The C-terminal domain promotes the hemorrhagic damage caused by Vibrio vulnificus metalloprotease

In-hospital mortality associated with necrotizing soft tissue infection due to Vibrio vulnificus: a matched-pair cohort study

Background

It remains unclear whether Vibrio vulnificus necrotizing soft tissue infection (NSTI) is associated with higher mortality compared with non-Vibrio NSTI. This study’s objective was to compare outcomes including in-hospital mortality and prognosis between patients with V. vulnificus NSTI and those with non-Vibrio NSTI.

Method

A retrospective 1:2 matched-pair cohort study of hospitalized patients with NSTI diagnosed by surgical finding was conducted in two tertiary hospitals in southern Taiwan between January 2015 and January 2020. In-hospital outcomes (mortality, length of stay) were compared between patients with and without V. vulnificus infection. We performed multiple imputation using chained equations followed by multivariable regression analyses fitted with generalized estimating equations to account for clustering within matched pairs. All-cause in-hospital mortality and length of stay during hospitalization were compared for NSTI patients with and without V. vulnificus.

Result

A total of 135 patients were included, 45 in V. vulnificus NSTI group and 90 in non-Vibrio group. The V. vulnificus NSTI patients had higher mortality and longer hospital stays. Multivariable logistic regression analysis revealed that V. vulnificus NSTI was significantly associated with higher in-hospital mortality compared with non-Vibrio NSTI (adjusted odds ratio = 1.52; 95% confidence interval 1.36–1.70; p < 0.01).

Conclusion

Vibrio vulnificus NSTI was associated with higher in-hospital mortality and longer hospital stay which may increase health care costs, suggesting that preventing V. vulnificus infection is essential.

Comparison of Surgical Outcomes and Predictors in Patients with Monomicrobial Necrotizing Fasciitis and Sepsis Caused by Vibrio vulnificus, Aeromonas hydrophila, and Aeromonas sobria

Background: Monomicrobial necrotizing fasciitis caused by Vibrio vulnificus, Aeromonas hydrophila, and Aeromonas sobria are often associated with high mortality rates. The purpose of this study was to compare the independent predictors related to outcomes between Vibrio vulnificus and Aeromonas species necrotizing fasciitis. Patients and Methods: Monomicrobial necrotizing fasciitis caused by Vibrio vulnificus (60 patients) and Aeromonas species (31 patients) over an 11-year period were reviewed retrospectively. Differences in mortality, patient characteristics, clinical presentations, and laboratory data were compared between the Vibrio vulnificus and Aeromonas species groups, and between the death and the survival subgroups of patients with Aeromonas species. Results: Six patients in the Vibrio vulnificus group (10%) and 11 in the Aeromonas species group (32.3%) died. Fifty-nine patents had bacteremia and 16 patients died (27.1%). Patients who had Vibrio vulnificus had a higher incidence of bacteremia. The patients who had Aeromonas species presenting with bacteremia were significantly associated with death. The death subgroup of patients with Aeromonas necrotizing fasciitis had a higher incidence of bacteremia, higher counts of banded leukocytes, lower platelet counts, lower total lymphocyte counts, and lower serum albumin level than the survival subgroup. Conclusions: Monomicrobial necrotizing fasciitis caused by Aeromonas species was characterized by more fulminating and higher mortality than that of Vibrio vulnificus, even after early fasciotomy and third-generation cephalosporin antibiotic therapy. Those risk factors, such as bacteremia, shock, lower platelet counts, lower albumin levels, and antibiotic resistance were associated with mortality, which should alert clinicians to pay more attention to and aggressively treat those patients with Aeromonas and Vibrio necrotizing fasciitis.

The Secretion of Toxins and Other Exoproteins of Cronobacter: Role in Virulence, Adaption, and Persistence

: Cronobacter species are considered an opportunistic group of foodborne pathogenic bacteria capable of causing both intestinal and systemic human disease. This review describes common virulence themes shared among the seven Cronobacter species and describes multiple exoproteins secreted by Cronobacter, many of which are bacterial toxins that may play a role in human disease. The review will particularly concentrate on the virulence factors secreted by C. sakazakii, C. malonaticus, and C. turicensis, which are the primary human pathogens of interest. It has been discovered that various species-specific virulence factors adversely affect a wide range of eukaryotic cell processes including protein synthesis, cell division, and ion secretion. Many of these factors are toxins which have been shown to also modulate the host immune response. These factors are encoded on a variety of mobile genetic elements such as plasmids and transposons; this genomic plasticity implies ongoing re-assortment of virulence factor genes which has complicated our efforts to categorize Cronobacter into sharply defined genomic pathotypes.

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.

Bioprospecting in the genomic age

The genomic revolution promises great advances in the search for useful biocatalysts. Function-based metagenomic approaches have identified several enzymes with properties that make them useful candidates for a variety of bioprocesses. As DNA sequencing costs continue to decline, the volume of genomic data, along with their corresponding predicted protein sequences, will continue to increase dramatically, necessitating new approaches to leverage this information for gene-based bioprospecting efforts. Additionally, as new functions are discovered and correlated with this sequence information, the knowledge of the often complex relationship between a protein's sequence and function will improve. This in turn will lead to better gene-based bioprospecting approaches and facilitate the tailoring of desired properties through protein engineering projects. In this chapter, we discuss a number of recent advances in bioprospecting within the context of the genomic age.

Vibrio zinc-metalloprotease causes photoinactivation of coral endosymbionts and coral tissue lesions

BACKGROUND

Coral diseases are emerging as a serious threat to coral reefs worldwide. Of nine coral infectious diseases, whose pathogens have been characterized, six are caused by agents from the family Vibrionacae, raising questions as to their origin and role in coral disease aetiology.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report on a Vibrio zinc-metalloprotease causing rapid photoinactivation of susceptible Symbiodinium endosymbionts followed by lesions in coral tissue. Symbiodinium photosystem II inactivation was diagnosed by an imaging pulse amplitude modulation fluorometer in two bioassays, performed by exposing Symbiodinium cells and coral juveniles to non-inhibited and EDTA-inhibited supernatants derived from coral white syndrome pathogens.

CONCLUSION/SIGNIFICANCE

These findings demonstrate a common virulence factor from four phylogenetically related coral pathogens, suggesting that zinc-metalloproteases may play an important role in Vibrio pathogenicity in scleractinian corals.

Isolation and characterization of metalloproteases with a novel domain structure by construction and screening of metagenomic libraries

Small-insert metagenomic libraries from four samples were constructed by a topoisomerase-based and a T4 DNA ligase-based approach. Direct comparison of both approaches revealed that application of the topoisomerase-based method resulted in a higher number of insert-containing clones per microg of environmental DNA used for cloning and a larger average insert size. Subsequently, the constructed libraries were partially screened for the presence of genes conferring proteolytic activity. The function-driven screen was based on the ability of the library-containing Escherichia coli clones to form halos on skim milk-containing agar plates. The screening of 80,000 E. coli clones yielded four positive clones. Two of the plasmids (pTW2 and pTW3) recovered from positive clones conferred strong proteolytic activity and were studied further. Analysis of the entire insert sequences of pTW2 (28,113 bp) and pTW3 (19,956 bp) suggested that the DNA fragments were derived from members of the genus Xanthomonas. Each of the plasmids harbored one gene (2,589 bp) encoding a metalloprotease (mprA, pTW2; mprB, pTW3). Sequence and biochemical analyses revealed that MprA and MprB are similar extracellular proteases belonging to the M4 family of metallopeptidases (thermolysin-like family). Both enzymes possessed a unique modular structure and consisted of four regions: the signal sequence, the N-terminal proregion, the protease region, and the C-terminal extension. The architecture of the latter region, which was characterized by the presence of two prepeptidase C-terminal domains and one proprotein convertase P domain, is novel for bacterial metalloproteases. Studies with derivatives of MprA and MprB revealed that the C-terminal extension is not essential for protease activity. The optimum pH and temperature of both proteases were 8.0 and 65 degrees C, respectively, when casein was used as substrate.

Two forms of Vibrio vulnificus metalloprotease VvpE are secreted via the type II general secretion system

Vibrio vulnificus has been known to secrete one form of metalloprotease VvpE (45 kDa) that is cleaved to 34 kDa-VvpE and 11 kDa-C-terminal propeptide via extracellular autoproteolysis. However, we found that extracellular secretion of both the 34 and 45 kDa forms of VvpE began in the early growth phase; moreover, 34 kDa-VvpE existed as the major form in V. vulnificus cell lysates and culture supernatants. In addition, extracellular secretion of both 34 and 45 kDa-VvpE was blocked by mutation of the pilD gene, which encodes for the type IV leader peptidase/N-methyltransferase of the type II general secretion system, and the blocked VvpE secretion was recovered by in trans-complementation of the wild-type pilD gene. These results indicate that 34 kDa-VvpE is the major form secreted along with 45 kDa-VvpE from the early growth phase via the PilD-mediated type II general secretion system.

Molecular cloning and sequence analysis of a novel zinc-metalloprotease gene from the Salinivibrio sp. strain AF-2004 and its extracellular expression in E. coli

In this work the first protease gene encoding a novel zinc-metalloprotease from the moderately halophilic bacterium Salinivibrio sp. strain AF-2004 has been cloned, sequenced and reported to the GenBank. We have generated a library containing about 10,000 transformants whose screening yielded one clone harboring plasmid pBluescript with 3.6 kb inserted fragment (pBlueSVP2) with positive caseinolytic activity. Nucleotide sequence analysis of the selected clone revealed a single open reading frame (ORF) of 1833 bp encoding 611 amino acids. The deduced amino acid sequence includes a zinc-metalloprotease HEXXH-E consensus motif which is highly conserved in the M4 family of proteases. The primary amino acid sequence alignment search in the database revealed a moderate homology between the deduced amino acid sequence and the known zinc-metalloproteases including vibriolysin from Vibrio vulnificus and Pseudomonas aeruginosa elastase. The full length of SVP2 gene was subcloned into pQE-80L (pQEVP1) and transformed into Escherichia coli BL21 (DE3) for recombinant overexpression of the protease. Following induction by IPTG, active enzyme was found within cells and in the extracellular medium, where it slowly accumulated to high levels. Mass spectrometric fingerprinting of trypsin digested rSVP2 analysis identified the processed mature protease which starts at Ala-200 of a SVP2 full length protein. Although this result suggested a mature protein of 412 amino acids (44.8 kDa), electrospray-ionisation mass spectrometry revealed that the molecular mass of purified rSVP2 was only 34.2 kDa, which indicates a further cleavage site at the C-terminal.

Phospholipid directed motility of surface-motile bacteria

Myxococcus xanthus is a surface-motile bacterium that has adapted at least one chemosensory system to allow directed movement towards the slowly diffusible lipid phosphatidylethanolamine (PE). The Dif chemosensory pathway is remarkable because it has at least three inputs coupled to outputs that control extracellular matrix (ECM) production and lipid chemotaxis. The methyl-accepting chemotaxis protein, DifA, has two different sensor inputs that have been localized by mutagenesis. The Dif chemosensory pathway employs a novel protein that slows adaptation. Lipid chemotaxis may play important roles in the M. xanthus life cycle where prey-specific and development-specific attractants have been identified. Lipid chemotaxis may also be an important mechanism for locating nutrients by lung pathogens such as Pseudomonas aeruginosa.

The C-terminal region of Bacteroides fragilis toxin is essential to its biological activity

To evaluate the role of the C-terminal region in Bacteroides fragilis toxin (BFT) activity, processing, and secretion, sequential C-terminal truncation and point mutations were created by site-directed mutagenesis. Determination of BFT activity on HT29/C1 cells, cleavage of E-cadherin, and the capacity to induce interleukin-8 secretion by wild-type BFT and C-terminal deletion mutants showed that deletion of only 2 amino acid residues at the C terminus significantly reduced BFT biological activity and deletion of eight or more amino acid residues obliterated BFT biologic activity. Western blot and reverse transcription-PCR analyses indicated that BFT mutants lacking seven or fewer amino acid residues in the C-terminal region are processed and expressed similar to wild-type BFT. However, BFT mutants lacking eight or more amino acids at the C terminus are expressed similar to wild-type BFT but are unstable. We concluded that the C terminus of BFT is not tolerant of modest amino acid deletions, suggesting that it is biologically important for BFT activity.

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.

Expression and processing of Vibrio anguillarum zinc-metalloprotease in Escherichia coli

The extracellular zinc-metalloprotease of Vibrio anguillarum is a secreted virulence factor. It is synthesized from the empA gene as a 611-residue preproprotease and processed to the active mature protease (EmpA) with concomitant secretion via the type II secretion pathway. Active EmpA has been found only in the V. anguillarum culture supernatant and the process of the activation seems to vary depending on strains analyzed. To better understand the mechanism of EmpA export and processing, the empA gene was cloned and expressed in Escherichia coli strains. Expression of empA did not have toxic effect on bacterial growth. Rupturing E. coli TOP10 cells by heating in gel-loading buffer resulted in activation of EmpA and severe proteolysis of the samples. In contrast, the same treatment of the E. coli MC4100A strain did not lead to the general proteolysis. In this strain, EmpA was exported into the periplasm via the Sec pathway. The periplasmic EmpA was detected in two active conformations. Therefore, in E. coli processing of EmpA precursor to an active enzyme did not require secretion to the media and the help of other V. anguillarum protein. Like in V. anguillarum, heterologous expression of empA in E. coli showed strain-specific activation process.

Vibrio vulnificus secretes a broad-specificity metalloprotease capable of interfering with blood homeostasis through prothrombin activation and fibrinolysis

Vibrio vulnificus is a causative agent of serious food-borne diseases in humans related to the consumption of raw seafood. It secretes a metalloprotease that is associated with skin lesions and serious hemorrhagic complications. In this study, we purified and characterized an extracellular metalloprotease (designated as vEP) having prothrombin activation and fibrinolytic activities from V. vulnificus ATCC 29307. vEP could cleave various blood clotting-associated proteins such as prothrombin, plasminogen, fibrinogen, and factor Xa, and the cleavage could be stimulated by addition of 1 mM Mn2+ in the reaction. The cleavage of prothrombin produced active thrombin capable of converting fibrinogen to fibrin. The formation of active thrombin appeared to be transient, with further cleavage resulting in a loss of activity. The cleavage of plasminogen, however, did not produce an active plasmin. vEP could cleave all three major chains of fibrinogen without forming a clot. It could cleave fibrin polymer formed by thrombin as well as the cross-linked fibrin formed by factor XIIIa. In addition, vEP could also cleave plasma proteins such as bovine serum albumin and gamma globulin, and its broad specificity is reflected in the cleavage sites, which include Asp207-Phe208 and Thr272-Ala273 bonds in prothrombin and a Tyr80-Leu81 bond in plasminogen. Taken together, the data suggest that vEP is a broad-specificity protease that could function as a prothrombin activator and a fibrinolytic enzyme to interfere with blood homeostasis as part of the mechanism associated with the pathogenicity of V. vulnificus in humans and thereby facilitate the development of systemic infection.

The FAXWXXT motif in the carboxyl terminus ofVibrio mimicusmetalloprotease is involved in binding to collagen

We have shown previously that the C-terminal region of the extracellular metalloprotease of Vibrio mimicus (VMC) is essential for collagenase activity. Here, we demonstrate that deletion of 100 amino acids, but not 67 amino acids, from the C-terminus of the intact VMC protein (VMC61) abolished the collagenase activity. The intervening 33-amino acid region contains a repeated FAXWXXT motif that is essential for insoluble type I collagen binding; the isolated 33-amino acid peptide bound to insoluble type I collagen, while a peptide containing only the first FAXWXXT motif did not. Compared to the VMC61, the 33-amino acid peptide corresponding to the C-terminus exhibited a similar binding affinity and a lower binding capacity.

Bacterial alpha2-macroglobulins: colonization factors acquired by horizontal gene transfer from the metazoan genome?

Homologs of metazoan α₂-macroglobulins have been found in bacteria. The distribution of these genes in diverse bacterial clades suggests they have been acquired by multiple horizontal transfers.

Background

Invasive bacteria are known to have captured and adapted eukaryotic host genes. They also readily acquire colonizing genes from other bacteria by horizontal gene transfer. Closely related species such as Helicobacter pylori and Helicobacter hepaticus, which exploit different host tissues, share almost none of their colonization genes. The protease inhibitor α₂-macroglobulin provides a major metazoan defense against invasive bacteria, trapping attacking proteases required by parasites for successful invasion.

Results

Database searches with metazoan α₂-macroglobulin sequences revealed homologous sequences in bacterial proteomes. The bacterial α₂-macroglobulin phylogenetic distribution is patchy and violates the vertical descent model. Bacterial α₂-macroglobulin genes are found in diverse clades, including purple bacteria (proteobacteria), fusobacteria, spirochetes, bacteroidetes, deinococcids, cyanobacteria, planctomycetes and thermotogae. Most bacterial species with bacterial α₂-macroglobulin genes exploit higher eukaryotes (multicellular plants and animals) as hosts. Both pathogenically invasive and saprophytically colonizing species possess bacterial α₂-macroglobulins, indicating that bacterial α₂-macroglobulin is a colonization rather than a virulence factor.

Conclusions

Metazoan α₂-macroglobulins inhibit proteases of pathogens. The bacterial homologs may function in reverse to block host antimicrobial defenses. α₂-macroglobulin was probably acquired one or more times from metazoan hosts and has then spread widely through other colonizing bacterial species by more than 10 independent horizontal gene transfers. yfhM-like bacterial α₂-macroglobulin genes are often found tightly linked with pbpC, encoding an atypical peptidoglycan transglycosylase, PBP1C, that does not function in vegetative peptidoglycan synthesis. We suggest that YfhM and PBP1C are coupled together as a periplasmic defense and repair system. Bacterial α₂-macroglobulins might provide useful targets for enhancing vaccine efficacy in combating infections.

Characterization of the enzyme activity of an extracellular metalloprotease (VMC) from Vibrio mimicus and its C-terminal deletions

To investigate the enzymatic properties of Vibrio mimicus metalloprotease, the mature metalloprotease gene (vmc) was overexpressed in Escherichia coli and the recombinant protein (rVMC61) was purified by metal affinity chromatography. rVMC61 showed maximum activity at about 37 degrees C, pH 8. The purified rVMC61 was very specific toward collagen substrates, such as gelatin, type I, II, and III collagens and synthetic peptides (Cbz-GPLGP and Cbz-GPGGPA). But it did not show degrading activity toward other biological proteins including lysozyme, lactoferrin and bovine serum albumin. rVMC61 also showed cytotoxicity against CHSE-214 fish cells. To examine the role of the C-terminal region of rVMC61, the 3' end of the metalloprotease gene (vmc) was digested serially with exonuclease III. The truncated vmc derivatives encoding 57-42 kDa of the protease were isolated and overexpressed in E. coli. The collagenase activities of truncated proteins were investigated using gelatin as substrate. Deletion of 100 amino acids from the C-terminus resulted in loss of gelatin degrading activity. However, deletion of 67 amino acids from the C-terminus did not affect its gelatin degrading activity.

Histamine-releasing reaction induced by the N-terminal domain of Vibrio vulnificus metalloprotease

A zinc metalloprotease secreted by Vibrio vulnificus, an opportunistic human pathogen causing septicemia and wound infection, stimulates exocytotic histamine release from rat mast cells. This protease consists of two functional domains: the N-terminal domain that catalyzes proteolytic reaction and the C-terminal domain that promotes the association with a protein substrate or cell membrane. Like the intact protease, the N-terminal domain alone also induced histamine release from rat peritoneal mast cells in a dose- and time-dependent manner. However, the reaction induced was apparently weak and went on more slowly. The nickel-substituted protease or its N-terminal domain, each of which has the reduced proteolytic activity due to decreased affinity to a substrate, showed much less histamine-releasing activity. When injected into the rat dorsal skin, the N-terminal domain also evoked enhancement of the hypodermic vascular permeability, while the activity was comparable to that of the protease. Taken together, the protease may stimulate histamine release through the action of the catalytic center of the N-terminal domain on the target substance(s) on the mast cell membrane. The C-terminal domain may support the in vitro action of the N-terminal domain by coordination of the association of the protease with the membrane, but it may not modulate the in vivo action.