleavage by GlpG or Rhom7 allows subsequent degradation of the orphan substrate. Given the occurrence of this strategy in an evolutionary ancient organism and the presence of rhomboids in all domains of life, it is likely that this form of quality control also mediates critical events in eukaryotes and protects cells from the damaging effects of orphan proteins.

Reduced expression of a rhomboid protease, EhROM1, correlates with changes in the submembrane distribution and size of the Gal/GalNAc lectin subunits in the human protozoan parasite, Entamoeba histolytica

Entamoeba histolytica is a food- and waterborne parasite that causes amebic dysentery and amoebic liver abscesses. Adhesion is one of the most important virulence functions as it facilitates motility, colonization of host, destruction of host tissue, and uptake of nutrients by the parasite. The parasite cell surface adhesin, the Gal/GalNAc lectin, facilitates parasite-host interaction by binding to galactose or N-acetylgalactosamine residues on host components. It is composed of heavy (Hgl), intermediate (Igl), and light (Lgl) subunits. Igl is constitutively localized to lipid rafts (cholesterol-rich membrane domains), whereas Hgl and Lgl transiently associate with rafts. When all three subunits are localized to rafts, galactose-sensitive adhesion is enhanced. Thus, submembrane location may regulate the function of this adhesion. Rhomboid proteases are a conserved family of intramembrane proteases that also participate in the regulation of parasite-host interactions. In E. histolytica, one rhomboid protease, EhROM1, cleaves Hgl as a substrate, and knockdown of its expression inhibits parasite-host interactions. Since rhomboid proteases are found within membranes, it is not surprising that lipid composition regulates their activity and enzyme-substrate binding. Given the importance of the lipid environment for both rhomboid proteases and the Gal/GalNAc lectin, we sought to gain insight into the relationship between rhomboid proteases and submembrane location of the lectin in E. histolytica. We demonstrated that EhROM1, itself, is enriched in highly buoyant triton-insoluble membranes reminiscent of rafts. Reducing rhomboid protease activity, either pharmacologically or genetically, correlated with an enrichment of Hgl and Lgl in rafts. In a mutant cell line with reduced EhROM1 expression, there was also a significant augmentation of the level of all three Gal/GalNAc subunits on the cell surface and an increase in the molecular weight of Hgl and Lgl. Overall, the study provides insight into the molecular mechanisms governing parasite-host adhesion for this pathogen.

Rhomboid intramembrane protease YqgP licenses bacterial membrane protein quality control as adaptor of FtsH AAA protease

Magnesium homeostasis is essential for life and depends on magnesium transporters, whose activity and ion selectivity need to be tightly controlled. Rhomboid intramembrane proteases pervade the prokaryotic kingdom, but their functions are largely elusive. Using proteomics, we find that Bacillus subtilis rhomboid protease YqgP interacts with the membrane‐bound ATP‐dependent processive metalloprotease FtsH and cleaves MgtE, the major high‐affinity magnesium transporter in B. subtilis. MgtE cleavage by YqgP is potentiated in conditions of low magnesium and high manganese or zinc, thereby protecting B. subtilis from Mn²⁺/Zn²⁺ toxicity. The N‐terminal cytosolic domain of YqgP binds Mn²⁺ and Zn²⁺ ions and facilitates MgtE cleavage. Independently of its intrinsic protease activity, YqgP acts as a substrate adaptor for FtsH, a function that is necessary for degradation of MgtE. YqgP thus unites protease and pseudoprotease function, hinting at the evolutionary origin of rhomboid pseudoproteases such as Derlins that are intimately involved in eukaryotic ER‐associated degradation (ERAD). Conceptually, the YqgP‐FtsH system we describe here is analogous to a primordial form of “ERAD” in bacteria and exemplifies an ancestral function of rhomboid‐superfamily proteins.

Ten catalytic snapshots of rhomboid intramembrane proteolysis from gate opening to peptide release

Protein cleavage inside the cell membrane triggers various patho-physiological signaling pathways, but the mechanism of catalysis is poorly understood. We solved ten structures of the Escherichia coli rhomboid protease in a bicelle membrane undergoing time-resolved steps that encompass the entire proteolytic reaction on a transmembrane substrate and an aldehyde inhibitor. Extensive gate opening accompanied substrate, but not inhibitor, binding, revealing that substrates and inhibitors take different paths to the active site. Catalysis unexpectedly commenced with, and was guided through subsequent catalytic steps by, motions of an extracellular loop, with local contributions from active site residues. We even captured the elusive tetrahedral intermediate that is uncleaved but covalently attached to the catalytic serine, around which the substrate was forced to bend dramatically. This unexpectedly stable intermediate indicates rhomboid catalysis uses an unprecedented reaction coordinate that may involve mechanically stressing the peptide bond, and could be selectively targeted by inhibitors.

Characterization of the BspA and Pmp protein family of trichomonads

Background

Trichomonas vaginalis is a human-infecting trichomonad and as such the best studied and the only for which the full genome sequence is available considering its parasitic lifestyle, T. vaginalis encodes an unusually high number of proteins. Many gene families are massively expanded and some genes are speculated to have been acquired from prokaryotic sources. Among the latter are two gene families that harbour domains which share similarity with proteins of Bacteroidales/Spirochaetales and Chlamydiales: the BspA and the Pmp proteins, respectively.

Results

We sequenced the transcriptomes of five trichomonad species and screened for the presence of BspA and Pmp domain-containing proteins and characterized individual candidate proteins from both families in T. vaginalis. Here, we demonstrate that (i) BspA and Pmp domain-containing proteins are universal to trichomonads, but specifically expanded in T. vaginalis; (ii) in line with a concurrent expansion of the endocytic machinery, there is a high number of BspA and Pmp proteins which carry C-terminal endocytic motifs; and (iii) both families traffic through the ER and have the ability to increase adhesion performance in a non-virulent T. vaginalis strain and Tetratrichomonas gallinarum by a so far unknown mechanism.

Conclusions

Our results initiate the functional characterization of these two broadly distributed protein families and help to better understand the origin and evolution of BspA and Pmp domains in trichomonads.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3660-z) contains supplementary material, which is available to authorized users.

Rhomboid distorts lipids to break the viscosity-imposed speed limit of membrane diffusion

Enzymes that cut proteins inside membranes regulate diverse cellular events, including cell signaling, homeostasis, and host-pathogen interactions. Adaptations that enable catalysis in this exceptional environment are poorly understood. We visualized single molecules of multiple rhomboid intramembrane proteases and unrelated proteins in living cells (human and Drosophila) and planar lipid bilayers. Notably, only rhomboid proteins were able to diffuse above the Saffman-Delbrück viscosity limit of the membrane. Hydrophobic mismatch with the irregularly shaped rhomboid fold distorted surrounding lipids and propelled rhomboid diffusion. The rate of substrate processing in living cells scaled with rhomboid diffusivity. Thus, intramembrane proteolysis is naturally diffusion-limited, but cells mitigate this constraint by using the rhomboid fold to overcome the "speed limit" of membrane diffusion.

A Novel Cadherin-like Protein Mediates Adherence to and Killing of Host Cells by the Parasite Trichomonas vaginalis

Trichomonas vaginalis, a prevalent sexually transmitted parasite, adheres to and induces cytolysis of human mucosal epithelial cells. We have characterized a hypothetical protein, TVAG_393390, with predicted tertiary structure similar to that of mammalian cadherin proteins involved in cell-cell adherence. TVAG_393390, renamed cadherin-like protein (CLP), contains a calcium-binding site at a position conserved in cadherins. CLP is surface localized, and its mRNA and protein levels are significantly upregulated upon parasite adherence to host cells. To test the roles of CLP and its calcium-binding dependency during host cell adherence, we first demonstrated that wild-type CLP (CLP) binds calcium with a high affinity, whereas the calcium-binding site mutant protein (CLP-mut) does not. CLP and CLP-mut constructs were then used to overexpress these proteins in T. vaginalis Parasites overexpressing CLP have ∼3.5-fold greater adherence to host cells than wild-type parasites, and this increased adherence is ablated by mutating the calcium-binding site. Additionally, competition with recombinant CLP decreased parasite binding to host cells. We also found that overexpression of CLP induced parasite aggregation which was further enhanced in the presence of calcium, whereas CLP-mut overexpression did not affect aggregation. Lastly, parasites overexpressing wild-type CLP induced killing of host cells ∼2.35-fold, whereas parasites overexpressing CLP-mut did not have this effect. These analyses describe the first parasitic CLP and demonstrate a role for this protein in mediating parasite-parasite and host-parasite interactions. T. vaginalis CLP may represent convergent evolution of a parasite protein that is functionally similar to the mammalian cell adhesion protein cadherin, which contributes to parasite pathogenesis.IMPORTANCE The adherence of pathogens to host cells is critical for colonization of the host and establishing infection. Here we identify a protein with no known function that is more abundant on the surface of parasites that are better at binding host cells. To interrogate a predicted function of this protein, we utilized bioinformatic protein prediction programs which allowed us to uncover the first cadherin-like protein (CLP) found in a parasite. Cadherin proteins are conserved metazoan proteins with central roles in cell-cell adhesion, development, and tissue structure maintenance. Functional characterization of this CLP from the unicellular parasite Trichomonas vaginalis demonstrated that the protein mediates both parasite-parasite and parasite-host adherence, which leads to an enhanced killing of host cells by T. vaginalis Our findings demonstrate the presence of CLPs in unicellular pathogens and identify a new host cell binding protein family in a human-infective parasite.

Trichomonas vaginalis: Pathogenesis, Symbiont Interactions, and Host Cell Immune Responses

The parasite Trichomonas vaginalis (Tv) causes a highly prevalent sexually transmitted infection. As an extracellular pathogen, the parasite mediates adherence to epithelial cells to colonize the human host. In addition, the parasite interfaces with the host immune system and the vaginal microbiota. Modes of Tv pathogenesis include damage to host tissue mediated by parasite killing of host cells, disruption of steady-state vaginal microbial ecology, and eliciting inflammation by activating the host immune response. Recent Tv research has uncovered new players that contribute to multifactorial mechanisms of host-parasite adherence and killing, and has examined the relationship between Tv and vaginal bacteria. Mechanisms that may lead to parasite recognition and killing, or the evasion of host immune cells, have also been revealed.

A Cell Surface Aggregation-Promoting Factor from Lactobacillus gasseri Contributes to Inhibition of Trichomonas vaginalis Adhesion to Human Vaginal Ectocervical Cells

Trichomoniasis, a prevalent sexually transmitted infection, is commonly symptomatic in women. The causative agent is Trichomonas vaginalis, an extracellular protozoan parasite. The host-protective mechanisms and molecules of vaginal lactobacilli that counteract this pathogen are largely unknown. This study examines the inhibition promoted by Lactobacillus gasseri against the adhesion of T. vaginalis to host cells, a critical virulence aspect of this pathogen. We observed that the vaginal strain L. gasseri ATCC 9857 is highly inhibitory by various contact-dependent mechanisms and that surface proteins are largely responsible for this inhibitory phenotype. We found that the aggregation-promoting factor APF-2 from these bacteria significantly contributes to inhibition of the adhesion of T. vaginalis to human vaginal ectocervical cells. Understanding the molecules and mechanisms used by lactobacilli to protect the host against T. vaginalis might help in the development of novel and specific therapeutic strategies that take advantage of the natural microbiota.

Haloferax volcanii Proteome Response to Deletion of a Rhomboid Protease Gene

Rhomboids are conserved intramembrane serine proteases involved in cell signaling processes. Their role in prokaryotes is scarcely known and remains to be investigated in Archaea. We previously constructed a rhomboid homologue deletion mutant (ΔrhoII) in Haloferax volcanii, which showed reduced motility, increased novobiocin sensitivity, and an N- glycosylation defect. To address the impact of rhoII deletion on H. volcanii physiology, the proteomes of mutant and parental strains were compared by shotgun proteomics. A total of 1847 proteins were identified (45.8% of H. volcanii predicted proteome), from which 103 differed in amount. Additionally, the mutant strain evidenced 99 proteins with altered electrophoretic migration, which suggested differential post-translational processing/modification. Integral membrane proteins that evidenced variations in concentration, electrophoretic migration, or semitryptic cleavage in the mutant were considered as potential RhoII targets. These included a PrsW protease homologue (which was less stable in the mutant strain), a predicted halocyanin, and six integral membrane proteins potentially related to the mutant glycosylation (S-layer glycoprotein, Agl15) and cell adhesion/motility (flagellin1, HVO_1153, PilA1, and PibD) defects. This study investigated for the first time the impact of a rhomboid protease on the whole proteome of an organism.

Neutrophils kill the parasite Trichomonas vaginalis using trogocytosis

T. vaginalis, a human-infective parasite, causes the most common nonviral sexually transmitted infection (STI) worldwide and contributes to adverse inflammatory disorders. The immune response to T. vaginalis is poorly understood. Neutrophils (polymorphonuclear cells [PMNs]) are the major immune cell present at the T. vaginalis-host interface and are thought to clear T. vaginalis. However, the mechanism of PMN clearance of T. vaginalis has not been characterized. We demonstrate that human PMNs rapidly kill T. vaginalis in a dose-dependent, contact-dependent, and neutrophil extracellular trap (NET)-independent manner. In contrast to phagocytosis, we observed that PMN killing of T. vaginalis involves taking "bites" of T. vaginalis prior to parasite death, using trogocytosis to achieve pathogen killing. Both trogocytosis and parasite killing are dependent on the presence of PMN serine proteases and human serum factors. Our analyses provide the first demonstration, to our knowledge, of a mammalian phagocyte using trogocytosis for pathogen clearance and reveal a novel mechanism used by PMNs to kill a large, highly motile target.

Dynamic secretome of Trichomonas vaginalis: Case study of β-amylases

The secretion of virulence factors by parasitic protists into the host environment plays a fundamental role in multifactorial host-parasite interactions. Several effector proteins are known to be secreted by Trichomonas vaginalis, a human parasite of the urogenital tract. However, a comprehensive profiling of the T. vaginalis secretome remains elusive, as do the mechanisms of protein secretion. In this study, we used high-resolution label-free quantitative MS to analyze the T. vaginalis secretome, considering that secretion is a time- and temperature-dependent process, to define the cutoff for secreted proteins. In total, we identified 2 072 extracellular proteins, 89 of which displayed significant quantitative increases over time at 37 °C. These 89 bona fide secreted proteins were sorted into 13 functional categories. Approximately half of the secreted proteins were predicted to possess transmembrane helixes. These proteins mainly include putative adhesins and leishmaniolysin-like metallopeptidases. The other half of the soluble proteins include several novel potential virulence factors, such as DNaseII, pore-forming proteins, and β-amylases. Interestingly, current bioinformatic tools predicted the secretory signal in only 18% of the identified T. vaginalis-secreted proteins. Therefore, we used β-amylases as a model to investigate the T. vaginalis secretory pathway. We demonstrated that two β-amylases (BA1 and BA2) are transported via the classical endoplasmic reticulum-to-Golgi pathways, and in the case of BA1, we showed that the protein is glycosylated with multiple N-linked glycans of Hex5HexNAc2 structure. The secretion was inhibited by brefeldin A but not by FLI-06. Another two β-amylases (BA3 and BA4), which are encoded in the T. vaginalis genome but absent from the secretome, were targeted to the lysosomal compartment. Collectively, under defined in vitro conditions, our analysis provides a comprehensive set of constitutively secreted proteins that can serve as a reference for future comparative studies, and it provides the first information about the classical secretory pathway in this parasite.

CRISPR/Cas9-mediated gene modification and gene knock out in the human-infective parasite Trichomonas vaginalis

The sexually-transmitted parasite Trichomonas vaginalis infects ~1/4 billion people worldwide. Despite its prevalence and myriad adverse outcomes of infection, the mechanisms underlying T. vaginalis pathogenesis are poorly understood. Genetic manipulation of this single-celled eukaryote has been hindered by challenges presented by its complex, repetitive genome and inefficient methods for introducing DNA (i.e. transfection) into the parasite. Here, we have developed methods to increase transfection efficiency using nucleofection, with the goal of efficiently introducing multiple DNA elements into a single T. vaginalis cell. We then created DNA constructs required to express several components essential to drive CRISPR/Cas9-mediated DNA modification: guide RNA (gRNA), the Cas9 endonuclease, short oligonucleotides and large, linearized DNA templates. Using these technical advances, we have established CRISPR/Cas9-mediated repair of mutations in genes contained on circular DNA plasmids harbored by the parasite. We also engineered CRISPR/Cas9 directed homologous recombination to delete (i.e. knock out) two non-essential genes within the T. vaginalis genome. This first report of the use of the CRISPR/Cas9 system in T. vaginalis greatly expands the ability to manipulate the genome of this pathogen and sets the stage for testing of the role of specific genes in many biological processes.

Epigenetics regulates transcription and pathogenesis in the parasite Trichomonas vaginalis

Trichomonas vaginalis is a common sexually transmitted parasite that colonizes the human urogenital tract. Infections range from asymptomatic to highly inflammatory, depending on the host and the parasite strain. Different T. vaginalis strains vary greatly in their adherence and cytolytic capacities. These phenotypic differences might be attributed to differentially expressed genes as a consequence of extra-genetic variation, such as epigenetic modifications. In this study, we explored the role of histone acetylation in regulating gene transcription and pathogenesis in T. vaginalis. Here, we show that histone 3 lysine acetylation (H3KAc) is enriched in nucleosomes positioned around the transcription start site of active genes (BAP1 and BAP2) in a highly adherent parasite strain; compared with the low acetylation abundance in contrast to that observed in a less-adherent strain that expresses these genes at low levels. Additionally, exposition of less-adherent strain with a specific histone deacetylases inhibitor, trichostatin A, upregulated the transcription of BAP1 and BAP2 genes in concomitance with an increase in H3KAc abundance and chromatin accessibility around their transcription start sites. Moreover, we demonstrated that the binding of initiator binding protein, the transcription factor responsible for the initiation of transcription of ~75% of known T. vaginalis genes, depends on the histone acetylation state around the metazoan-like initiator to which initiator binding protein binds. Finally, we found that trichostatin A treatment increased parasite aggregation and adherence to host cells. Our data demonstrated for the first time that H3KAc is a permissive histone modification that functions to mediate both transcription and pathogenesis of the parasite T. vaginalis.

Rhomboid proteases in human disease: Mechanisms and future prospects

Rhomboids are intramembrane serine proteases that cleave the transmembrane helices of substrate proteins, typically releasing luminal/extracellular domains from the membrane. They are conserved in all branches of life and there is a growing recognition of their association with a wide range of human diseases. Human rhomboids, for example, have been implicated in cancer, metabolic disease and neurodegeneration, while rhomboids in apicomplexan parasites appear to contribute to their invasion of host cells. Recent advances in our knowledge of the structure and the enzyme function of rhomboids, and increasing efforts to identify specific inhibitors, are beginning to provide important insight into the prospect of rhomboids becoming future therapeutic targets. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Sensitive Versatile Fluorogenic Transmembrane Peptide Substrates for Rhomboid Intramembrane Proteases

Rhomboid proteases are increasingly being explored as potential drug targets, but their potent and specific inhibitors are not available, and strategies for inhibitor development are hampered by the lack of widely usable and easily modifiable in vitro activity assays. Here we address this bottleneck and report on the development of new fluorogenic transmembrane peptide substrates, which are cleaved by several unrelated rhomboid proteases, can be used both in detergent micelles and in liposomes, and contain red-shifted fluorophores that are suitable for high-throughput screening of compound libraries. We show that nearly the entire transmembrane domain of the substrate is important for efficient cleavage, implying that it extensively interacts with the enzyme. Importantly, we demonstrate that in the detergent micelle system, commonly used for the enzymatic analyses of intramembrane proteolysis, the cleavage rate strongly depends on detergent concentration, because the reaction proceeds only in the micelles. Furthermore, we show that the catalytic efficiency and selectivity toward a rhomboid substrate can be dramatically improved by targeted modification of the sequence of its P5 to P1 region. The fluorogenic substrates that we describe and their sequence variants should find wide use in the detection of activity and development of inhibitors of rhomboid proteases.

Auranofin inactivates Trichomonas vaginalis thioredoxin reductase and is effective against trichomonads in vitro and in vivo

Trichomoniasis, caused by the protozoan parasite Trichomonas vaginalis, is the most common, non-viral, sexually transmitted infection in the world, but only two closely related nitro drugs are approved for its treatment. New antimicrobials against trichomoniasis remain an urgent need. Several organic gold compounds were tested for activity against T. vaginalis thioredoxin reductase (TrxR) in cell-free systems as well as for activity against different trichomonads in vitro and in a murine infection model. The organic gold(I) compounds auranofin and chloro(diethylphenylphosphine)gold(I) inhibited TrxR in a concentration-dependent manner in assays with recombinant purified reductase and in cytoplasmic extracts of T. vaginalis transfected with a haemagglutinin epitope-tagged form of the reductase. Auranofin potently suppressed the growth of three independent clinical T. vaginalis isolates as well as several strains of another trichomonad (Tritrichomonas foetus) in a 24 h-assay, with 50% inhibitory concentrations of 0.7-2.5 µM and minimum lethal concentrations of 2-6 µM. The drug also compromised the ability of the parasite to overcome oxidant stress, supporting the notion that auranofin acts, in part, by inactivating TrxR-dependent antioxidant defences. Chloro(diethylphenylphosphine)gold(I) was 10-fold less effective against T. vaginalis in vitro than auranofin. Oral administration of auranofin for 4 days cleared the parasites in a murine model of vaginal T. foetus infection without displaying any apparent adverse effects. The approved human drug auranofin may be a promising agent as an alternative treatment of trichomoniasis in cases when standard nitro drug therapies have failed.

A guide to the rhomboid protein superfamily in development and disease

Rhomboid proteins are considered to be the most widespread membrane proteins across all forms of life. This superfamily comprises both active intramembrane serine proteases that catalyze the release of factors from the membrane, and a eukaryotic subset of non-catalytic members in which rhomboid architecture supports deviating functions. Although rhomboid was discovered in genetic studies of insect development, rhomboid research has broadened dramatically over the past 15 years; rhomboid enzymes are now the best biophysically understood of all intramembrane proteases, and are considered promising therapeutic targets for diseases ranging from parasitic infections to Parkinsonian neurodegeneration. Perhaps the most rapid progress has come with the catalytically inert rhomboid proteins, some of which regulate protein trafficking and/or function, and their prominence is underscored by clinical mutations. Such a diverse collection of advances mark an excellent point to review the state of this vibrant area of research, not because central questions have been answered, but instead because a firm grip in key areas has been established, and the field is now poised for breakthroughs.

Rhomboid protease inhibitors: Emerging tools and future therapeutics

Rhomboid-family intramembrane serine proteases are evolutionarily widespread. Their functions in different organisms are gradually being uncovered and already suggest medical relevance for infectious diseases and cancer. In contrast to these advances, selective inhibitors that could serve as efficient tools for investigation of physiological functions of rhomboids, validation of their disease relevance or as templates for drug development are lacking. In this review I extract what is known about rhomboid protease mechanism and specificity, examine the currently used inhibitors, their mechanism of action and limitations, and conclude by proposing routes for future development of rhomboid protease inhibitors.

Biology of rhomboid proteases in infectious diseases

Rhomboids are a well-conserved class of intramembrane serine proteases found in all kingdoms of life, sharing a conserved core structure of at least six transmembrane (TM) domains that contain the catalytic serine-histidine dyad. The rhomboid proteases, which cleave membrane embedded substrates within their TM domains, are emerging as an important group of enzymes controlling a myriad of biological processes. These enzymes are found in a wide variety of pathogens manifesting important roles in their pathological processes. Accordingly, they have received considerable attention as potential targets for pharmacological intervention over the past few years. This review provides a general update on rhomboid proteases and their roles in pathogenesis of human infectious agents.

Recent Advances in the Trichomonas vaginalis Field

The microaerophilic protist parasite Trichomonas vaginalis is occurring globally and causes infections in the urogenital tract in humans, a condition termed trichomoniasis. In fact, trichomoniasis is the most prevalent non-viral sexually transmitted disease with more than 250 million people infected every year. Although trichomoniasis is not life threatening in itself, it can be debilitating and increases the risk of adverse pregnancy outcomes, HIV infection, and, possibly, neoplasias in the prostate and the cervix. Apart from its role as a pathogen, T. vaginalis is also a fascinating organism with a surprisingly large genome for a parasite, i. e. larger than 160 Mb, and a physiology adapted to its microaerophilic lifestyle. In particular, the hydrogenosome, a mitochondria-derived organelle that produces hydrogen, has attracted much interest in the last few decades and rendered T. vaginalis a model organism for eukaryotic evolution. This review will give a succinct overview of the major advances in the T. vaginalis field in the last few years.