Pathogenic potentials of bacterial proteases

Matrix metalloproteinases: The sculptors of chronic cutaneous wounds

Cutaneous wound healing is a complex mechanism with multiple processes orchestrating harmoniously for structural and functional restoration of the damaged tissue. Chronic non-healing wounds plagued with infection create a major healthcare burden and is one of the most frustrating clinical problems. Chronic wounds are manifested by prolonged inflammation, defective re-epithelialization and haphazard remodeling. Matrix metalloproteinases (MMPs) are zinc dependent enzymes that play cardinal functions in wound healing. Understanding the pathological events mediated by MMPs during wound healing may pave way in identifying novel drug targets for chronic wounds. Here, we discuss the functions and skewed regulation of different MMPs during infection and chronic tissue repair. This review also points out the potential of MMPs and their inhibitors as therapeutic agents in treating chronic wounds during distinct phases of the wound healing. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

Design, synthesis, evaluation and thermodynamics of 1-substituted pyridylimidazo[1,5-a]pyridine derivatives as cysteine protease inhibitors

Targeting papain family cysteine proteases is one of the novel strategies in the development of chemotherapy for a number of diseases. Novel cysteine protease inhibitors derived from 1-pyridylimidazo[1,5-a]pyridine representing pharmacologically important class of compounds are being reported here for the first time. The derivatives were initially designed and screened in silico by molecular docking studies against papain to explore the possible mode of action. The molecular interaction between the compounds and cysteine protease (papain) was found to be very similar to the interactions observed with the respective epoxide inhibitor (E-64c) of papain. Subsequently, compounds were synthesized to validate their efficacy in wet lab experiments. When characterized kinetically, these compounds show their K_i and IC₅₀ values in the range of 13.75 to 99.30 µM and 13.40 to 96.50 µM, respectively. The thermodynamics studies suggest their binding with papain hydrophobically and entropically driven. These inhibitors also inhibit the growth of clinically important different types of Gram positive and Gram negative bacteria having MIC₅₀ values in the range of 0.6–1.4 µg/ml. Based on Lipinski’s rule of Five, we also propose these compounds as potent antibacterial prodrugs. The most active antibacterial compound was found to be 1-(2-pyridyl)-3-(2-hydroxyphenyl)imidazo[1,5-a]pyridine (3a).

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.

A robust plate assay for detection of extracellular microbial protease activity in metagenomic screens and pure cultures

A robust, efficient and cost-effective agar that utilises lactose free milk powder for identification of bacterial protease activity in pure cultures and metagenomic screens has been developed and tested on protease positive bacteria, selected strains and false protease positives isolated from a previously constructed metagenomic library.

Serratia marcescens serralysin induces inflammatory responses through protease-activated receptor 2

The Serratia marcescens-derived protease serralysin is considered to play an important role in the pathogenesis of infection. Protease-activated receptor 2 (PAR-2) is activated by trypsin and also several other trypsin-like serine proteases, leading to the modulation of inflammatory and immune responses. However, little is known about the activation of PAR-2 by bacterial proteases and its roles in bacterial infection. In this study, we investigated whether S. marcescens serralysin activates host inflammatory responses through PAR-2. Our results demonstrated that serralysin induces interleukin-6 (IL-6) and IL-8 mRNA expression in a human lung squamous cell carcinoma, EBC-l cells. In addition, serralysin activated activator protein 1 (AP-1)-, CCAAT/enhancer-binding protein (C/EBP)-, and nuclear factor-kappaB (NF-kappaB)-driven promoters in EBC-1 cells. An electrophoretic mobility shift assay showed that serralysin activates the binding of AP-1, C/EBPbeta, and NF-kappaB in the cells. Inactivation of serralysin resulted in the failure of transactivation of AP-1-, C/EBP-, and NF-kappaB-driven promoters in the cells. Furthermore, serralysin activated AP-1-, C/EBP-, and NF-kappaB-driven promoters via PAR-2 in HeLa cells. PAR-2 antagonist peptides decreased serralysin-induced transactivation of AP-1-, C/EBP-, and NF-kappaB-driven promoters in EBC-1 cells. Considered together, these results suggest that serralysin requires PAR-2 to activate the critical transcription factors AP-1, C/EBPbeta, and NF-kappaB for host inflammatory responses.

Molecular and functional characterization of a ToxR-regulated lipoprotein from a clinical isolate of Aeromonas hydrophila

Human diseases caused by species of Aeromonas have been classified into two major groups: septicemia and gastroenteritis. In this study, we reported the molecular and functional characterization of a new virulence factor, ToxR-regulated lipoprotein, or TagA, from a diarrheal isolate, SSU, of Aeromonas hydrophila. The tagA gene of A. hydrophila exhibited 60% identity with that of a recently identified stcE gene from Escherichia coli O157:H7, which encoded a protein (StcE) that provided serum resistance to the bacterium and prevented erythrocyte lysis by controlling classical pathway of complement activation by cleaving the complement C1-esterase inhibitor (C1-INH). We purified A. hydrophila TagA as a histidine-tagged fusion protein (rTagA) from E. coli DE3 strain using a T7 promoter-based pET30 expression vector and nickel affinity column chromatography. rTagA cleaved C1-INH in a time-dependent manner. The tagA isogenic mutant of A. hydrophila, unlike its corresponding wild-type (WT) or the complemented strain, was unable to cleave C1-INH, which is required to potentiate the C1-INH-mediated lysis of host and bacterial cells. We indeed demonstrated colocalization of C1-INH and TagA on the bacterial surface by confocal fluorescence microscopy, which ultimately resulted in increased serum resistance of the WT bacterium. Likewise, we delineated the role of TagA in contributing to the enhanced ability of C1-INH to inhibit the classical complement-mediated lysis of erythrocytes. Importantly, we provided evidence that the tagA mutant was significantly less virulent in a mouse model of infection (60%) than the WT bacterium at two 50% lethal doses, which resulted in 100% mortality within 48 h. Taken together, our data provided new information on the role of TagA as a virulence factor in bacterial pathogenesis. This is the first report of TagA characterization from any species of Aeromonas.

A survey for phosphoglucose isomerase with lysyl aminopeptidase activity in Vibrionaceae and non-Vibrio pathogens

Phosphoglucose isomerase (PGI) with a novel lysyl aminopeptidase (LysAP) activity was recently purified and characterized from Vibrio vulnificus. We showed that it cleaves the amino-terminal lysyl residue from des-Arg(10)-kallidin to produce des-Arg(9)-bradykinin, suggesting that it plays a role in virulence. A survey was conducted to determine the presence of this potential virulence-enhancing enzyme among twenty-three halotolerant human and fish pathogens from eleven species within the Vibrionaceae family, including V. vulnificus, V. parahaemolyticus, V. cholerae, Aeromonas hydrophila, and Plesiomonas shigelloides. In addition, fourteen species of non-Vibrionaceae pathogens were screened for LysAP activity. Cell lysates were partially purified by anion exchange chromatography and fractions were screened for LysAP and isomerase activities. PGI-LysAP activity was detected in chromatographic fractions from all the Vibrio species tested, but was not detected in any of the non-Vibrionaceae pathogens. Levels of isomerase and LysAP activity correlated (R(2)=0.92) for nine strains of V. vulnificus. Since the Vibrionaceae represent an important family of human and fish pathogens, our identification of PGI-LysAP activity in a broad array of vibrios may lead to the development of improved analytical methods for their identification as well as interventions to reduce the high morbidity and mortality associated with some Vibrionaceae infections in clinical, veterinary, and aquaculture settings.

Antiprotease inactivation by Salmonella enterica released from infected macrophages

The mammalian serine protease plasmin, which has an important role in extracellular matrix degradation during cell migration, is regulated by the plasma antiprotease alpha(2)-antiplasmin (alpha(2)AP). The surface protease PgtE of Salmonella enterica serovar Typhimurium proteolytically inactivated alpha(2)AP. PgtE also activates the plasma zymogen plasminogen to plasmin, and bacteria expressing PgtE promoted degradation of extracellular matrix laminin in the presence of plasminogen and alpha(2)AP. alpha(2)AP inactivation was detected with the rough derivative of S. enterica 14028, but not with the smooth wild-type strain, suggesting that the O-antigen of lipopolysaccharide prevented contact of PgtE with the substrate molecule. After growth of S. enterica 14028 in murine J774A.1 macrophage-like cells, the infected cell lysate as well as bacteria from isolated Salmonella-containing vacuoles (SCVs) cleaved alpha(2)AP. Bacteria from SCVs produced an elevated level of PgtE and had a reduced O-antigen chain length. The lysate from S. enterica 14028-infected macrophages promoted formation of plasmin in the presence of alpha(2)AP, whereas plasmin formation by lysates from uninfected macrophages, or from macrophages infected with the pgtE-negative derivative of 14028, was inhibited by alpha(2)AP. Salmonella disseminates in the host within macrophages, which utilize plasmin for migration through tissue barriers. The results suggest that intracellular enhancement of PgtE activity in Salmonella may promote macrophage-associated proteolysis and cellular migration by altering the balance between host plasmin and alpha(2)AP.

Characterization of a lysyl aminopeptidase activity associated with phosphoglucose isomerase of Vibrio vulnificus

Phosphoglucose isomerase (PGI) is a multifunctional enzyme involved in glycolysis and gluconeogenesis and, in mammalian cells, functions as neuroleukin, autocrine motility factor (AMF), and differentiation and maturation factor (MF). We isolated and characterized PGI with a novel lysyl aminopeptidase (LysAP) activity (PGI-LysAP) from Vibrio vulnificus. Mass spectrometry revealed that PGI-LysAP is a heterodimer consisting of 23.4- and 60.8-kDa subunits. Only the heterodimer displayed LysAP activity. PGI-LysAP has a pI around 6.0 and high specificity toward the synthetic, fluorogenic substrate l-lysyl-7-amino-4-methylcoumarin. LysAP activity is optimal at pH 8.0, is 64% higher at 37 degrees C than at 21 degrees C, does not directly correlate with virulence, and is strongly inhibited by serine protease and metalloprotease inhibitors. PGI-LysAP was also identified in Vibrio parahaemolyticus and V. cholerae, but was absent from non-Vibrio human pathogens. Sequencing of the pgi gene revealed 1653 bp coding for a 550-amino-acid protein. Cloned and expressed PGI formed a homodimer with isomerase activity, but not LysAP activity. The finding of LysAP activity associated with heterodimeric PGI should foster a broad search for putative substrates in an effort to elucidate the role of PGI-LysAP in bacteria and its roles in the pathophysiology of diseases.

Characterization of a cytotoxic factor in culture filtrates of Serratia marcescens

Serratia marcescens culture filtrates have been reported to be cytotoxic to mammalian cells. Using biochemical and genetic approaches, we have identified a major source of this cytotoxic activity. Both heat and protease treatments abrogated the cytotoxicity of S. marcescens culture filtrates towards HeLa cells, suggesting the involvement of one or more protein factors. A screen for in vitro cytotoxic activity revealed that S. marcescens mutant strains that are deficient in production of a 56-kDa metalloprotease are significantly less cytotoxic to mammalian cells. Cytotoxicity was significantly reduced when culture filtrates prepared from wild-type strains were pretreated with either EDTA or 1,10-phenanthroline, which are potent inhibitors of the 56-kDa metalloprotease. Furthermore, cytotoxic activity was restored when the same culture filtrates were incubated with zinc divalent cations, which are essential for enzymatic activity of the 56-kDa metalloprotease. Finally, recombinant expression of the S. marcescens 56-kDa metalloprotease conferred a cytotoxic phenotype on the culture filtrates of a nonpathogenic Escherichia coli strain. Collectively, these data suggest that the 56-kDa metalloprotease contributes significantly to the in vitro cytotoxic activity commonly observed in S. marcescens culture filtrates.

SMANCS and polymer-conjugated macromolecular drugs: advantages in cancer chemotherapy

This review discusses the development and therapeutic potential of prototype macromolecular drugs for use in cancer chemotherapy, in particular the development and use of SMANCS, a conjugate of neocarzinostatin and poly(styrene-comaleic acid). The various topics covered include a brief description of the chemistry and polymer conjugation, the binding of the conjugate to albumin and the biological behaviour in vitro and in vivo after arterial injection in animals, including plasma half-life, and the lipid solubility of SMANCS in medium chain triglycerides and Lipiodol, a lipid contrast medium suitable for use in X-ray-computed tomography. The biological response-modifying effects and the tumor-targeting mechanism of SMANCS and other macromolecular drugs are also discussed. The latter mechanism is accounted for in terms of a tumor 'enhanced permeability and retention' (or EPR) effect. A principal advantage in the use of SMANCS or other macromolecular drugs is the potential for a reduction or elimination of toxicity. Macromolecular drugs such as a pyran copolymer-NCS conjugate show a marked reduction in bone marrow toxicity normally associated with the use of NCS. This is believed to be due to a hypothetical blood-bone marrow 'barrier' which, relative to NCS, restricts or limits access of the macromolecular drug to the bone marrow. In addition, the clinical possibilities for SMANCS are discussed, including the suggestion that angiotensin II-induced hypertension has clinical potential in improving the selective delivery of macromolecular drugs (i.e. SMANCS) to tumors. Aqueous SMANCS formulations have been tested in pilot studies in patients with solid tumors of the ovary, esophagus, lung, stomach, adrenal gland and in the brain. Formulations based on SMANCS/Lipiodol have been shown to be effective both as a diagnostic tool and for therapeutic use in solid tumors where the formulations are given arterially via a catheter. In a pilot study in primary unresectable hepatoma, an objective reduction in tumor size was observed for about 90% of cases when an adequate amount of the macromolecular drug was administered. A patient receiving such treatment with no active liver cirrhosis and tumor nodules/lesion confined within one liver segment might expect to have a 90% chance of survival after treatment for at least 5 years.

Serratia marcescens keratitis: strain-specific corneal pathogenesis in rabbits

PURPOSE

The purpose of this study was to develop an animal model of Serratia keratitis that is suitable to demonstrate the pathology of specific strains.

METHODS

Serratia marcescens ocular strains 93-1399-1 and 94-EI-185-2, and an environmental strain (ATCC 14041) were characterized in vitro in terms of their motility, metabolic profiles, ribotypes, and protease production. The strains were then analyzed in the rabbit intrastromal injection model. Slit lamp examination (SLE) and enumeration of bacteria in the cornea was conducted every 6 hours for 30 hours post-infection. In vivo motilities were analyzed by quantification of bacteria in the peripheral and central areas of infected rabbit corneas.

RESULTS

All strains were similar in their metabolic activity and production of extracellular proteases. The ocular isolates were distinct from the environmental strain in their ribotyping patterns and in their motility. Each strain grew logarithmically in the cornea up to 6 hours post-infection. SLE scores increased from 0 to 30 hours post-infection for strains ATCC 14041 and 93-1399-1, while the SLE score of strain 94-EI-185-2 reached its maximum at 18 hours post-infection. Strain-specific differences in pathology were noted from 18 to 30 hours post-infection. Strain 94-EI-185-2 produced iritis but only mild corneal changes. Strain 93-1399-1 produced a severe corneal infiltrate encompassing the entire corneal surface as well as severe conjunctival inflammation and iritis. Strain ATCC 14041 produced a localized, severe, exudative corneal abscess that contained infecting bacteria.

CONCLUSIONS

A rabbit model of Serratia keratitis was developed in which bacterial growth kinetics and strain-specific ocular pathologic changes were reproducible.

Involvement of bradykinin generation in intravascular dissemination of Vibrio vulnificus and prevention of invasion by a bradykinin antagonist

Involvement of bradykinin generation in bacterial invasion was examined by using a gram-negative bacillus, Vibrio vulnificus, which is known to invade the blood circulatory system and cause septicemia. V. vulnificus was injected intraperitoneally (i.p.) into mice with or without bradykinin or a bradykinin (B2 receptor) antagonist. Dissemination of V. vulnificus from peritoneal septic foci to the circulating blood was assessed by counting of viable bacteria in venous blood by use of the colony-forming assay. Intravascular dissemination of V. vulnificus in mice was significantly potentiated by simultaneous injection with bradykinin but was markedly reduced by coadministration with the B2 antagonist D-Arg,[Hyp3, Thi(5,8), D-Phe7]-bradykinin. Furthermore, V. vulnificus lethality was significantly increased when bradykinin was administered simultaneously with the bacillus, whereas it was definitely suppressed by treatment with D-Arg,[Hyp3, Thi(5,8), D-Phe7]-bradykinin. Similarly, ovomacroglobulin, a potent inhibitor of the V. vulnificus protease, showed a strong suppressive effect on the V. vulnificus septicemia. We also confirmed appreciable bradykinin production in the primary septic foci in the mouse peritoneal cavity after i.p. inoculation with V. vulnificus. It is thus concluded that bradykinin generation in infectious foci is critically involved in facilitation of intravascular dissemination of V. vulnificus.

Activation of human matrix metalloproteinases by various bacterial proteinases

Matrix metalloproteinases (MMPs) are zinc-containing proteinases that participate in tissue remodeling under physiological and pathological conditions. To test the involvement of bacterial proteinases in tissue injury during bacterial infections, we investigated the activation potential of various bacterial proteinases against precursors of MMPs (proMMPs) purified from human neutrophils (proMMP-8 and -9) and from human fibrosarcoma cells (proMMP-1). Each proMMP was subjected to treatment with a series of bacterial proteinases at molar ratios of 0.01-0.1 (bacterial proteinase to proMMP), and activities of MMPs generated were determined. Among six different bacterial proteinases, thermolysin family enzymes (family M4) such as Pseudomonas aeruginosa elastase, Vibrio cholerae proteinase, and thermolysin strongly activated all three proMMPs via limited proteolysis to generate active forms of the MMPs. N-terminal sequence analysis of the active MMPs revealed that cleavage occurred at the Val82-Leu83 and Thr90-Phe91 bonds of proMMP-1 and proMMP-9, respectively, which are located near the N terminus of the catalytic domain of MMPs. In contrast, Serratia 56-kDa proteinase and Pseudomonas alkaline proteinase, both of which are classified as members of the serralysin subfamily of zinc metalloproteinases (family M10), and Serratia 73-kDa thiol proteinase did not evidence proteolytic processing or activation of proMMP-1, -8, and -9 under these experimental conditions. These results indicate that bacterial proteinases may play an important role in tissue destruction and disintegration of extracellular matrix at the site of infections.

Bradykinin generation triggered by Pseudomonas proteases facilitates invasion of the systemic circulation by Pseudomonas aeruginosa

To elucidate the mechanism of bacterial exoprotease in promotion of the intravascular dissemination of Pseudomonas aeruginosa, we examined the possible involvement of bradykinin (whose generation is induced by pseudomonal proteases in septic foci) in the invasion by bacteria, and in access of bacterial toxins to systemic blood circulation. P. aeruginosa 621 (PA 621), which produces very little protease, was injected intraperitoneally into mice together with pseudomonal exoproteases (elastase/alkaline protease). Dissemination of bacteria from the peritoneal septic foci to the blood was assessed by counting viable bacteria in the blood and spleen by use of the colony-forming assay. The results showed that pseudomonal proteases markedly enhanced (10- to 100-fold) intravascular dissemination of bacteria in mice. This enhancement was induced not only by pseudomonal proteases but also by bradykinin. More importantly, the increased spread of PA 621 induced by pseudomonal protease and bradykinin was significantly augmented by the addition of kininase inhibitors, indicating the direct involvement of bradykinin in bacterial dissemination. Similarly, bradykinin caused effective dissemination of pseudomonal toxins such as endotoxin (lipopolysaccharide) and exotoxin A when the toxins were injected into the peritoneal cavity with bradykinin. Furthermore, the lethality of the infection with PA 621 was strongly enhanced by pseudomonal proteases given i.p. simultaneously with PA 621. On the basis of these results, it is strongly suggested that pseudomonal proteases as well as bradykinin generated in infectious foci are involved in facilitation of bacterial dissemination in vivo.

Further evidence of bradykinin involvement in septic shock: reduction of kinin production in vivo and improved survival in rats by use of polymer tailored SBTI with longer t1/2

Involvement of bradykinin in septic shock and its therapeutic endeavor using soybean trypsin inhibitor (SBTI, Kunitz type) were investigated in an in vivo model of septic shock induced by pseudomonal elastase. Pseudomonal elastase injection at 0.5 mg/kg i.v. to guinea pigs resulted in elevation level of bradykinin in the blood from < 1 ng/ml to 25 ng/ml which was accompanied by a drop of mean arterial blood pressure (MABP) (about 45 mmHg). When native soybean trypsin inhibitor (SBTI, Kunitz type, 20 kDa) was injected, into this model, induction of bradykinin generation and hypotension by the bacterial protease treatment was completely obliterated as judged by the both levels of bradykinin and MABP. Specifically, by the treatment with SBTI, bradykinin levels did not increase and the drop of the blood pressure was minimal (< 10 mmHg) in this time frame (< 30 min). We designed and prepared succinylated gelatin-conjugated SBTI (suc-gel SBTI) with enlarged molecular mass (M(r) approximately 110,000) and higher area under the curve of the plasma concentration, which exhibits about 6 times longer plasma half-life (t1/2) and about 4 times larger area under the curve of plasma concentration. Suc-gel-SBTI suppressed the pseudomonal protease-induced shock much more effectively than native SBTI, the conjugate exhibited its effect for more than 3 h, while the native SBTI showed the effect only within 2 h after i.v. injection.

Pathogenic mechanisms induced by microbial proteases in microbial infections

Most bacterial and fungal proteases excreted into infected hosts exhibit a wide range of pathogenic potentials ranging from pain, edema or even shock to translocation of bacteria from the site of infection into systemic circulation, thus resulting in septicemia. The basic mechanism or principle common to all these phenomena is explained by kinin generation, either directly from high- and/or low-molecular weight kininogens or indirectly via activation of the bradykinin generating cascade: i.e. Hageman factor-->activated Hageman factor-->prekallikrein-->kallikrein-->high-molecular weight kininogen-->bradykinin. Some bacterial proteases are also involved in activation of other host protease zymogens such as plasminogen, procollagenase (matrix metallo proteases) and proenzymes of the clotting system. Furthermore, most bacterial proteases are not only resistant to plasma protease inhibitors of the hosts, most of which belong to a group of serine protease inhibitors called serpins (serine protease inhibitors), but they also quickly inactivate serpins. Some bacterial proteases may also activate bacterial toxins thus rendering toxigenic pathogenesis. They are also capable of degrading immunoglobulins and components of the complement system and facilitate propagation of micro organisms. All in all, microbial proteases are very critical in enhancing pathogenesis of severe diseases. It is also noteworthy that bacterial cell wall components themselves, i.e. endotoxin (or lipopolysaccharide) of gram negative bacteria and teichoic/lipoteichoic acid of gram positive bacteria, are also able to activate the bradykinin generating cascade-involving activation of Hageman factor as mentioned above.

Association of colony variation in Serratia marcescens with the differential expression of protease and type 1 fimbriae

Several clinical isolates of Serratia marcescens were found to dissociate on peptone glycerol agar into colonies with red and pink or white and gray phenotypes that differ in the expression of proteolytic activity and mannose-sensitive type of hemagglutination. Colonies of red and white type were proteolytically active but did not express hemagglutination, whereas pink and gray colonies were protease-deficient but agglutinated guinea pig erythrocytes. Site-directed mutagenesis of a red laboratory strain S. marcescens SM6 resulted in selection of protease negative derivative prt::G7 which expressed the pink phenotype with hemagglutinating activity. It is suggested that a DNA-regulatory element may be involved in this type of colony variation.

Are bacterial proteinases pathogenic factors?

Evidence is rapidly accumulating that suggests that the growth and proliferation of pathogenic bacteria depend on proteolytic enzymes of the invading organism and of the host. Proteinase inhibitors targeting bacterial proteinases may be useful antimicrobial agents.

Characterization of a plasminogen activator produced by Acanthamoeba castellanii

Serine proteases play an important role in a diverse array of biological processes, including embryogenesis, metastasis, angiogenesis, thrombolysis and tissue invasion by certain parasites. The latter observation prompted us to explore the possibility that the tissue-invasive ocular parasite Acanthamoeba castellanii elaborates one or more serine proteases. Acanthamoeba sp. are pathogenic free-living amoebae that can produce an invasive, blinding inflammatory disease of the cornea, termed Acanthamoeba keratitis. The present study reports the preliminary purification and characterization of a novel plasminogen activator from an ocular isolate of A. castellanii. The parasite-derived enzyme has a molecular mass of approx. 40 kDa and produces a single band of lysis on fibrinogen-agarose zymographs. Activity of the enzyme is completely inhibited by treatment with diisopropylfluorophosphate, indicating that it is a serine protease. The parasite-derived serine protease is not inhibited by amiloride which is a strong inhibitor of urokinase-type plasminogen activator. Additionally, the enzyme is not inhibited by plasminogen activator inhibitor-1 which is the primary physiological inhibitor of both urokinase and tissue-type plasminogen activator. It does not cross-react with antibodies specific for human urokinase or tissue-type plasminogen activator. The parasite-derived enzyme activates plasminogen from several mammalian species, including human, cow and pig. Thus, it is possible that this parasite-derived serine protease contributes to the pathogenesis of Acanthamoeba keratitis.

An IgE-binding TAME esterase in the urine of the mouse, Mus musculus domesticus

Among the highly heterogeneous components of the mouse urinary protein complex (MUP) a hydrolase was detected which was capable of spliting the proteinase ester substrate TAME as well as a synthetic chromogenic tripeptide specific for tissue and urinary kallikreins. The binding of mouse-specific IgE antibodies from the serum of a highly mouse-allergic patient occurred preferentially to this kallikrein-like enzyme. This finding underscores the possible association of significant biological activities with predominant IgE-binding allergens, especially in view of the strongly sensitizing potential and the known messenger functions of the MUP proteins.

Virulence of a Porphyromonas gingivalis W83 mutant defective in the prtH gene

In a previous study we cloned and determined the nucleotide sequence of the prtH gene from Porphyromonas gingivalis W83. This gene specifies a 97-kDa protease which is normally found in the membrane vesicles produced by P. gingivalis and which cleaves the C3 complement protein under defined conditions. We developed a novel ermF-ermAM antibiotic resistance gene cassette, which was used with the cloned prtH gene to prepare an insertionally inactivated allele of this gene. This genetic construct was introduced by electroporation into P. gingivalis W83 in order to create a protease-deficient mutant by recombinational allelic exchange. The mutant strain, designated V2296, was compared with the parent strain W83 for proteolytic activity and virulence. Extracellular protein preparations from V2296 showed decreased proteolytic activity compared with preparations from W83. Casein substrate zymography revealed that the 97-kDa proteolytic component as well as a 45-kDa protease was missing in the mutant. In in vivo experiments using a mouse model, V2296 was dramatically reduced in virulence compared with the wild-type W83 strain. A molecular survey of several clinical isolates of P. gingivalis using the prtH gene as a probe suggested that prtH gene sequences were conserved and that they may have been present in multiple copies. Two of 10 isolates did not hybridize with the prtH gene probe. These strains, like the V2296 mutant, also displayed decreased virulence in the mouse model. Taken together, these results suggest an important role for P. gingivalis proteases in soft tissue infections and specifically indicate that the prtH gene product is a virulence factor.

Molecular and biochemical characterization of a protective 40-kilodalton antigen from Corynebacterium pseudotuberculosis

A 40-kDa protein from Corynebacterium pseudotuberculosis has been previously identified as a protective antigen against ovine caseous lymphadenitis. From genomic DNA libraries of C. pseudotuberculosis, we have cloned and sequenced the 40-kDa protein gene, which was found to contain an open reading frame of 1,137 bp encoding a protein of 379 amino acids. No significant homology with previously published DNA or amino acid sequence data was found in databases, suggesting that this is a novel protein. Recombinant 40-kDa protein was overexpressed as a fusion protein to 15% of total cell proteins in Escherichia coli. Biochemical analysis of native and recombinant 40-kDa proteins has revealed associated proteolytic activity, which was shown to be of the serine protease type through the use of specific inhibitors. We suggest that this novel protective antigen be termed corynebacterial protease 40 (CP40).

Phosphinic peptide analogues as potent inhibitors of Corynebacterium rathayii bacterial collagenase

Pseudo-substrate analogues of collagenase from Corynebacterium rathayii, in which the scissile peptide bond is replaced by a phosphinic moiety, were synthesized and evaluated as inhibitors of this enzyme. The phosphinic tetrapeptide, Z-Phe-psi(PO2CH2)-Gly-Pro-Nle (1), was found to be a potent inhibitor of collagenase with a Ki value of 8 nM. Increasing the length of the phosphinic-containing inhibitors from tetra- to hepta-peptide size further improves the potency of these compounds. The heptapeptide analogue, Z-Phe-Gly-Pro-Phe-psi(PO2CH2)-Gly-Pro-Nle-OMe, with a Ki value of 0.6 nM, is the most potent inhibitor reported to date for bacterial collagenases. A comparison between the phosphinic analogue Z-Phe-psi(PO2CH2)-Gly-Pro-Nle (1) and the phosphonamide peptide Z-Phe-psi(PO2NH)-Gly-Pro-Nle (2) shows that for bacterial collagenase the replacement of a CH2 by an NH group results only in a modest increase in affinity from Ki = 8 nM for compound 1 to Ki = 6 nM for compound 2. Most of the phosphorus-containing inhibitors of this series are slow- or slow-tight-binding inhibitors with second-order rate constants for association and dissociation varying respectively for the kon values from 1 x 10(3) to 26 x 10(3) M-1.s-1 and for the koff values from 3 x 10(-4) to 2 x 10(-5) s-1. Interestingly, the lower affinity of the molecule containing a D residue in the P1 position of the inhibitor, compared with the molecule with an L residue in this position, is mainly the consequence of a lower rate constant for association of these D stereoisomers with the enzyme. This study demonstrates that phosphinic peptide analogues are potent inhibitors of a bacterial collagenase. The development of new phosphinic peptides should lead to the discovery of potent inhibitors of other zinc metalloproteases. Details of how the analogues were synthesized are given in Supplementary Publication SUP 50176 (14 pages), which has been deposited with the British Library Document Supply Centre, Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, from whom copies can be obtained on the terms indicated in Biochem. J. (1994) 297, 9.

Zymographic techniques for detection and characterization of microbial proteases

We have presented a variety of zymographic techniques for identification and characterization of microbial proteases, using SDS-PAGE and PAGE in nondissociating gels. Techniques are described using copolymerized protein substrates, diffusable protein substrates, protein substrates incorporated into indicator gels, as well as synthetic esterase substrates. When a newly discovered protease is being characterized, it is advisable to try a variety of techniques, both to determine optimal conditions for enzyme detection and to characterize the protease. Zymography is a versatile two-stage technique involving protein separation by electrophoresis followed by detection of proteolytic activity. Each particular combination of protease separation and detection techniques had advantages and limitations. Protease separation by SDS-PAGE has as a limitation the fact that some proteases do not renature and hence cannot be detected following treatment with SDS. However, it has an advantage the fact that it allows estimation of the relative molecular weight of proteases. Protein separation using nondissociating PAGE is performed using much gentler protease inactivation conditions than those produced by treatment with SDS. Like SDS-PAGE, nondissociating PAGE permits detection of multiple forms of enzymes; however, a disadvantage is that it cannot be used to obtain molecular weight estimates of proteases. The main variable to control during development of zymograms is the length of time of incubations. Increasing incubation (development) time generally increases the sensitivity of protease detection; however, as the length of time of incubation increases so does the extent of diffusion of proteases and substrates. If incubations are prolonged, protease bands will diffuse, decreasing resolution. Additionally, zones of lysis produced by closely migrating proteolytically active species will merge, eliminating the possibility of detecting all proteolytic species in the sample. Zymographic techniques can be extremely useful in identification and characterization of microbial proteases. If a few properties of a protease are known, such as the pH range over which the enzyme is active, and whether it can renature after exposure to SDS, zymographic techniques can be specifically and readily adapted to optimize conditions for detection and assist in characterization of the enzyme.

Regulation of proteolytic activity in tissues

Degradation of tissue proteins is controlled by multiple means. These include regulation of the synthesis of proteinases, activation of the zymogen forms, the activity of the mature proteinase, and the degradation of these enzymes and the substrates. Mature proteinases can be controlled by pH, calcium ions, ATP, lipids and the formation of complexes with other proteinases, proteoglycans, and inhibitors.

Vascular permeability enhancing activity of Porphyromonas gingivalis protease in guinea pigs

Porphyromonas gingivalis protease, which had been isolated from a culture supernatant, caused vascular permeability enhancement in a dose-dependent manner when injected into guinea pig skin. The permeability-enhancing reaction caused by the protease was not affected by treatment with antihistamine, but was greatly augmented by simultaneous injection of a kinin potentiator, carboxypeptidase N inhibitor. However, the reaction was inhibited by soybean trypsin inhibitor or alpha 2-antiplasmin, although both of these inhibitors could not inhibit P. gingivalis protease at all by themselves. A bradykinin-degrading enzyme, carboxypeptidase B, weakened this vascular reaction. Results described indicate that the permeability-enhancing reaction induced by the protease is caused by activation, of the kallikrein-kinin cascade in the tissue.

Role of bradykinin in microbial infection: enhancement of septicemia by microbial proteases and kinin

Data presented herein will show that bradykinin, microbial proteases which activate the kinin generating cascade, and kininase inhibitors can enhance septicemia by approximately 10 to 100 fold in mice infected intraperitoneally (i.p.) with a strain of bacteria, Pseudomonas aeruginosa 621, which does not usually produce a kinin generating protease. Bacterial spreading was evaluated either in the blood or in the spleen by colony formation on agar plates. Using the P. aeruginosa kaguma strain which produces a large amount of proteases, further experiments were carried out. Results showed that two different protease inhibitors (ovomacroglobulin and a synthetic peptide inhibitor against pseudomonal elastase) as well as a kinin antagonist suppressed bacterial dissemination to 1/10-1/100 of control. Similar results were observed in experiments using Vibrio vulnificus. These data support the hypothesis that microbial proteases and especially bradykinin is responsible for facilitation of microbial dissemination in vivo.

Interaction of Pseudomonas aeruginosa with human lung fibroblasts: role of bacterial elastase

Colonization of cell surfaces by Pseudomonas aeruginosa is mediated by bacterial adherence, which, in turn, is influenced by both host and microbial factors. Previous studies with this organism suggest that elastase contributes to tissue invasion and necrosis. We studied the effects of Pseudomonas elastase (PE) on the adherence of P. aeruginosa to human lung fibroblast monolayers. Treatment of fibroblasts with PE (1 microgram/ml or 0.06 U/ml) increased adherence of 35S-labeled P. aeruginosa to cells, but heat-inactivated PE did not affect bacterial adhesion. Immunocytochemistry of cultured cells showed that PE (0.06 to 0.63 U/ml) decreased fibronectin (Fn) on the cell surface and extracellular matrix of cultured human lung fibroblasts. Data obtained by cytofluorography indicated that elastase also decreased Fn receptors on fibroblasts. Additional evidence for Fn degradation was provided by SDS-PAGE analysis of soluble Fn and proteins from surface iodinated cell monolayers treated with PE. We conclude that the increased bacterial adherence to fibroblasts may be due, in part, to elastase-induced proteolysis of Fn and its receptors on cell surfaces. Degradation of Fn could thus influence the extent and course of Pseudomonas infection in the lungs.

Purification and properties of the elastase from Aspergillus fumigatus

Elastase, a potential virulence factor from the opportunistic pathogen Aspergillus fumigatus, was purified 220-fold from culture broth by fast-performance liquid chromatography employing anion exchange (Q Sepharose fast flow), cation exchange (S Sepharose fast flow), and gel filtration (Superose 12). Purified to near homogeneity, the elastase had an apparent molecular mass of 32 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (silver stain) but a mass of about 19.1 kDa as determined by gel filtration on Superdex 75. The elastase is not glycosylated and is positively charged at neutral pH, having a pI of 8.75. Inhibition by 0.2 mM phenylmethylsulfonyl fluoride (100%) and 0.21 mM leupeptin (60%) implies that the elastase is a serine protease. However, the enzyme is also inhibited by 5 mM EDTA (100%) and 10 mM 1,10-orthophenanthroline (30%), suggesting a requirement for divalent cations. The enzyme acts optimally at pH 7.4 and 45 degrees C in 50 mM sodium borate buffer, but in Tris HCl, the pH optimum shifts to 8.8.

Vascular permeability enhancement by Vibrio mimicus protease and the mechanisms of action

Vibrio mimicus, a causative agent of gastroenteritis, has also been reported to attribute to extraintestinal infections. Recently we have purified a metalloprotease produced by the pathogen: however, the role of the protease in V. mimicus infection has not been documented. The V. mimicus protease (VMP) was found to enhance vascular permeability and form edema when injected into the dorsal skin of guinea pig and rat. The permeability enhancement by VMP was observed in a dose-dependent manner in both guinea pig and rat skin. In guinea pig, an inhibitor of the angiotensin-converting enzyme was found to augment the permeability enhancement reaction. The permeability enhancement was significantly blocked by soybean trypsin inhibitor (SBTI), an inhibitor of plasma kallikrein reaction. In vitro conversion of plasma prekallikrein to kallikrein by VMP was also noted. In rat skin, the permeability enhancement reaction was not blocked by antihistamine or SBTI. However, the reaction was partially blocked when a mixture of antihistamine and SBTI was administered with VMP. It is apparent from the study that in guinea pig skin, VMP enhances vascular permeability through activation of plasma kallikrein-kinin system which generates bradykinin, whereas in addition to the activation of plasma kallikrein-kinin cascade in the case of rat, stimulation of histamine release from mast cells and other unknown mechanism seem to be also a cause of the permeability enhancement reaction. These results suggest that VMP may play a role in extraintestinal infections with edema caused by the pathogen.

Effects of protease inhibitors on growth of Serratia marcescens and Pseudomonas aeruginosa

The growth inhibitory effects of chicken egg white ovomacroglobulin (ovoM) on Serratia marcescens and Pseudomonas aeruginosa were studied. The growth of protease-producing strains was greater than that of the strains producing little protease, and was inhibited in a dose-dependent manner by ovoM, a potent protease inhibitor. Dose-dependent enhancement of growth of strains of S. marcescens and P. aeruginosa that produce little protease was observed with the medium treated with proteases. These results indicate that extracellular proteases produced by the organisms augment their growth and that inhibition of the proteases results in suppression of growth.

Serratia infections in patients with neutropenia

We report on six cases of sepsis caused by Serratia marcescens in patients with neutropenia. Four cases showed an additional involvement of the upper respiratory and digestive tract with oral and pharyngeal mucositis, haemorrhagic laryngo-tracheo-bronchitis, and oedematous swelling of the face. One patient showed a Serratia marcescens carrier state in the pharynx over a period of months without neutropenia. The isolated strains showed a broad spectrum of resistance against antibiotics; only aztreonam and amikacin were effective in vitro against all isolates.

Kinin-generating cascade in advanced cancer patients and in vitro study

The role of the bradykinin-generating system in the pathogenesis of cancer was explored by simultaneously measuring plasma prekallikrein (PK), the precursor of kallikrein, which is the major enzyme responsible for kinin generation, and plasma kininogens (KNG), which are precursors of kinin, in patients with various cancers. The mean value of plasma PK in healthy volunteers was 2.5 +/- 0.5 (mean +/- SD) units/mg plasma protein and that in cancer patients (all stage IV) was 1.7 +/- 0.7 units/mg plasma protein. The mean value of plasma KNG in healthy volunteers was 12.5 +/- 2.0 ng kinin equivalents/mg plasma protein and that in cancer patients was 10.9 +/- 2.8 ng. These data showed that plasma PK and plasma KNG values were significantly lower in cancer patients compared with healthy volunteers (P less than or equal to 0.005 for PK; 0.0005 less than P less than or equal to 0.005 for KNG; n = 28 for healthy subjects; n = 29 for cancer patients). These data appear to indicate that conversion of PK to kallikrein would probably occur with concomitant consumption of KNG by newly generated kallikrein for kinin generation in cancer patients. Early stage cancer patients showed little difference from healthy volunteers. For the in vitro study, activation of purified Hageman factor (HF) and PK was examined by using cancer cell lines and virus-transformed cells that produced plasminogen activator (PA) at a high rate. Both HF and PK were activated in the presence of plasminogen. Diploid cell lines and primary fibroblasts, which did not produce PA, activated neither HF nor PK. Taking all these data together, we conclude that kinin generation does occur in the plasma of patients with advanced cancer, and that one of the initiation mechanisms of the kinin-generating cascade appears to be mediated by plasmin and to depend on cancer cell-derived PA activity.

Triggering of the vascular permeability reaction by activation of the Hageman factor-prekallikrein system by house dust mite proteinase

A 30-kilodalton (kDa) proteinase from the house dust mite Dermatophagoides farinae (Df-proteinase) was recently purified (Takahashi et al. (1990) Int. Arch. Allergy Appl. Immunol. 91, 80-85). In this paper we detailed the biological activities of the Df-proteinase. The activation of the kinin cascade by Df-proteinase was examined in vitro by using purified guinea pig Hageman factor (HF), prekallikrein (PK) and high-molecular-weight kininogen (HMWK) and the effect of this proteinase on endogenous human plasma proteinase inhibitors (serpins) and alpha 2-macroglobulin was tested. In addition, enhancement of the vascular permeability reaction in guinea pig skin by Df-proteinase was examined in vivo. These experiments showed that Df-proteinase could activate all the steps of the kinin-generating cascade, i.e., HF, PK and HMWK, and that Df-proteinase retained proteolytic activity even in the presence of an excess amount of endogenous proteinase inhibitors in plasma. We also found that the marked enhancement of the vascular permeability reaction was induced by Df-proteinase via the activation of the kinin-generating cascade without the release of histamine. From these results, we conclude that the proteinase of the house dust mite, Df-proteinase, has the potential to generate bradykinin and that the presence of this proteinase in biological systems would exacerbate inflammatory reactions in some pathological conditions.

Inactivation of chemotactic activity of C5a by the serratial 56-kilodalton protease

The effects of the 56-kilodalton protease (56K protease) from Serratia marcescens on complement-derived chemotactic activity were examined. Fresh human serum was incubated with zymosan to produce C5a. This activated serum was then incubated with various concentrations of 56K protease, and the chemotactic activity of mouse peritoneal exudate polymorphonuclear leukocytes (PMN) and macrophages was evaluated. A significant dose-dependent decrease of chemotactic activity was observed after protease treatment. Furthermore, treatment of human recombinant C5a with 56K protease at a dose of 1.0 microgram/ml resulted in a complete loss of chemotactic activity. When the living bacteria of the virulent strain, which produced about 10 times more protease than did the less virulent strain, were injected intraperitoneally into mice, the magnitude of infiltration of polymorphonuclear leukocytes into the peritoneal cavity was much lower than that caused by the less virulent strain. Because complement-dependent chemotactic activity is an initial response to bacterial infection, these results suggest indirect pathogenic functions of serratial proteases that suppress chemotactic activity.