Generation of active fragments from human zymogens in the brady kinin-generating cascade by extracellular proteases from Vibrio vulnificus and V. parahaemolyticus

MARTX toxin of Vibrio vulnificus induces RBC phosphatidylserine exposure that can contribute to thrombosis

V. vulnificus-infected patients suffer from hemolytic anemia and circulatory lesions, often accompanied by venous thrombosis. However, the pathophysiological mechanism of venous thrombosis associated with V. vulnificus infection remains largely unknown. Herein, V. vulnificus infection at the sub-hemolytic level induced shape change of human red blood cells (RBCs) accompanied by phosphatidylserine exposure, and microvesicle generation, leading to the procoagulant activation of RBCs and ultimately, acquisition of prothrombotic activity. Of note, V. vulnificus exposed to RBCs substantially upregulated the rtxA gene encoding multifunctional autoprocessing repeats-in-toxin (MARTX) toxin. Mutant studies showed that V. vulnificus-induced RBC procoagulant activity was due to the pore forming region of the MARTX toxin causing intracellular Ca²⁺ influx in RBCs. In a rat venous thrombosis model triggered by tissue factor and stasis, the V. vulnificus wild type increased thrombosis while the ΔrtxA mutant failed to increase thrombosis, confirming that V. vulnificus induces thrombosis through the procoagulant activation of RBCs via the mediation of the MARTX toxin.

The pathophysiological mechanism of venous thrombosis associated with Vibrio vulnificus infection remains largely unknown. In this work, the authors investigate this association, focusing on effects of the pore-forming MARTX toxin of V. vulnificus on red blood cells, and the utilisation of a rat venous thrombosis model.

Dissecting capture and twisting of aureolysin and pseudolysin: functional amino acids of the Dispase autolysis-inducing protein

The Dispase autolysis-inducing protein (DAIP) from Streptomyces mobaraensis attracts M4 metalloproteases, which results in inhibition and autolysis of bacillolysin (BL) and thermolysin (TL). The present study shows that aureolysin (AL) from Staphylococcus aureus and pseudolysin (LasB) from Pseudomonas aeruginosa are likewise impaired by DAIP. Complete inhibition occurred when DAIP significantly exceeded the amount of the target protease. At low DAIP concentrations, AL and BL performed autolysis, while LasB and TL degradation required reductants or detergents that break intramolecular disulfide bonds or change the protein structure. Site directed mutagenesis of DAIP and removal of an exposed protein loop either influenced binding or inhibition of AL and TL but had no effect on LasB and BL. The Y170A and Δ239-248 variants had completely lost affinity for TL and AL. The exchange of Asn-275 also impaired the interaction of DAIP with AL. In contrast, DAIP Phe-297 substitution abolished inhibition and autolysis of both target proteases but still allowed complex formation. Our results give rise to the conclusion that other, yet unknown DAIP amino acids inactivate LasB and BL. Obviously, various bacteria in the same habitat caused Streptomyces mobaraensis to continuously optimize DAIP in inactivating the tackling metalloproteases.

Functional analysis of N-terminal propeptide in the precursor of Vibrio vulnificus metalloprotease by using cell-free translational system

Vibrio vulnificus is a human pathogen causing fatal septicemia with edematous and hemorrhagic skin damage. Among multiple virulence factors, an extracellular metalloprotease termed as V. vulnificus protease (VVP) is known to play a crucial role in eliciting the skin damage. The mature VVP (413 aa) is composed of two domains, the N-terminal core domain with proteolytic activity and the C-terminal domain mediates efficient attachment to protein substrates. However, VVP is produced as an inactive precursor (609 aa) with a signal peptide (24 aa) and propeptide (172 aa). In order to clarify the function of propeptide, a series of DNA fragments encoding the VVP precursor and its various domains were designed and the proteins were expressed in vitro by using cell-free translational system. The results indicated that the propeptide might function as an intramolecular chaperon to promote the proper folding of both N-terminal and C-terminal domains. The obtained results also suggest that the propeptide, itself was unstable and thus digested easily by the enzymes present in cell lysate used for cell-free system. Additionally, the C-terminal domain in VVP found to inhibit the folding of the N-terminal domain in absence of propeptide.

Interaction of the Human Contact System with Pathogens-An Update

The name human contact system is related to its mode of action, as "contact" with artificial negatively charged surfaces triggers its activation. Today, it is generally believed that the contact system is an inflammatory response mechanism not only against artificial material but also against misfolded proteins and foreign organisms. Upon activation, the contact system is involved in at least two distinct (patho)physiologic processes:i. the trigger of the intrinsic coagulation via factor XI and ii. the cleavage of high molecular weight kininogen with release of bradykinin and antimicrobial peptides (AMPs). Bradykinin is involved in the regulation of inflammatory processes, vascular permeability, and blood pressure. Due to the release of AMPs, the contact system is regarded as a branch of the innate immune defense against microorganisms. There is an increasing list of pathogens that interact with contact factors, in addition to bacteria also fungi and viruses bind and activate the system. In spite of that, pathogens have developed their own mechanisms to activate the contact system, resulting in manipulation of this host immune response. In this up-to-date review, we summarize present research on the interaction of pathogens with the human contact system, focusing particularly on bacterial and viral mechanisms that trigger inflammation via contact system activation.

Role of the Histone-Like Nucleoid Structuring Protein (H-NS) in the Regulation of Virulence Factor Expression and Stress Response in Vibrio vulnificus

Temperature is one of the important parameters regulating the expression of virulence factors in bacteria. The global regulator, a histone-like nucleoid structuring protein (H-NS), is known to play a crucial role in this regulation. In the present study, we first clarified the role of H-NS in the temperature-dependent regulation of virulence factor production in Vibrio vulnificus, including that of the cytolytic toxin (V. vulnificus hemolysin: VVH) and the proteolytic enzyme (V. vulnificus protease: VVP). The expression of hns itself was subjected to temperature regulation, where hns was expressed more at 26 ℃ than at 37 ℃. VVH production and the expression of its gene vvhA were increased by disruption of the hns gene. H-NS appeared to affect the vvhA expression by the well-documented transcriptional silencing mechanism. On the other hand, hns disruption resulted in the reduction of VVP production and the expression of its gene vvpE. H-NS was suggested to positively regulate vvpE expression through the increase in the level of the rpoS mRNA. Moreover, H-NS was found to contribute to the survival of V. vulnificus in stressful environments. When compared to the wild type strain, the hns mutant exhibited reduced survival rates when subjected to acidic pH, hyperosmotic and oxidative stress.

Stationary-phase induction of vvpS expression by three transcription factors: repression by LeuO and activation by SmcR and CRP

An exoprotease of Vibrio vulnificus, VvpS, exhibits an autolytic function during the stationary phase. To understand how vvpS expression is controlled, the regulators involved in vvpS transcription and their regulatory mechanisms were investigated. LeuO was isolated in a ligand-fishing experiment, and experiments using a leuO-deletion mutant revealed that LeuO represses vvpS transcription. LeuO bound the extended region including LeuO-binding site (LBS)-I and LBS-II. Further screening of additional regulators revealed that SmcR and cyclic adenosine monophosphate-receptor protein (CRP) play activating roles in vvpS transcription. SmcR and CRP bound the regions overlapping LBS-I and -II, respectively. In addition, the LeuO occupancy of LBS-I and LBS-II was competitively exchanged by SmcR and CRP, respectively. To examine the mechanism of stationary-phase induction of vvpS expression, in vivo levels of three transcription factors were monitored. Cellular level of LeuO was maximal at exponential phase, while those of SmcR and CRP were maximal at stationary phase and relatively constant after the early-exponential phase, respectively. Thus, vvpS transcription was not induced during the exponential phase by high cellular content of LeuO. When entering the stationary phase, however, LeuO content was significantly reduced and repression by LeuO was relieved through simultaneous binding of SmcR and CRP to LBS-I and -II, respectively.

Extracellular proteolytic enzymes produced by human pathogenic vibrio species

Bacteria in the genus Vibrio produce extracellular proteolytic enzymes to obtain nutrients via digestion of various protein substrates. However, the enzymes secreted by human pathogenic species have been documented to modulate the bacterial virulence. Several species including Vibrio cholerae and V. vulnificus are known to produce thermolysin-like metalloproteases termed vibriolysin. The vibriolysin from V. vulnificus, a causative agent of serious systemic infection, is a major toxic factor eliciting the secondary skin damage characterized by formation of the hemorrhagic brae. The vibriolysin from intestinal pathogens may play indirect roles in pathogenicity because it can activate protein toxins and hemagglutinin by the limited proteolysis and can affect the bacterial attachment to or detachment from the intestinal surface by degradation of the mucus layer. Two species causing wound infections, V. alginolyticus and V. parahaemolyticus, produce another metalloproteases so-called collagenases. Although the detailed pathological roles have not been studied, the collagenase is potent to accelerate the bacterial dissemination through digestion of the protein components of the extracellular matrix. Some species produce cymotrypsin-like serine proteases, which may also affect the bacterial virulence potential. The intestinal pathogens produce sufficient amounts of the metalloprotease at the small intestinal temperature; however, the metalloprotease production by extra-intestinal pathogens is much higher around the body surface temperature. On the other hand, the serine protease is expressed only in the absence of the metalloprotease.

Crosstalk of the plasma contact system with bacteria

Activation of the plasma contact system triggers several cascade systems such as the kallikrein-kinin system, the intrinsic pathway of coagulation, the classical complement cascade and the fibrinolytic system. Recent studies have shown a critical role of the contact system for arterial and venous thrombus formation and thromboembolic disease. In contrast, the function of the contact system for host-defense reactions and its physiological functions have remained enigmatic. Experimental animal studies and clinical data have linked the contact system to bacterial infections with implications for sepsis disease. The present review summarizes the role of the contact system and its activation for bacterial infections.

The enhanced permeability retention effect: a new paradigm for drug targeting in infection

Multidrug-resistant, Gram-negative infection is a major global determinant of morbidity, mortality and cost of care. The advent of nanomedicine has enabled tailored engineering of macromolecular constructs, permitting increasingly selective targeting, alteration of volume of distribution and activity/toxicity. Macromolecules tend to passively and preferentially accumulate at sites of enhanced vascular permeability and are then retained. This enhanced permeability and retention (EPR) effect, whilst recognized as a major breakthrough in anti-tumoral targeting, has not yet been fully exploited in infection. Shared pathophysiological pathways in both cancer and infection are evident and a number of novel nanomedicines have shown promise in selective, passive, size-mediated targeting to infection. This review describes the similarities and parallels in pathophysiological pathways at molecular, cellular and circulatory levels between inflammation/infection and cancer therapy, where use of this principle has been established.

Proteases produced by vibrios

Bacteria of the genus Vibrio are normal habitants of the aquatic environment but the some species are believed to be human pathogens. Pathogenic vibrios produce various pathogenic factors, and the proteases are also recognized to play pathogenic roles in the infection: the direct roles by digesting many kinds of host proteins or indirect roles by processing other pathogenic protein factors. Especially VVP from Vibrio vulnificus is thought to be a major pathogenic factor of the vibrio. Although HA/P, the V. cholerae hemagglutinin/protease, is not a direct toxic factor of cholera vibrio, its significance is an undeniable fact. Production of HA/P is regulated together with major pathogenic factors such as CT (cholera toxin) or TCP (toxin co-regulated pilus) by a quorum-sensing system. HA/P is necessary for full expression of pathogenicity of the vibrio by supporting growth and translocation in the digestive tract. Processing of protein toxins such as CT or El Tor hemolysin is also an important pathogenic role.

Degradation of human kininogens with the release of kinin peptides by extracellular proteinases of Candida spp

The secretion of proteolytic enzymes by pathogenic microorganisms is one of the most successful strategies used by pathogens to colonize and infect the host organism. The extracellular microbial proteinases can seriously deregulate the homeostatic proteolytic cascades of the host, including the kinin-forming system, repeatedly reported to be activated during bacterial infection. The current study assigns a kinin-releasing activity to secreted proteinases of Candida spp. yeasts, the major fungal pathogens of humans. Of several Candida species studied, C. parapsilosis and C. albicans in their invasive filamentous forms are shown to produce proteinases which most effectively degrade proteinaceous kinin precursors, the kininogens. These enzymes, classified as aspartyl proteinases, have the highest kininogen-degrading activity at low pH (approx. 3.5), but the associated production of bradykinin-related peptides from a small fraction of kininogen molecules is optimal at neutral pH (6.5). The peptides effectively interact with cellular B2-type kinin receptors. Moreover, kinin-related peptides capable of interacting with inflammation-induced B1-type receptors are also formed, but with a reversed pH dependence. The presented variability of the potential extracellular kinin production by secreted aspartyl proteinases of Candida spp. is consistent with the known adaptability of these opportunistic pathogens to different niches in the host organism.

Adsorption of components of the plasma kinin-forming system on the surface of Porphyromonas gingivalis involves gingipains as the major docking platforms

Enhanced production of proinflammatory bradykinin-related peptides, the kinins, has been suggested to contribute to the pathogenesis of periodontitis, a common inflammatory disease of human gingival tissues. In this report, we describe a plausible mechanism of activation of the kinin-generating system, also known as the contact system or kininogen-kallikrein-kinin system, by the adsorption of its plasma-derived components such as high-molecular-mass kininogen (HK), prekallikrein (PK), and Hageman factor (FXII) to the cell surface of periodontal pathogen Porphyromonas gingivalis. The adsorption characteristics of mutant strains deficient in selected proteins of the cell envelope suggested that the surface-associated cysteine proteinases, gingipains, bearing hemagglutinin/adhesin domains (RgpA and Kgp) serve as the major platforms for HK and FXII adhesion. These interactions were confirmed by direct binding tests using microplate-immobilized gingipains and biotinylated contact factors. Other bacterial cell surface components such as fimbriae and lipopolysaccharide were also found to contribute to the binding of contact factors, particularly PK. Analysis of kinin release in plasma upon contact with P. gingivalis showed that the bacterial surface-dependent mechanism is complementary to the previously described kinin generation system dependent on HK and PK proteolytic activation by the gingipains. We also found that several P. gingivalis clinical isolates differed in the relative significance of these two mechanisms of kinin production. Taken together, these data show the importance of this specific type of bacterial surface-host homeostatic system interaction in periodontal infections.

A recombinant metalloprotease antigen of Vibrio vulnificus elicits protective antibodies in a murine model

AIMS

To investigate whether Vibrio vulnificus metalloprotease (VvpE) can induce the production of specific anti-VvpE antibody to confer effective protection against Vibrio vulnificus infection and to evaluate the possibility of VvpE as a potential vaccine candidate against disease caused by V. vulnificus.

METHODS AND RESULTS

The gene encoding the 65-kDa VvpE of V. vulnificus was amplified by PCR and cloned into the expression vector pET21(b). The recombinant VvpE of V. vulnificus was expressed in Escherichia coli BL21(DE3). This His(6)-tagged VvpE was purified and injected intramuscularly into mice to evaluate its ability to stimulate immune response. Specific antibody levels were measured by ELISA. The 75% protective efficacy of recombinant VvpE was evaluated by active immunization and intraperitoneal challenge with V. vulnificus in mice.

CONCLUSIONS

The recombinant His(6)-tagged VvpE of V. vulnificus is capable of inducing high antibody response in mice to confer effective protection against lethal challenge with V. vulnificus. VvpE might be a potential vaccine candidate to against V. vulnificus infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study uses His(6)-tagged VvpE to act as vaccine that successfully induces effective and specific anti-VvpE antibody and offers an option for the potential vaccine candidate against V. vulnificus infection.

The Role of Neuropeptide Endopeptidases in Cutaneous Immunity

Proteolytic processing and degradation plays an important role in modulating the generation and bioactivity of neuroendocrine peptide mediators, a class of key molecules in cutaneous biology.

Accordingly, the cellular localization and expression, and the molecular biology and structural properties of selected intracellular prohormone convertases and ectopically expressed zinc-binding metalloendoproteases are discussed.

A special reference will be made to the physiologic and pathophysiologic significance of these endopeptidases in cutaneous immunobiology.

Because of the number of pathologically relevant changes in inflammation and tumor progression that can be directly attributed to neprilysin and angiotensin-converting enzyme, a particular focus will be on the role of these enzymes in modulating innate and adaptive immune responses in the skin.

Induction of vascular leakage and blood pressure lowering through kinin release by a serine proteinase from Aeromonas sobria

Aeromonas sobria causes septic shock, a condition associated with high mortality. To study the mechanism of septic shock by A. sobria infection, we examined the vascular leakage (VL) activity of A. sobria serine proteinase (ASP), a serine proteinase secreted by this pathogen. Proteolytically active ASP induced VL mainly in a bradykinin (BK) B(2) receptor-, and partially in a histamine-H(1) receptor-dependent manner in guinea pig skin. The ASP VL activity peaked at 10 min to 1.8-fold of the initial activity with an increased BK B(2) receptor dependency, and attenuated almost completely within 30 min. ASP produced VL activity from human plasma apparently through kallikrein/kinin system activation, suggesting that ASP can generate kinin in humans. Consistent with the finding that a major part of the ASP-induced VL was reduced by a potent kallikrein inhibitor, soybean trypsin inhibitor that does not affect ASP enzymatic activity, ASP activated prekallikrein but not factor XII to generate kallikrein in a dose- and incubation time-dependent manner. ASP produced more VL activity directly from human low m.w. kininogen than high m.w. kininogen when both were used at their normal plasma concentrations. Intra-arterial injection of ASP into guinea pigs lowered blood pressure specifically via the BK B(2) receptor. These data suggest that ASP induces VL through prekallikrein activation and direct kinin release from kininogens, which is a previously undescribed mechanism of A. sobria virulence and could be associated with the induction of septic shock by infection with this bacterium. ASP-specific inhibitors, and kinin receptor antagonists, might prove useful for the treatment or prevention of this fatal disease.

Vibrio vulnificus infection and metalloprotease

Vibrio vulnificus is ubiquitous in aquatic environments; however, it occasionally causes serious and often fatal infections in humans. These include invasive septicemia contracted through consumption of raw seafood, as well as wound infections acquired through contact with brackish or marine waters. In most cases of septicemia, the patients have underlying disease(s), such as liver dysfunction or alcoholic cirrhosis, and the secondary skin lesions including cellulitis, edema and hemorrhagic bulla appear on the limbs. Although V. Vul produces various virulent factors including polysaccharide capsule, type IV pili, hemolysin and proteolytic enzymes, the 45-kDa metalloprotease may be a causative factor of the skin lesions, because the purified protease enhances vascular permeability through generation of chemical mediators and also induces serious hemorrhagic damage through digestion of the vascular basement membrane. As well as other bacteria, V. Vul can regulate the protease production through the quorum-sensing system depending on bacterial cell density. However, this system operates efficiently at 25 degrees C, but not at 37 degrees C. Therefore, V. vulnificus may produce sufficient amounts of the protease only in the interstitial tissue of the limbs, in which temperature is lower than the internal temperature of the human body.

Pathogenic Factors of Vibrios with Special Emphasis on Vibrio vulnificus

Bacteria of the genus Vibrio are normal habitants of the aquatic environment and play roles for biocontrole of aquatic ecosystem, but some species are believed to be human pathogens. These species can be classified into two groups according to the types of diseases they cause: the gastrointestinal infections and the extraintestinal infections. The pathogenic species produce various pathogenic factors including enterotoxin, hemolysin, cytotoxin, protease, siderophore, adhesive factor, and hemagglutinin. We studied various pathogenic factors of vibrios with special emphasis on protease and hemolysin of V. vulnificus. V. vulnificus is now recognized as being among the most rapidly fatal of human pathogens, although the infection is appeared in patients having underlying disease(s) such as liver dysfunction, alcoholic cirrhosis or haemochromatosis. V. vulnificus protease (VVP) is thought to be a major toxic factor causing skin damage in the patients having septicemia. VVP is a metalloprotease and degrades a number of biologically important proteins including elastin, fibrinogen, and plasma proteinase inhibitors of complement components. VVP causes skin damages through activation of the Factor XII-plasma kallikrein-kinin cascade and/or exocytotic histamine release from mast cells, and a haemorrhagic lesion through digestion of the vascular basement membrane. Thus, the protease is the most probable candidate for tissue damage and bacterial invasion during an infection. Pathogenic roles and functional mechanism of other factors including hemolysins of V. vulnificus and V. mimicus are also shown in this review article.