Ecotin, a microbial inhibitor of serine proteases, blocks multiple complement dependent and independent microbicidal activities of human serum

The ecotin-like peptidase inhibitor of Trypanosoma cruzi prevents TMPRSS2-PAR2-TLR4 crosstalk downmodulating infection and inflammation

Trypanosoma cruzi is the causative agent of Chagas disease, a chronic pathology that affects the heart and/or digestive system. This parasite invades and multiplies in virtually all nucleated cells, using a variety of host cell receptors for infection. T. cruzi has a gene that encodes an ecotin-like inhibitor of serine peptidases, ISP2. We generated ISP2-null mutants (Δisp2) in T. cruzi Dm28c using CRISPR/Cas9. Epimastigotes of Δisp2 grew normally in vitro but were more susceptible to lysis by human serum compared to parental and ISP2 add-back lines. Tissue culture trypomastigotes of Δisp2 were more infective to human muscle cells in vitro, which was reverted by the serine peptidase inhibitors aprotinin and camostat, suggesting that host cell epitheliasin/TMPRSS2 is the target of ISP2. Pretreatment of host cells with an antagonist to the protease-activated receptor 2 (PAR2) or an inhibitor of Toll-like receptor 4 (TLR4) selectively counteracted the increased cell invasion by Δisp2, but did not affect invasion by parental and add-back lines. The same was observed following targeted gene silencing of PAR2, TLR4 or TMPRSS2 in host cells by siRNA. Furthermore, Δisp2 caused increased tissue edema in a BALB/c mouse footpad infection model after 3 h differently to that observed following infection with parental and add-back lines. We propose that ISP2 contributes to protect T. cruzi from the anti-microbial effects of human serum and to prevent triggering of PAR2 and TLR4 in host cells, resulting in the modulation of host cell invasion and contributing to decrease inflammation during acute infection.

Transcriptional biomarker discovery toward building a load stress reporting system for engineered Escherichia coli strains

Foreign proteins are produced by introducing synthetic constructs into host bacteria for biotechnology applications. This process can cause resource competition between synthetic circuits and host cells, placing a metabolic burden on the host cells which may result in load stress and detrimental physiological changes. Consequently, the host bacteria can experience slow growth, and the synthetic system may suffer from suboptimal function. To help in the detection of bacterial load stress, we developed machine-learning strategies to select a minimal number of genes that could serve as biomarkers for the design of load stress reporters. We identified pairs of biomarkers that showed discriminative capacity to detect the load stress states induced in 41 engineered Escherichia coli strains.

Subversion of the Complement System by Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen heavily implicated in chronic diseases. Immunocompromised patients that become infected with P. aeruginosa usually are afflicted with a lifelong chronic infection, leading to worsened patient outcomes. The complement system is an integral piece of the first line of defense against invading microorganisms. Gram-negative bacteria are thought to be generally susceptible to attack from complement; however, P. aeruginosa can be an exception, with certain strains being serum resistant. Various molecular mechanisms have been described that confer P. aeruginosa unique resistance to numerous aspects of the complement response. In this review, we summarize the current published literature regarding the interactions of P. aeruginosa and complement, as well as the mechanisms used by P. aeruginosa to exploit various complement deficiencies and the strategies used to disrupt or hijack normal complement activities.

Shotgun Proteomics Analysis, Functional Networks, and Peptide Biomarkers for Seafood-Originating Biogenic-Amine-Producing Bacteria

Biogenic amine-producing bacteria are responsible for the production of basic nitrogenous compounds (histamine, cadaverine, tyramine, and putrescine) following the spoilage of food due to microorganisms. In this study, we adopted a shotgun proteomics strategy to characterize 15 foodborne strains of biogenic-amine-producing bacteria. A total of 10,673 peptide spectrum matches belonging to 4081 peptides and corresponding to 1811 proteins were identified. Relevant functional pathways were determined, and strains were differentiated into hierarchical clusters. An expected protein-protein interaction network was created (260 nodes/1973 interactions). Most of the determined proteins were associated with networks/pathways of energy, putrescine metabolism, and host-virus interaction. Additionally, 556 peptides were identified as virulence factors. Moreover, 77 species-specific peptide biomarkers corresponding to 64 different proteins were proposed to identify 10 bacterial species. This represents a major proteomic dataset of biogenic-amine-producing strains. These results may also be suitable for new treatments for food intoxication and for tracking microbial sources in foodstuffs.

Pseudomonas aeruginosa and the Complement System: A Review of the Evasion Strategies

The increasing emergence of multidrug resistant isolates of P. aeruginosa causes major problems in hospitals worldwide. This concern is particularly significant in bloodstream infections that progress rapidly, with a high number of deaths within the first hours and without time to select the most appropriate treatment. In fact, despite improvements in antimicrobial therapy and hospital care, P. aeruginosa bacteremia remains fatal in about 30% of cases. The complement system is a main defensive mechanism in blood against this pathogen. This system can mark bacteria for phagocytosis or directly lyse it via the insertion of a membrane attack complex in the bacterial membrane. P. aeruginosa exploits different strategies to resist complement attack. In this review for the special issue on “bacterial pathogens associated with bacteriemia”, we present an overview of the interactions between P. aeruginosa and the complement components and strategies used by this pathogen to prevent recognition and killing by the complement system. A thorough understanding of these interactions will be critical in order to develop drugs to counteract bacterial evasion mechanisms.

Tandem Multimerization Can Enhance the Structural Homogeneity and Antifungal Activity of the Silkworm Protease Inhibitor BmSPI39

Previous studies have shown that BmSPI39, a serine protease inhibitor of silkworm, can inhibit virulence-related proteases and the conidial germination of insect pathogenic fungi, thereby enhancing the antifungal capacity of Bombyx mori. The recombinant BmSPI39 expressed in Escherichia coli has poor structural homogeneity and is prone to spontaneous multimerization, which greatly limits its development and application. To date, the effect of multimerization on the inhibitory activity and antifungal ability of BmSPI39 remains unknown. It is urgent to explore whether a BmSPI39 tandem multimer with better structural homogeneity, higher activity and a stronger antifungal ability can be obtained by protein engineering. In this study, the expression vectors of BmSPI39 homotype tandem multimers were constructed using the isocaudomer method, and the recombinant proteins of tandem multimers were obtained by prokaryotic expression. The effects of BmSPI39 multimerization on its inhibitory activity and antifungal ability were investigated by protease inhibition and fungal growth inhibition experiments. In-gel activity staining and protease inhibition assays showed that tandem multimerization could not only greatly improve the structural homogeneity of the BmSPI39 protein, but also significantly increase its inhibitory activity against subtilisin and proteinase K. The results of conidial germination assays showed that tandem multimerization could effectively enhance the inhibitory ability of BmSPI39 on the conidial germination of Beauveria bassiana. A fungal growth inhibition assay showed that BmSPI39 tandem multimers had certain inhibitory effects on both Saccharomyces cerevisiae and Candida albicans. The inhibitory ability of BmSPI39 against these the above two fungi could be enhanced by tandem multimerization. In conclusion, this study successfully achieved the soluble expression of tandem multimers of the silkworm protease inhibitor BmSPI39 in E. coli and confirmed that tandem multimerization can improve the structural homogeneity and antifungal ability of BmSPI39. This study will not only help to deepen our understanding of the action mechanism of BmSPI39, but also provide an important theoretical basis and new strategy for cultivating antifungal transgenic silkworms. It will also promote its exogenous production and development and application in the medical field.

Ecotin: A versatile protease inhibitor of bacteria and eukaryotes

Serine protease inhibitors are a large family of proteins involved in important pathways and processes, such as inflammatory responses and blood clotting. Most are characterized by a precise mode of action, thereby targeting a narrow range of protease substrates. However, the serine-protease inhibitor ecotin is able to inhibit a broad range of serine proteases that display a wide range of specificities. This specificity is driven by special structural features which allow unique flexibility upon binding to targets. Although frequently observed in many human/animal-associated bacteria, ecotin homologs may also be found in plant-associated taxa and environmental species. The purpose of this review is to provide an update on the biological importance, role in host-microbe interactions, and evolutionary relationship between ecotin orthologs isolated from Eukaryotic and Prokaryotic species across the Tree of Life.

Pathogenicity and virulence of Burkholderia pseudomallei

The soil saprophyte, Burkholderia pseudomallei, is the causative agent of melioidosis, a disease endemic in South East Asia and northern Australia. Exposure to B. pseudomallei by either inhalation or inoculation can lead to severe disease. B. pseudomallei rapidly shifts from an environmental organism to an aggressive intracellular pathogen capable of rapidly spreading around the body. The expression of multiple virulence factors at every stage of intracellular infection allows for rapid progression of infection. Following invasion or phagocytosis, B. pseudomallei resists host-cell killing mechanisms in the phagosome, followed by escape using the type III secretion system. Several secreted virulence factors manipulate the host cell, while bacterial cells undergo a shift in energy metabolism allowing for overwhelming intracellular replication. Polymerisation of host cell actin into “actin tails” propels B. pseudomallei to the membranes of host cells where the type VI secretion system fuses host cells into multinucleated giant cells (MNGCs) to facilitate cell-to-cell dissemination. This review describes the various mechanisms used by B. pseudomallei to survive within cells.

Arg236 in human chymotrypsin B2 (CTRB2) is a key determinant of high enzyme activity, trypsinogen degradation capacity, and protection against pancreatitis

Pancreatic chymotrypsins (CTRs) are digestive proteases that in humans include CTRB1, CTRB2, CTRC, and CTRL. The highly similar CTRB1 and CTRB2 are the products of gene duplication. A common inversion at the CTRB1-CTRB2 locus reverses the expression ratio of these isoforms in favor of CTRB2. Carriers of the inversion allele are protected against the inflammatory disorder pancreatitis presumably via their increased capacity for CTRB2-mediated degradation of harmful trypsinogen. To reveal the protective molecular determinants of CTRB2, we compared enzymatic properties of CTRB1, CTRB2, and bovine CTRA (bCTRA). By evolving substrate-like Schistocerca gregaria proteinase inhibitor 2 (SGPI-2) inhibitory loop variants against the chymotrypsins, we found that the substrate binding groove of the three enzymes had overlapping specificities. Based on the selected sequences, we produced eight SGPI-2 variants. Remarkably, CTRB2 and bCTRA bound these inhibitors with significantly higher affinity than CTRB1. Moreover, digestion of peptide substrates, beta casein, and human anionic trypsinogen unequivocally confirmed that CTRB2 is a generally better enzyme than CTRB1 while the potency of bCTRA lies between those of the human isoforms. Unexpectedly, mutation D236R alone converted CTRB1 to a CTRB2-like high activity protease. Modeling indicated that in CTRB1 Met210 partially obstructed the substrate binding groove, which was relieved by the D236R mutation. Taken together, we identify CTRB2 Arg236 as a key positive determinant, while CTRB1 Asp236 as a negative determinant for chymotrypsin activity. These findings strongly support the concept that in carriers of the CTRB1-CTRB2 inversion allele, the superior trypsinogen degradation capacity of CTRB2 protects against pancreatitis.

Synergy of protease-binding sites within the ecotin homodimer is crucial for inhibition of MASP enzymes and for blocking lectin pathway activation

Ecotin is a homodimeric serine protease inhibitor produced by many commensal and pathogenic microbes. It functions as a virulence factor, enabling survival of various pathogens in the blood. The ecotin dimer binds two protease molecules, and each ecotin protomer has two protease-binding sites: site1 occupies the substrate-binding groove, whereas site2 engages a distinct secondary region. Owing to the twofold rotational symmetry within the ecotin dimer, sites 1 and 2 of a protomer bind to different protease molecules within the tetrameric complex. Escherichia coli ecotin inhibits trypsin-like, chymotrypsin-like, and elastase-like enzymes, including pancreatic proteases, leukocyte elastase, key enzymes of blood coagulation, the contact and complement systems, and other antimicrobial cascades. Here, we show that mannan-binding lectin-associated serine protease-1 (MASP-1) and MASP-2, essential activators of the complement lectin pathway, and MASP-3, an essential alternative pathway activator, are all inhibited by ecotin. We decipher in detail how the preorganization of site1 and site2 within the ecotin dimer contributes to the inhibition of each MASP enzyme. In addition, using mutated and monomeric ecotin variants, we show that site1, site2, and dimerization contribute to inhibition in a surprisingly target-dependent manner. We present the first ecotin:MASP-1 and ecotin:MASP-2 crystal structures, which provide additional insights and permit structural interpretation of the observed functional results. Importantly, we reveal that monomerization completely disables the MASP-2-inhibitory, MASP-3-inhibitory, and lectin pathway-inhibitory capacity of ecotin. These findings provide new opportunities to combat dangerous multidrug-resistant pathogens through development of compounds capable of blocking ecotin dimer formation.

Directed Evolution-Driven Increase of Structural Plasticity Is a Prerequisite for Binding the Complement Lectin Pathway Blocking MASP-Inhibitor Peptides

MASP-1 and MASP-2 are key activator proteases of the complement lectin pathway. The first specific mannose-binding lectin-associated serine protease (MASP) inhibitors had been developed from the 14-amino-acid sunflower trypsin inhibitor (SFTI) peptide by phage display, yielding SFTI-based MASP inhibitors, SFMIs. Here, we present the crystal structure of the MASP-1/SFMI1 complex that we analyzed in comparison to other existing MASP-1/2 structures. Rigidified backbone structure has long been accepted as a structural prerequisite for peptide inhibitors of proteases. We found that a hydrophobic cluster organized around the P2 Thr residue is essential for the structural stability of wild-type SFTI. We also found that the same P2 Thr prevents binding of the rigid SFTI-like peptides to the substrate-binding cleft of both MASPs as the cleft is partially blocked by large gatekeeper enzyme loops. Directed evolution removed this obstacle by replacing the P2 Thr with a Ser, providing the SFMIs with high-degree structural plasticity, which proved to be essential for MASP inhibition. To gain more insight into the structural criteria for SFMI-based MASP-2 inhibition, we systematically modified MASP-2-specific SFMI2 by capping its two termini and by replacing its disulfide bridge with varying length thioether linkers. By doing so, we also aimed to generate a versatile scaffold that is resistant to reducing environment and has increased stability in exopeptidase-containing biological environments. We found that the reduction-resistant disulfide-substituted l-2,3-diaminopropionic acid (Dap) variant possessed near-native potency. As MASP-2 is involved in the life-threatening thrombosis in COVID-19 patients, our synthetic, selective MASP-2 inhibitors could be relevant coronavirus drug candidates.

Lipoproteome screening of the Lyme disease agent identifies inhibitors of antibody-mediated complement killing

Spirochetal pathogens encode an abundance of lipoproteins that can provide a critical interface with the host environment. Borrelia burgdorferi, the model species for spirochetal biology, must survive an enzootic life cycle defined by fluctuations between vector (tick) and vertebrate host. While B. burgdorferi expresses over 80 surface lipoproteins—many of which likely contribute to host survival—the B. burgdorferi lipoproteome is poorly characterized. Here, we generated a platform to rapidly identify targets of B. burgdorferi surface lipoproteins and identified two paralogs that confer resistance to antibody-initiated complement killing that may promote survival in immunocompetent hosts. This work expands our understanding of complement evasion mechanisms and points toward a discovery approach for identifying host–pathogen interactions central to spirochete pathogenesis.

Spirochetal pathogens, such as the causative agent of Lyme disease, Borrelia burgdorferi sensu lato, encode an abundance of lipoproteins; however, due in part to their evolutionary distance from more well-studied bacteria, such as Proteobacteria and Firmicutes, few spirochetal lipoproteins have assigned functions. Indeed, B. burgdorferi devotes almost 8% of its genome to lipoprotein genes and interacts with its environment primarily through the production of at least 80 surface-exposed lipoproteins throughout its tick vector–vertebrate host lifecycle. Several B. burgdorferi lipoproteins have been shown to serve roles in cellular adherence or immune evasion, but the functions for most B. burgdorferi surface lipoproteins remain unknown. In this study, we developed a B. burgdorferi lipoproteome screening platform utilizing intact spirochetes that enables the identification of previously unrecognized host interactions. As spirochetal survival in the bloodstream is essential for dissemination, we targeted our screen to C1, the first component of the classical (antibody-initiated) complement pathway. We identified two high-affinity C1 interactions by the paralogous lipoproteins, ElpB and ElpQ (also termed ErpB and ErpQ, respectively). Using biochemical, microbiological, and biophysical approaches, we demonstrate that ElpB and ElpQ bind the activated forms of the C1 proteases, C1r and C1s, and represent a distinct mechanistic class of C1 inhibitors that protect the spirochete from antibody-mediated complement killing. In addition to identifying a mode of complement inhibition, our study establishes a lipoproteome screening methodology as a discovery platform for identifying direct host–pathogen interactions that are central to the pathogenesis of spirochetes, such as the Lyme disease agent.

Characterization of Differentially Abundant Proteins Among Leishmania (Viannia) braziliensis Strains Isolated From Atypical or Typical Lesions

Leishmania (Viannia) braziliensis is the main etiological agent of cutaneous and mucocutaneous leishmaniasis in Latin America. Non-ulcerated atypical tegumentary leishmaniasis cases caused by L. braziliensis have been reported in several regions of the American continent, including the Xacriabá indigenous reserve in São João das Missões/Minas Gerais, Brazil. Parasites isolated from these atypical clinical lesions are resistant to antimony-based therapeutics. In the present study, proteins displaying differential abundance in two strains of L. braziliensis isolated from patients with atypical lesions compared with four strains isolated from patients with typical lesions were identified using a quantitative proteomics approach based on tandem mass tag labeling (TMT) and mass spectrometry. A total of 532 (P<0.05) differentially abundant proteins were identified (298 upregulated and 234 downregulated) in strains from atypical lesions compared to strains from typical lesions. Prominent positively regulated proteins in atypical strains included those that may confer greater survival inside macrophages, proteins related to antimony resistance, and proteins associated with higher peroxidase activity. Additionally, we identified proteins showing potential as new drug and vaccine targets. Our findings contribute to the characterization of these intriguing L. braziliensis strains and provide a novel perspective on Atypical Cutaneous Leishmaniasis (ACL) cases that have been associated with therapeutic failures.

Whole-genome sequence-informed MALDI-TOF MS diagnostics reveal importance of Klebsiella oxytoca group in invasive infections: a retrospective clinical study

BACKGROUND

Klebsiella spp. are opportunistic pathogens which can cause severe infections, are often multi-drug resistant and are a common cause of hospital-acquired infections. Multiple new Klebsiella species have recently been described, yet their clinical impact and antibiotic resistance profiles are largely unknown. We aimed to explore Klebsiella group- and species-specific clinical impact, antimicrobial resistance (AMR) and virulence.

METHODS

We analysed whole-genome sequence data of a diverse selection of Klebsiella spp. isolates and identified resistance and virulence factors. Using the genomes of 3594 Klebsiella isolates, we predicted the masses of 56 ribosomal subunit proteins and identified species-specific marker masses. We then re-analysed over 22,000 Matrix-Assisted Laser Desorption Ionization - Time Of Flight (MALDI-TOF) mass spectra routinely acquired at eight healthcare institutions in four countries looking for these species-specific markers. Analyses of clinical and microbiological endpoints from a subset of 957 patients with infections from Klebsiella species were performed using generalized linear mixed-effects models.

RESULTS

Our comparative genomic analysis shows group- and species-specific trends in accessory genome composition. With the identified species-specific marker masses, eight Klebsiella species can be distinguished using MALDI-TOF MS. We identified K. pneumoniae (71.2%; n = 12,523), K. quasipneumoniae (3.3%; n = 575), K. variicola (9.8%; n = 1717), "K. quasivariicola" (0.3%; n = 52), K. oxytoca (8.2%; n = 1445), K. michiganensis (4.8%; n = 836), K. grimontii (2.4%; n = 425) and K. huaxensis (0.1%; n = 12). Isolates belonging to the K. oxytoca group, which includes the species K. oxytoca, K. michiganensis and K. grimontii, were less often resistant to 4th-generation cephalosporins than isolates of the K. pneumoniae group, which includes the species K. pneumoniae, K. quasipneumoniae, K. variicola and "K. quasivariicola" (odds ratio = 0.17, p < 0.001, 95% confidence interval [0.09,0.28]). Within the K. pneumoniae group, isolates identified as K. pneumoniae were more often resistant to 4th-generation cephalosporins than K. variicola isolates (odds ratio = 2.61, p = 0.003, 95% confidence interval [1.38,5.06]). K. oxytoca group isolates were found to be more likely associated with invasive infection to primary sterile sites than K. pneumoniae group isolates (odds ratio = 2.39, p = 0.0044, 95% confidence interval [1.05,5.53]).

CONCLUSIONS

Currently misdiagnosed Klebsiella spp. can be distinguished using a ribosomal marker-based approach for MALDI-TOF MS. Klebsiella groups and species differed in AMR profiles, and in their association with invasive infection, highlighting the importance for species identification to enable effective treatment options.

The relationship between gut microbiota and proteolytic activity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease that affects 3.8-9.2% of the world population. It affects the physiology and psychology of patients and increases the burden on families, the healthcare system, society, and economic development. Presently, a large number of studies have shown that compared to healthy individuals, the composition and diversity of gut microbiota in IBS patients have changed, and the proteolytic activity (PA) in fecal supernatant and colonic mucosa of IBS patients has also increased. These findings indicate that the imbalance of intestinal microecology and intestinal protein hydrolysis is closely related to IBS. Furthermore, the intestinal flora is a key substance that regulates the PA and is associated with IBS. The current review described the intestinal microecology and intestinal proteolytic activity of patients with IBS and also discussed the effect of intestinal flora on PA. In summary, this study proposed a pivotal role of gut microbiota and PA in IBS, respectively, and provided an in-depth insight into the diagnosis and treatment targets of IBS as well as the formulation of new treatment strategies for other digestive diseases and protease-related diseases.

Host immune response against leishmaniasis and parasite persistence strategies: A review and assessment of recent research

Leishmaniasis, a neglected parasitic disease caused by a unicellular protozoan of the genus Leishmania, is transmitted through the bite of a female sandfly. The disease remains a major public health problem and is linked to tropical and subtropical regions, with an endemic picture in several regions, including East Africa, the Mediterranean basin and South America. The different causative species display a diversity of clinical presentations; therefore, the immunological data on leishmaniasis are both scarce and controversial for the different forms and infecting species of the parasite. The present review highlights the main immune parameters associated with leishmaniasis that might contribute to a better understanding of the pathogenicity of the parasite and the clinical outcomes of the disease. Our aim was to provide a concise overview of the immunobiology of the disease and the factors that influence it, as this knowledge may be helpful in developing novel chemotherapeutic and vaccine strategies.

Ecotin and LamB in Escherichia coli influence the susceptibility to Type VI secretion-mediated interbacterial competition and killing by Vibrio cholerae

BACKGROUND

A prevailing action of the Type VI secretion system (T6SS) in several Gram-negative bacterial species is inter-bacterial competition. In the past several years, many effectors of T6SS were identified in different bacterial species and their involvement in inter-bacterial interactions were described. However, possible defence mechanisms against T6SS attack among prey bacteria were not well clarified yet.

METHODS

Escherichia coli was assessed for susceptibility to T6SS-mediated killing by Vibrio cholerae. TheT6SS-mediated bacterial killing assays were performed in absence or presence of different protease inhibitors and with different mutant E. coli strains. Expression levels of selected proteins were monitored using SDS-PAGE and immunoblot analyses.

RESULTS

The T6SS-mediated killing of E. coli by V. cholerae was partly blocked when the serine protease inhibitor Pefabloc was present. E. coli lacking the periplasmic protease inhibitor Ecotin showed enhanced susceptibility to killing by V. cholerae. Mutations affecting E. coli membrane stability also caused increased susceptibility to killing by V. cholerae. E. coli lacking the maltodextrin porin protein LamB showed reduced susceptibility to killing by V. cholerae whereas E. coli with induced high levels of LamB showed reduced survival in inter-bacterial competition.

CONCLUSIONS

Our study identified two proteins in E. coli, the intrinsic protease inhibitor Ecotin and the outer membrane porin LamB, that influenced E. coli susceptibility to T6SS-mediated killing by V. cholerae.

GENERAL SIGNIFICANCE

We envision that it is feasible to explore these findings to target and modulate their expression to obtain desired changes in inter-bacterial competition in vivo, e.g. in the gastrointestinal microbiome.

Characterization of ecotin homologs from Campylobacter rectus and Campylobacter showae

Ecotin, first described in Escherichia coli, is a potent inhibitor of a broad range of serine proteases including those typically released by the innate immune system such as neutrophil elastase (NE). Here we describe the identification of ecotin orthologs in various Campylobacter species, including Campylobacter rectus and Campylobacter showae residing in the oral cavity and implicated in the development and progression of periodontal disease in humans. To investigate the function of these ecotins in vitro, the orthologs from C. rectus and C. showae were recombinantly expressed and purified from E. coli. Using CmeA degradation/protection assays, fluorescence resonance energy transfer and NE activity assays, we found that ecotins from C. rectus and C. showae inhibit NE, factor Xa and trypsin, but not the Campylobacter jejuni serine protease HtrA or its ortholog in E. coli, DegP. To further evaluate ecotin function in vivo, an E. coli ecotin-deficient mutant was complemented with the C. rectus and C. showae homologs. Using a neutrophil killing assay, we demonstrate that the low survival rate of the E. coli ecotin-deficient mutant can be rescued upon expression of ecotins from C. rectus and C. showae. In addition, the C. rectus and C. showae ecotins partially compensate for loss of N-glycosylation and increased protease susceptibility in the related pathogen, Campylobacter jejuni, thus implicating a similar role for these proteins in the native host to cope with the protease-rich environment of the oral cavity.

Structural Basis for the Inhibition Mechanism of Ecotin against Neutrophil Elastase by Targeting the Active Site and Secondary Binding Site

Human neutrophil elastase (hNE) is a serine protease that plays a major role in defending the bacterial infection. However, elevated expression of hNE is reported in lung and breast cancer, among others. Moreover, hNE is a target for the treatment of cardiopulmonary diseases. Ecotin (ET) is a serine protease inhibitor present in many Gram-negative bacteria, and it plays a physiological role in inhibiting host proteases, including hNE. Despite this known interaction, the structure of the hNE-ET complex has not been reported, and the mechanism of ecotin inhibition is not available. We determined the structure of the hNE-ET complex by molecular replacement method. The structure of the hNE-ET complex revealed the presence of six interface regions comprising 50s, 60s, and 80s loops, between the ET dimer and two independent hNE monomers, which explains the high affinity of ecotin for hNE (12 pM). Notably, we observed a secondary binding site of hNE located 24 Å from the primary binding site. Comparison of the closely related trypsin-ecotin complex with our hNE-ET complex shows movement of the backbone atoms of the 80s and 50s loops by 4.6 Å, suggesting the flexibility of these loops in inhibiting a range of proteases. Through a detailed structural analysis, we demonstrate the flexibility of the hNE subsites to dock various side chains concomitant with inhibition, indicating the broad specificity of hNE against various inhibitors. These findings will aid in the design of chimeric inhibitors that target both sites of hNE and in the development of therapeutics for controlling hNE-mediated pathogenesis.

Functional and structural characterization of an ecotin-like serine protease inhibitor from Trypanosoma cruzi

Ecotin, a serine peptidase inhibitor (ISP), discovered in Escherichia coli, inhibit a wide range of trypsin-like serine peptidases, protecting microorganisms from the host's immune response. In eukaryotes, ISPs encoding genes were found only in Trypanosomatidae protozoa, including the genus Trypanosoma, which harbors Trypanosoma cruzi, the ethiological agent of Chagas' disease. T. cruzi encodes the ISP2 Trypanosomatidae orthologous, which in Leishmania species present inhibitory activity on mammalian proteases from S1A family suggesting its role in vertebrate-host-parasite interactions. In this study, the structural and biochemical characterization of the recombinant T. cruzi ISP2 (rTcISP2), produced in E. coli was purified in soluble form and analyzed by circular dichroism, fluorescence spectroscopy, native electrophoresis, dynamic light scattering, low X-ray scattering and homology modeling. The obtained data revealed that rTcISP2 was biologically active and forms homodimers in solution. Furthermore, inhibitory activity of rTcISP2 against human neutrophil elastase (HNE) is the highest among ISP2 orthologous from bacteria and trypanosomatids. The role of NE to control T. cruzi parasites through modulation of cellular and humoral innate immune responses in vertebrate hosts, make TcISP2 a key molecular component for parasite infection efficiency, providing a useful basis for investigation of host-parasite interactions and the potential of TcISP2 for biotechnological applications.