Secreted neutral metalloproteases of Bacillus anthracis as candidate pathogenic factors

To evaluate the pathogenic potential of Bacillus anthracis-secreted proteases distinct from lethal toxin, two neutral zinc metalloproteases were purified to apparent homogeneity from the culture supernatant of a non-virulent delta Ames strain (pXO1-, pXO2-). The first (designated Npr599) is a thermolysin-like enzyme highly homologous to bacillolysins from other Bacillus species. The second (designated InhA) is a homolog of the Bacillus thuringiensis immune inhibitor A. These proteases belong to the M4 and M6 families, respectively. Both enzymes digested various substrates, including extracellular matrix proteins, endogenous inhibitors, and coagulation proteins, with some differences in specificity. In addition, InhA accelerated urokinase-mediated plasminogen activation, suggesting that InhA acts as a modulator of plasmin in the host inflammatory system. Relevant to epithelial barrier function, Npr599 and InhA significantly enhanced syndecan-1 shedding from cultured normal murine mammary gland cells without affecting their viability through stimulation of the host cell ectodomain shedding mechanism. In addition, Npr599 and InhA directly cleaved recombinant syndecan-1 fused to glutathione S-transferase. Mass spectrometric analysis suggested that the cleavage sites of Npr599 and InhA are the Asp(39)-Asp(40) and Gly(48)-Thr(49) bonds, respectively. We propose that Npr599 and InhA from B. anthracis are multifunctional pathogenic factors that may contribute to anthrax pathology through direct degradation of host tissues, increases in barrier permeability, and/or modulation of host defenses.

Venom gland EST analysis of the saw-scaled viper, Echis ocellatus, reveals novel α9β1 integrin-binding motifs in venom metalloproteinases and a new group of putative toxins, renin-like aspartic proteases

Echis ocellatus is the most medically important snake in West Africa. However, the composition of its venom and the differential contribution of these venom components to the severe haemorrhagic and coagulopathic pathology of envenoming are poorly understood. To address this situation we assembled a toxin transcriptome based upon 1000 expressed sequence tags (EST) from a cDNA library constructed from pooled venom glands of 10 individual E. ocellatus. We used a variety of bioinformatic tools to construct a fully annotated venom-toxin transcriptome that was interrogated with a combination of BLAST annotation, gene ontology cataloguing and disintegrin-motif searching. The results of these analyses revealed an unusually abundant and diverse expression of snake venom metalloproteinases (SVMP) and a broad toxin-expression profile including several distinct isoforms of bradykinin-potentiating peptides, phospholipase A(2), C-type lectins, serine proteinases and l-amino oxidases. Most significantly, we identified for the first time a conserved alpha(9)beta(1) integrin-binding motif in several SVMPs, and a new group of putative venom toxins, renin-like aspartic proteases.

Vipera lebetina venom contains all types of snake venom metalloproteases

Snake venoms contain four classes of metalloproteases that all have a typical zinc-chelating sequence (HEXXHGXXH). N-terminal sequences and internal sequences of different purified metalloproteases were determined using Edman sequencing and LC MS/MS technique. Oligonucleotides were designed and used as primers for cDNA cloning from Vipera lebetina venom gland cDNA library. We found that isoforms of fibrinolytic enzyme lebetase Le-4 and Le-3 are synthesized in different way: Le-4 is synthesized as P-I type metalloprotease, Le-3 is synthesized with disintegrin-like domain as P-II type protease and processed post-translationally. An endothelial cell apoptosis-inducing heterodimeric glycosylated metalloprotease, V. lebetina apoptosis-inducing protease (VLAIP), belongs to P-III type containing metalloprotease, disintegrin-like and cysteine-rich domains. All these enzymes hydrolyze the Aalpha-chain and more slowly the Bbeta-chain of fibrinogen. Treatment of HUVEC cells with VLAIP induces changes in the attachment of cells to the substrate and causes apoptosis. V. lebetina venom contains also P-IV type-specific coagulant factor X activator (VLFXA) that cleaves the Arg52-Ile53 bond in the heavy chain of human factor X. VLFXA is a glycoprotein composed of a heavy chain and two C-type lectin-like light chains linked by disulfide bonds. The heavy and light chains of VLFXA are synthesized from different genes.

Some aspects of the venom proteome of the Colubridae snakePhilodryas olfersiirevealed from a Duvernoy's (venom) gland transcriptome

We investigated the putative toxins of Philodryas olfersii (Colubridae), a representative of a family of snakes neglected in venom studies despite their growing medical importance. Transcriptomic data of the venom gland complemented by proteomic analysis of the gland secretion revealed the presence of major toxin classes from the Viperidae family, including serine proteases, metalloproteases, C-type lectins, Crisps, and a C-type natriuretic peptide (CNP). Interestingly, the phylogenetic analysis of the CNP precursor showed it as a linker between two related precursors found in Viperidae and Elapidae snakes. We suggest that these precursors constitute a monophyletic group derived from the vertebrate CNPs.

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.

Superactivation of the botulinum neurotoxin serotype A light chain metalloprotease: a new wrinkle in botulinum neurotoxin

Small molecules based upon a 2-acylguanidine-5-phenyl thiophene scaffold that can activate the light chain metalloprotease of botulinum neurotoxin serotype A (BoNT LC/A) by an apparent reduction in Km are reported. On the basis of structure-activity relationships and the activation profile, one or more molecules of activator specifically bind to a defined site on the toxin, causing the observed rate enhancement. With the ever-growing clinical uses of BoNT, compounds such as those reported here may provide a method for combating the emerging adaptive immune responses to BoNT.

Molecular Analysis of Ulilysin, the Structural Prototype of a New Family of Metzincin Metalloproteases

The metzincin clan encompasses several families of zinc-dependent metalloproteases with proven function both in physiology and pathology. They act either as broad spectrum protein degraders or as sheddases, operating through limited proteolysis. Among the structurally uncharacterized metzincin families are the pappalysins, of which the most thoroughly studied member is human pregnancy-associated plasma protein A (PAPP-A), a heavily glycosylated 170-kDa multidomain protein specifically cleaving insulin-like growth factor (IGF)-binding proteins (IGFBPs). Proulilysin is a 38-kDa archaeal protein that shares sequence similarity with PAPP-A but encompasses only the pro-domain and the catalytic domain. It undergoes calcium-mediated autolytic activation, and the mature protein adopts a three-dimensional structure with two subdomains separated by an active site cleft containing the catalytic zinc ion. This structure is reminiscent of human members of the adamalysin/ADAMs (a disintegrin and a metalloprotease) family of metzincins. A bound dipeptide yields information on the substrate specificity of ulilysin, which specifically hydrolyzes IGFBP-2 to -6, insulin, and extracellular matrix proteins but not IGFBP-1 or IGF-II. Accordingly, ulilysin has higher proteolytic efficiency and a broader substrate specificity than human PAPP-A. The structure of ulilysin represents a prototype for the catalytic domain of pappalysins.

Pseudallescheria boydii releases metallopeptidases capable of cleaving several proteinaceous compounds

Pseudallescheria boydii is an opportunistic filamentous fungus that causes serious infections in humans. Virulence attributes expressed by P. boydii are unknown. Conversely, peptidases are incriminated as virulence factors in several pathogenic fungi. Here we investigated the extracellular peptidase profile in P. boydii. After growth on Sabouraud for 7 days, mycelia of P. boydii were incubated for 20 h in PBS-glucose. The cell-free PBS-glucose supernatant was submitted to SDS-PAGE and 12 secretory polypeptides were observed. Two of these polypeptides (28 and 35 kD) presented proteolytic activity when BSA was used as a copolymerized substrate. The extracellular peptidases were most active in acidic pH (5.5) and fully inhibited by 1,10-phenanthroline, a zinc-metallopeptidase inhibitor. Other metallo-, cysteine, serine and aspartic proteolytic inhibitors did not significantly alter these activities. To confirm that these enzymes belong to the metallo-type peptidases, the apoenzymes were obtained by dialysis against chelating agents, and supplementation with different cations, especially Cu(2+) and Zn(2+), restored their activities. Except for gelatin, both metallopeptidases hydrolyzed various co-polymerized substrates, including human serum albumin, casein, hemoglobin and IgG. Additionally, the metallopeptidases were able to cleave different soluble proteinaceous substrates such as extracellular matrix components and sialylated proteins. All these hydrolyses were inhibited by 1,10-phenanthroline. Interestingly, Scedosporium apiospermum (the anamorph of P. boydii) produced a distinct extracellular peptidase profile. Collectively, our results demonstrated for the first time the expression of acidic extracellular metallopeptidases in P. boydii capable of degrading several proteinaceous compounds that could help the fungus to escape from natural human barriers and defenses.

Control of ErbB signaling through metalloprotease mediated ectodomain shedding of EGF-like factors

Epidermal growth factor (EGF)-like proteins comprise a group of structurally similar growth factors, which contain a conserved six-cysteine residue motif called the EGF-domain. EGF-like factors are synthesized as transmembrane precursors, which can undergo proteolytic cleavage at the cell surface to release a mature soluble ectodomain; a process often referred to as "ectodomain shedding". Ectodomain shedding of EGF-like factors has been linked to multiple zinc-binding metalloproteases of the matrix metalloprotease (MMP) and a disintegrin and metalloprotease (ADAM) families. Shedding can be activated by a variety of pharmacological and physiological stimuli and these activation events have been linked to the enhancement of metalloprotease activity, possibly via the action of intracellular signaling modules. Once shed from the cell surface, EGF-like factors bind to a family of four cell surface receptors named ErbB-1, -2, -3 and -4. Heterodimerization or homodimerization of these receptors following ligand binding drives intracellular signal transduction cascades, which eventuate in diverse cell fates including proliferation, differentiation, migration and inhibition of apoptosis. In addition to its role in driving normal developmental processes, a wealth of evidence now exists showing that de-regulated ErbB signaling is associated with the formation of tumors in a variety of tissues and that ectodomain shedding of EGF-like factors plays a critical event in this process. Thus, knowledge of the molecular mechanisms by which EGF-like factors are shed from the cell surface and the nature of the proteases and cellular signals that govern this process is crucial to understanding ErbB receptor signaling and potentially also in the development of novel cancer therapeutics targeting the ErbB pathway. This review focuses on the structure and function of EGF-like factors, and the mechanisms that govern the shedding of these transmembrane molecules from the cell surface.

Molecular dynamics simulation of Leishmania major surface metalloprotease GP63 (leishmanolysin)

One of the molecular factors contributing to Leishmania sp. virulence and pathogenesis is the major surface metalloprotease GP63, alternatively called leishmanolysin, MSP, and PSP (EC 3.4.24.36). Here, the molecular dynamics simulation of Leishmania major GP63 in water at pH 7 is reported. Upon solvation, GP63 undergoes a sharp structural relaxation with respect to the crystal structure. The fluctuation pattern occurs essentially in solvent-exposed nonstructured regions. By contrast, the active site turns out to be rigid. Essential dynamics and dynamic-domain analyses, both carried out on the equilibrated portion of GP63, show that the fingerprint fluctuations of GP63 are practically characterized by the motion of a large part of the N-terminal domain. These results appear to be in line with substrate recognition and (pro)enzyme activation played by the N-terminal domain of GP63. A systematic analysis among a series of 10 homologs of GP63 also shows that the residues involved in the interdomain bending result highly conserved. This finding also suggests possible relationship between the maintainance of proteolytic activity and the similarity of the dynamical properties of the related enzymes.

Mammalian Tolloid Alters Subcellular Localization, Internalization, and Signaling of α1a-Adrenergic Receptors

In the present study, we identified the CUB5 domain of mammalian Tolloid (mTLD) as a novel protein binding to alpha(1A)-adrenergic receptor (AR) using the yeast two-hybrid system. Whereas CUB5 did not couple to either alpha(1B)-AR or alpha(1D)-AR. It was determined that amino acids 322 to 359 of alpha(1A)-AR were the major binding region for CUB5. The direct interaction between alpha(1A)-AR cytoplasmic tail and CUB5 was discovered by glutathione S-transferase pull-down assay. We confirmed the interaction of mTLD with alpha(1A)-AR in human embryonic kidney (HEK) 293 cells by immunoprecipitation, immunofluorescence, and fluorescence resonance energy transfer. Although mTLD did not affect the density and affinity of receptors in crudely prepared membranes from HEK293 cells stably expressing alpha(1A)-AR, it significantly altered the subcellular localization of the receptors. Moreover, mTLD reduced the level of cell surface alpha(1A)-ARs, delayed the initial rate of agonist-induced receptor internalization, and facilitated agonist-induced calcium transient. We have demonstrated that mTLD interacts with alpha(1A)-AR directly, alters the subcellular localization of receptor, and influences agonist-induced alpha(1A)-AR internalization and calcium signaling.

Identification and properties of proteases from an Acanthamoeba isolate capable of producing granulomatous encephalitis

BACKGROUND

Granulomatous amoebic encephalitis due to Acanthamoeba is often a fatal human disease. However, the pathogenesis and pathophysiology of Acanthamoeba encephalitis remain unclear. In this study, the role of extracellular Acanthamoeba proteases in central nervous system pathogenesis and pathophysiology was examined.

RESULTS

Using an encephalitis isolate belonging to T1 genotype, we observed two major proteases with approximate molecular weights of 150 KD and 130 KD on SDS-PAGE gels using gelatin as substrate. The 130 KD protease was inhibited with phenylmethylsulfonyl fluoride (PMSF) suggesting that it is a serine protease, while the 150 KD protease was inhibited with 1, 10-phenanthroline suggesting that it is a metalloprotease. Both proteases exhibited maximal activity at neutral pH and over a range of temperatures, indicating their physiological relevance. These proteases degrade extracellular matrix (ECM), which provide structural and functional support to the brain tissue, as shown by the degradation of collagen I and III (major components of collagenous ECM), elastin (elastic fibrils of ECM), plasminogen (involved in proteolytic degradation of ECM), as well as casein and haemoglobin. The proteases were purified partially using ion-exchange chromatography and their effects were tested in an in vitro model of the blood-brain barrier using human brain microvascular endothelial cells (HBMEC). Neither the serine nor the metalloprotease exhibited HBMEC cytotoxicity. However, the serine protease exhibited HBMEC monolayer disruptions (trypsin-like) suggesting a role in blood-brain barrier perturbations.

CONCLUSION

Overall, these data suggest that Acanthamoeba proteases digest ECM, which may play crucial role(s) in invasion of the brain tissue by amoebae.

MSTF: a domain involved in bacterial metallopeptidases and surface proteins, mycobacteriophage tape-measure proteins and fungal proteins

Here we report a novel domain, MSTF (domain involved in bacterial metallopeptidases, surface proteins and other proteins, also present in mycobacteriophage tape-measure proteins and fungal proteins), which is present in bacteria, phages and fungi. MSTF is about 67-94 amino acids in length with one HxDHxH motif and some highly conserved residues including His, Gly, Ala and Asp. Secondary structure prediction indicated that this domain contains two alpha-helices and one beta-sheet. Identification of MSTF will provide an opportunity to develop new strategies to combat pathogenic microorganisms, especially Mycobacterium tuberculosis.

Isolation and characterization of cotiaractivase, a novel low molecular weight prothrombin activator from the venom of Bothrops cotiara

In this study, we isolated a novel prothrombin activator from the venom of Bothrops cotiara, a Brazilian lance-headed pit viper (Cotiara, Jararaca preta, Biocotiara), which we have designated "cotiaractivase" (prefix: cotiar- from B. cotiara; suffix: -activase, from prothrombin activating activity). Cotiaractivase was purified using a phenyl-Superose hydrophobic interaction column followed by a Mono-Q anion exchange column. It is a single-chain polypeptide with a molecular weight of 22,931 Da as measured by mass spectroscopy. Cotiaractivase generated active alpha-thrombin from purified human prothrombin in a Ca2+-dependent manner as assessed by S2238 chromogenic substrate assay and SDS-PAGE. Cotiaractivase cleaved prothrombin at positions Arg271-Thr272 and Arg320-Ile321, which are also cleaved by factor Xa. However, the rate of thrombin generation by cotiaractivase was approximately 60-fold less than factor Xa alone and 17 x 10(6)-fold less than the prothrombinase complex. The enzymatic activity of cotiaractivase was inhibited by the chelating agent EDTA, whereas the serine protease inhibitor PMSF had no effect on its activity, suggesting that it is a metalloproteinase. Interestingly, S2238 inhibited cotiaractivase activity non-competitively, suggesting that this toxin contains an exosite that allows it to bind prothrombin independently of its active site. Tandem mass spectrometry and N-terminal sequencing of purified cotiaractivase identified peptides that were identical to regions of the cysteine-rich and disintegrin-like domains of known snake venom metalloproteinases. Cotiaractivase is a unique low molecular weight snake venom prothrombin activator that likely belongs to the metalloproteinase family of proteins.

Mammalian Tolloid-like 1 Binds Procollagen C-proteinase Enhancer Protein 1 and Differs from Bone Morphogenetic Protein 1 in the Functional Roles of Homologous Protein Domains

Bone morphogenetic protein 1 (BMP1) is the prototype of a subgroup of metalloproteinases with manifold roles in morphogenesis. Four mammalian subgroup members exist, including BMP1 and mammalian Tolloid-like 1 (mTLL1). Subgroup members have a conserved protein domain structure: an NH2-terminal astacin-like protease domain, followed by a fixed order of CUB and epidermal growth factor-like protein-protein interaction motifs. Previous structure/function studies have documented those BMP1 protein domains necessary for secretion, and activity against various substrates. Here we demonstrate that, in contradiction to previous reports, the most NH2-terminal CUB domain (CUB1) is not required for BMP1 secretion nor is the next CUB domain (CUB2) required for enzymatic activity. The same is true for mTLL1. In fact, secreted protease domains of BMP1 and mTLL1, devoid of CUB or epidermal growth factor-like domains, have procollagen C-proteinase (pCP) activity and activity for biosynthetic processing of biglycan, the latter with kinetics superior to those of the full-length proteins. Structure-function analyses herein also suggest differences in the functional roles played by some of the homologous domains in BMP1 and mTLL1. Surprisingly, although BMP1 has long been known to be Ca2+-dependent, a property previously assumed to apply to all members of the subgroup, mTLL1 is demonstrated to be independent of Ca2 levels in its ability to cleave some, but not all, substrates. We also show that pCP activities of only versions of BMP1 and mTLL1 with intact COOH termini are enhanced by the procollagen C-proteinase enhancer 1 (PCOLCE1) and that mTLL1 binds PCOLCE1, thus suggesting reappraisal of the accepted paradigm for how PCOLCE1 enhances pCP activities.

Inflammatory effects of BaP1 a metalloproteinase isolated from Bothrops asper snake venom: leukocyte recruitment and release of cytokines

The inflammatory events induced by BaP1, a 22.7 kDa metalloproteinase isolated from Bothrops asper snake venom, were studied. BaP1 i.p. injection in mice induced a marked inflammatory cell infiltrate into peritoneal cavity of animals with predominance of neutrophils in the early phase followed by mononuclear cells in the late period. Inhibition of enzymatic activity of BaP1 by chelation with EDTA resulted in a drastic reduction of this effect. In addition, BaP1 induced a significant increase of blood neutrophil numbers before its accumulation in peritoneal cavity, thus suggesting a stimulatory action of BaP1 on mechanisms of cell mobilization from bone marrow reserve compartments. A reduction in the number of neutrophils was observed in the exudate when antibodies against LECAM-1, CD18 and LFA-1 were used, suggesting the involvement of these adhesion molecules in the effects of BaP1. In contrast, there was no effect with antibodies against ICAM-1 and PECAM-1. Moreover, a conspicuous increment in the levels of IL-1 and TNF-alpha, but not of LTB4, was observed in peritoneal washes collected from mice injected with BaP1. It is concluded that BaP1 induces in vivo a marked leukocyte influx, which parallels an increased number of these cells in the blood, and is associated to the expression of specific leukocyte adhesion molecules and release of chemotactic inflammatory cytokines. Since BaP1 is a P-I class metalloproteinase, these results indicate that the proteolytic domain of metalloproteinases per se can trigger specific inflammatory events.

Pulsed EPR investigations of systems modeling molybdenum enzymes: hyperfine and quadrupole parameters of oxo-17O in [Mo 17O(SPh)4]-

Ka band ESEEM spectroscopy was used to determine the hyperfine (hfi) and nuclear quadrupole (nqi) interaction parameters for the oxo-17O ligand in [Mo 17O(SPh)4]-, a spectroscopic model of the oxo-Mo(V) centers of enzymes. The isotropic hfi constant of 6.5 MHz found for the oxo-17O is much smaller than the values of approximately 20-40 MHz typical for the 17O nucleus of an equatorial OH(2) ligand in molybdenum enzymes. The 17O nqi parameter (e2qQ/h = 1.45 MHz, eta approximately = 0) is the first to be obtained for an oxo group in a metal complex. The parameters of the oxo-17O ligand, as well as other magnetic resonance parameters of [Mo 17O(SPh)4]- predicted by quasi-relativistic DFT calculations, were in good agreement with those obtained in experiment. From the electronic structure of the complex revealed by DFT, it follows that the SOMO is almost entirely molybdenum d(xy) and sulfur p, while the spin density on the oxo-17O is negative, determined by spin polarization mechanisms. The results of this work will enable direct experimental identification of the oxo ligand in a variety of chemical and biological systems.

Snake venom metalloproteases--structure and function of catalytic and disintegrin domains

Snake venoms are relevant sources of toxins that have evolved towards the engineering of highly active compounds. In the last years, research efforts have produced great advance in their understanding and uses. Metalloproteases with disintegrin domains are among the most abundant toxins in many Viperidae snake venoms. This review will focus on the structure, function and possible applications of the metalloprotease and disintegrin domains.

Mutational analysis of the potential catalytic residues of the VV G1L metalloproteinase

The vaccinia virus G1L open-reading frame is predicted to be a metalloproteinase based upon the presence of a conserved zinc-binding motif. Western blot analysis demonstrates G1L undergoes proteolytic processing during the course of infection, although the significance of this event is unknown. In order to determine which amino acid residues are important for G1L activity, a plasmid-borne library of G1L constructs containing mutations in and about the active site was created. Transient expression analysis coupled with a trans complementation assay of a conditionally-lethal mutant virus suggest that, of the mutants, only glutamic acid 120 is non-essential for G1L processing to occur.

Overexpression and mechanistic characterization of blastula protease 10, a metalloprotease involved in sea urchin embryogenesis and development

Blastula protease 10 (BP10) is a metalloenzyme involved in sea urchin embryogenesis, which has been assigned to the astacin family of zinc-dependent endopeptidases. It shows greatest homology with the mammalian tolloid-like genes and contains conserved structural motifs consistent with astacin, tolloid, and bone morphogenetic protein 1. Astacin, a crustacean digestive enzyme, has been proposed to carry out hydrolysis via a metal-centered mechanism that involves a metal-coordinated "tyrosine switch." It has not been determined if the more structurally complex members of this family involved in eukaryotic development share this mechanism. The recombinant BP10 has been overexpressed in Escherichia coli, its metalloenzyme nature has been confirmed, and its catalytic properties have been characterized through kinetic studies. BP10 shows significant hydrolysis toward gelatin both in its native zinc-containing form and copper derivative. The copper derivative of BP10 shows a remarkable 960% rate acceleration toward the hydrolysis of the synthetic substrate N-benzoyl-arginine-p-nitroanilide when compared with the zinc form. The enzyme also shows calcium-dependent activation. These are the first thorough mechanistic studies reported on BP10 as a representative of the more structurally complex members of astacin-type enzymes in deuterostomes, which can add supporting data to corroborate the metal-centered mechanism proposed for astacin and the role of the coordinated Tyr. We have demonstrated the first mechanistic study of a tolloid-related metalloenzyme involved in sea urchin embryogenesis.

Cloning of two novel P-III class metalloproteinases from Trimeresurus stejnegeri venom gland

Hemorrhagic toxins are widely distributed in viperid and crotalid snake venoms. Envenomation of Trimeresurus stejnegeri, a member of Crotalidae family, caused potent systemic and local hemorrhage. Up to now, there is no report on hemorrhage toxins from this venom. In this work, we cloned two cDNAs of P-III metalloproteinase precursors, designated as stejnihagin-A and stejnihagin-B, respectively, from T. stejnegeri venom gland. Both cDNAs encode an opening reading frame of 600 amino acid residues, containing a signal sequence, a proprotein domain, a metalloproteinase domain, a disintegrin-like domain and a cystetine-rich domain. Sequence analysis suggested that these two sequences shared highest similarity to the hemorrhagic toxin HR1b from T. flavoviridis. Aligning the deduced mature protein sequences of stejnihagin-A and stejnihagin-B with other snake venom metalloproteinases (SVMPs), we observed that stejnihagin-A and stejnihagin-B, together with HR1b shared the common cysteinyl residue at the position 100 in the metalloproteinase domain. In combination with the phylogenetic analysis, we presumed that stejnihagin-A, stejnihagin-B and HR1b might constitute a novel subclass of P-III SVMPs, named P-IIIc.

The molecular architecture of the metalloprotease FtsH

The ATP-dependent integral membrane protease FtsH is universally conserved in bacteria. Orthologs exist in chloroplasts and mitochondria, where in humans the loss of a close FtsH-homolog causes a form of spastic paraplegia. FtsH plays a crucial role in quality control by degrading unneeded or damaged membrane proteins, but it also targets soluble signaling factors like sigma(32) and lambda-CII. We report here the crystal structure of a soluble FtsH construct that is functional in caseinolytic and ATPase assays. The molecular architecture of this hexameric molecule consists of two rings where the protease domains possess an all-helical fold and form a flat hexagon that is covered by a toroid built by the AAA domains. The active site of the protease classifies FtsH as an Asp-zincin, contrary to a previous report. The different symmetries of protease and AAA rings suggest a possible translocation mechanism of the target polypeptide chain into the interior of the molecule where the proteolytic sites are located.

NMR solution structure of Thermotoga maritima protein TM1509 reveals a Zn-metalloprotease-like tertiary structure

The 150-residue protein TM1509 is encoded in gene YF09_THEMA of Thermotoga maritima. TM1509 has so far no functional annotation and belongs to protein family UPF0054 (PFAM accession number: PF02130) which contains at least 146 members. The NMR structure of TM1509 reveals an alpha+beta fold comprising a four stranded beta-sheet with topology A( upward arrow), B( upward arrow), D( upward arrow), C( downward arrow) as well as five alpha-helices I-V. The structures of most members of family PF02130 can be reliably constructed using the TM1509 NMR structure, demonstrating high leverage for exploration of fold space. A multiple sequence alignment of TM1509 with homologues of family UPF0054 shows that three polypeptide segments, as well as a putative zinc-binding consensus motif HGXLHLXGYDH located at the C-terminal end of alpha-helix IV, are highly conserved. The spatial arrangement of the three His residues of this UPF0054 consensus motif is similar to the arrangement found for the His residues in the HEXXHXXGXXH zinc-binding consensus motif of matrix metallo-proteases (MMPs). Moreover, the other conserved polypeptide segments form a large cavity which encloses the putative Zn-binding pocket and might confer specificity during catalysis. However, TM1509 and the other members of the UPF0054 family do not have the crucial Glu residue in position 2 of the MMP consensus motif. Intriguingly, the TM1509 structure indicates that the Asp in the UPF0054 consensus motif (Asp 111 in TM1509) may overtake the catalytic role of the Glu. This suggests that protein family UPF0054 might contain members of a hitherto uncharacterized class of metalloproteases.

Expression, purification and molecular modeling of recombinant fibrinogenase [IV], a metalloproteinase from Deinakistrodon acutus venom

A novel metalloproteinase, recombinant fibrinogenase IV (rFIV(a)), was expressed and purified from Deinakistrodon acutus venom. It was a single chain protein with an apparent molecular weight 27 kDa and an isoeletric point of pH 7.1. RFIV(a) cleaved preferentially the Aalpha-chain and also cleaved Bbeta, gamma-chains of fibrinogen when the incubation time was prolonged. The proteolytic activity was inhibited by EDTA, l-cysteine, and DTT, indicating rFIV(a) was a metalloproteinase requiring disulfide bonds for its activity. It kept above 85% of the initial activity from pH 4.5-11, showed an equal maximum activity at the temperature range from 30 to 50 degrees C, and was inactivated by Zn2+, Cu2+ and Cd2+. Homology modeling of rFIV(a) showed that two highly conserved disulfide bonds (Cys159-Cys164 and Cys117-Cys197) was maintained from its structure, and it exhibited the characteristic conserved motif H142E143XXH146XXGXXH152, whose three histidine residues were involved in binding of the catalytically essential zinc ion. This work demonstrates the expression, purification and characterization of recombinant fibrinogenase IV, which belongs to class P-I metalloproteinase from D. acutus venom.

Characterization of excretory/secretory endopeptidase and metallo-aminopeptidases from Taenia crassiceps metacestodes

Cysticercosis is caused by Taenia spp. metacestodes, which must survive in the host tissues to complete their life cycle. Their survival depends on their control of host immune responses. Because many parasites use proteases to modulate host responses, we examined culture media from Taenia crassiceps metacestodes for protease activity using peptide substrates. We identified prominent aminopeptidase activity at neutral pH, which was inhibited by chelating agents and partially inhibited by the aminopeptidase inhibitor, bestatin. Endopeptidase substrates were optimally cleaved at slightly acidic pH and endopeptidase activity was inhibited by cysteine protease inhibitors. Gel filtration FPLC and subsequent visualization by silver staining revealed a metallo-aminopeptidase of molecular weight 21 kDa and cysteine proteases of Mr 70 and 64 kDA. Recombinant IL-2 was digested when incubated with parasite culture supernatants, but not with control media. IL-2 degradation was completely inhibited by 1,10 phenanthroline and partially inhibited by bestatin, suggesting that a metallo-aminopeptidase was responsible. Incubation of human IgG with culture supernatants resulted in complete degradation of IgG, which was blocked by cysteine protease inhibitors. These observations demonstrate that Taenia spp. metacestodes secrete a number of proteolytic enzymes, which may target molecules from the host immune system and assist in evasion of the host immune response.

Potent histamine-releasing activity of atrahagin, a novel snake venom metalloproteinase

Poisonous snakebite wound is a popular disease worldwide. However, the pathogenesis remains unclear. In the present study, a novel metalloproteinase atrahagin in Chinese cobra (Naja atra) snake venom was purified, using heparin-sepharose followed by Superdex 75 gel filtration chromatography. Apart from its alpha-fibrinogenase activity, atrahagin potently activated human colon, lung and tonsil mast cells with the net histamine release being 25.9+/-4.4, 17.0+/-1.9, 13.2+/-3.6%, respectively. Time course studies revealed that the peak histamine release induced by atrahagin occurred at 12, 12 and 8 min following incubation of the enzyme with colon, lung and tonsil mast cells, respectively. The response of mast cells to atrahagin was abolished by preincubation of the cells with metabolic inhibitors or pertussis toxin, and by removal of Ca2+ and Mg2+ from the challenge buffer. In conclusion, activation of human mast cells by atrahagin indicated that the enzyme might contribute to the pathogenesis of snakebite wound.

Functional roles of the two distinct domains of halysase, a snake venom metalloprotease, to inhibit human platelet aggregation

Halysase, a hemorrhagic metalloprotease, has an apparent molecular weight of 66kDa and belongs to the class P-III snake venom metalloprotease. Class P-III snake venom metalloproteases have multifunctional domains including a protease domain and a disintegrin-like domain. Halysase was able to preferentially hydrolyze the alpha-chain of fibrinogen. Proteolytic activity of the enzyme was completely inhibited by metal chelating agents but not by other typical protease inhibitors. The enzyme principally cleaves X-Leu, X-Tyr, X-Phe, and X-Ala peptide bonds of the oxidized insulin B-chain. Halysase strongly suppresses collagen-induced human platelet aggregation in a dose-dependent manner. Apohalysase that is devoid of its metalloprotease activity was also able to inhibit the platelet aggregation to a certain extent. Experimental evidence clearly indicates that each of the two distinct domains of halysase, the metalloprotease and the disintegrin-like domains, plays its characteristic role to inhibit human platelet aggregation.

Identification of candidate substrates for ectodomain shedding by the metalloprotease-disintegrin ADAM8

ADAM proteases are type I transmembrane proteins with extracellular metalloprotease domains. As for most ADAM family members, ADAM8 (CD156a, MS2) is involved in ectodomain shedding of membrane proteins and is linked to inflammation and neurodegeneration. To identify potential substrates released under these pathologic conditions, we screened 10-mer peptides representing amino acid sequences from extracellular domains of various membrane proteins using the ProteaseSpot system. A soluble ADAM8 protease containing a pro- and metalloprotease domain was expressed in E. coli and purified as active protease owing to autocatalytic prodomain removal. From 34 peptides tested in the peptide cleavage assay, significant cleavage by soluble ADAM8 was observed for 14 peptides representing membrane proteins with functions in inflammation and neurodegeneration, among them the beta-amyloid precursor protein (APP). The in vivo relevance of the ProteaseSpot method was confirmed by cleavage of full-length APP with ADAM8 in human embryonic kidney 293 cells expressing tagged APP. ADAM8 cleaved APP with similar efficiency as ADAM10, whereas the inactive ADAM8 mutant did not. Exchanging amino acids at defined positions in the cleavage sequence of myelin basic protein (MBP) revealed sequence criteria for ADAM8 cleavage. Taken together, the results allowed us to identify novel candidate substrates that could be cleaved by ADAM8 in vivo under pathologic conditions.

ADAMTS-4 (aggrecanase-1): N-Terminal activation mechanisms

ADAMTS-4 (aggrecanase 1) is synthesized as a latent precursor protein that may require activation through removal of its prodomain before it can exert catalytic activity. We examined various proteinases as well as auto-activation under a wide range of conditions for removal of the prodomain and induction of enzymatic activity. The proprotein convertases, furin, PACE4, and PC5/6 efficiently removed the prodomain through cleavage at Arg(212)/Phe(213), generating an active enzyme. Of a broad range of proteases evaluated, only MMP-9 and trypsin were capable of removing the prodomain. In the presence of mercuric compounds, removal of the prodomain through autocatalysis was not observed, nor was it observed at temperatures from 22 to 65 degrees C, at ionic strengths from 0.1 to 1M, or at acidic/neutral pH. At basic pH 8-10, removal of the prodomain by autocatalysis occurred, generating an active enzyme. In conclusion, the pro-form of ADAMTS-4 is not catalytically active and only a limited number of mechanisms mediate its N-terminal activation.

Purification and characterization of fibrinolytic enzyme from cultured mycelia of Armillaria mellea

A fibrinolytic enzyme was purified from the cultured mycelia of Armillaria mellea by ion-exchange chromatography followed by gel filtration, and was designated A. mellea metalloprotease (AMMP). The purification protocol resulted in a 627-fold purification of the enzyme, with a final yield of 6.05%. The apparent molecular mass of the purified enzyme was estimated to be 21kDa by SDS-PAGE, fibrin-zymography and gel filtration chromatography, which revealed a monomeric form of the enzyme. The optimal reaction pH value and temperature were, pH 6.0, and 33 degrees C, respectively. This protease effectively hydrolyzed fibrinogen, preferentially digesting the Aalpha-chain over the Bbeta- and r-chains. Enzyme activity was inhibited by Cu(2+) and Co(2+), but enhanced by the addition of Ca(2+) and Mg(2+) ions. Furthermore, AMMP activity was potently inhibited by EDTA, and was found to exhibit a higher specificity for the substrate S-2586 for chymotrypsin, indicating that the enzyme is a chymotrypsin-like metalloprotease. The first 24 amino acid residues of the N-terminal sequence were MFSLSSRFFLYTLCL SAVAVSAAP, which is extremely similar to the 24 amino acid residues of the N-terminal sequence of the fruiting body of A. mellea. These data suggest that the fibrinolytic enzyme AMMP, obtained from the A. mellea exhibits a profound fibrinolytic activity. The mycelia of A. mellea may thus represent a potential source of new therapeutic agents to treat thrombosis.

Similarity networks of protein binding sites

An increasing attention has been dedicated to the characterization of complex networks within the protein world. This work is reporting how we uncovered networked structures that reflected the structural similarities among protein binding sites. First, a 211 binding sites dataset has been compiled by removing the redundant proteins in the Protein Ligand Database (PLD) (http://www-mitchell.ch.cam.ac.uk/pld/). Using a clique detection algorithm we have performed all-against-all binding site comparisons among the 211 available ones. Within the set of nodes representing each binding site an edge was added whenever a pair of binding sites had a similarity higher than a threshold value. The generated similarity networks revealed that many nodes had few links and only few were highly connected, but due to the limited data available it was not possible to definitively prove a scale-free architecture. Within the same dataset, the binding site similarity networks were compared with the networks of sequence and fold similarity networks. In the protein world, indications were found that structure is better conserved than sequence, but on its own, sequence was better conserved than the subset of functional residues forming the binding site. Because a binding site is strongly linked with protein function, the identification of protein binding site similarity networks could accelerate the functional annotation of newly identified genes. In view of this we have discussed several potential applications of binding site similarity networks, such as the construction of novel binding site classification databases, as well as the implications for protein molecular design in general and computational chemogenomics in particular.

Crystal structure of a non-hemorrhagic fibrin(ogen)olytic metalloproteinase complexed with a novel natural tri-peptide inhibitor from venom of Agkistrodon acutus

Thrombotic occlusive diseases pose a great threat to human health. Thrombolytic agents are in widespread use for the dissolution of arterial and venous pathologic thrombi in these kinds of diseases. Snake venom metalloproteinases (SVMPs) can act directly on fibrin/fibrinogen and are therefore potential candidates for therapeutic use against thrombotic occlusive diseases. In this study, we have determined the crystal structure of FII, a novel non-hemorrhagic SVMP isolated from Anhui Agkistrodon acutus snake venom by molecular replacement. The structure reveals that FII is a member of the P-I class SVMPs. The Zn2+ ion essential for hydrolytic activity is found in the active site and is tetrahedrally co-ordinated by three histidine residues and water molecule. Unambiguous electron density for a tri-peptide with sequence KNL is also found located near the active site. Biochemical evidences show that the tri-peptide KNL can inhibit the enzymatic activity of FII.

A zymographic study of metalloprotease activities in extracts and extracellular secretions of Leishmania (Viannia) braziliensis strains

Proteolytic activities of 5 strains of Leishmania (Viannia) braziliensis isolated from Brazilian and Colombian patients, presenting distinct clinical manifestations, were characterized and compared using whole-promastigote extracts and extracellular secretions. Zymographic assays concerning whole-cell extracts and supernatants resulted in the detection of high molecular weight bands, ranging from 50 to 125 kDa. Proteolytic activities from both whole-cell extracts and supernatants were optimal in a pH range 5.5 to 9.0 for all analysed strains. Such protease activities were inhibited when 10 mM 1,10-phenanthroline was assayed, strongly suggesting that the enzymes responsible for hydrolysis of the substrate belong to the metalloproteases class. Distinct profiles of metalloproteases were observed among the studied L. (V.) braziliensis strains. Differences among the microorganisms might be related to the geographical origin of the strains and/or to the clinical presentation.

Proteolytic, edematogenic and myotoxic activities of a hemorrhagic metalloproteinase isolated from Bothrops alternatus venom

A hemorrhagic metalloproteinase has been isolated from Bothrops alternatus venom from specimens that inhabit the north-east region of Argentina. The present study aimed at evaluating the proteolytic, hemorrhagic, edematogenic and myotoxic activities of the purified metalloproteinase, in order to consider its participation on the phatophysiology of the intoxication by Bothrops alternatus venom. The hemorrhagic metalloproteinase was isolated by a combination of DEAE-Cellulose chromatography and gel filtration on Sephadex G-75. The enzyme showed a molecular mass around 55k Da, it exhibited a hemorrhagic activity with a minimal hemorrhagic dose of 1.9 microg, almost two fold minor than the whole venom (3.6 microg). The enzyme showed a weak proteolytic activity on casein (18.72 U/mg enzyme), similar to the one exhibited by the whole venom (20 U/mg venom). Besides, the ability to degrade casein could be detected by SDS-PAGE; beta-casein was the fraction that showed the higher degradation, followed by alphas(1)-casein and kappa-casein degradation. The hemorrhagic metalloproteinase rapidly hydrolysed the A alpha-chain of fibrinogen, followed by B beta-chain degradation and leaving the gamma-chain unaffected. Proteolytic activities were inhibited by EDTA whereas they were not inhibited by benzamidine and PMSF. The metalloproteinase showed several polypeptides chains after autocatalytic processing, including a chain of 28k Da, it could be the processed disintegrin-like and cysteine-rich domains. The isolated enzyme exhibited myotoxic activity with high CK levels at 6h, due to local ischemia resulting of its hemorrhagic activity, and a significant edema-inducing effect (MED=1.3 microg), corroborated both results by the histological observations of samples of gastrocnemius muscle. These findings showed that this hemorrhagic metalloproteinase, possesses high edematogenic and myotoxic activities and, in despite of exhibiting a weak proteolytic activity, it is able to degrade fibrinogen. So, this enzyme would contribute markedly to the phatophysiology of the bothropic envenomation.

The Lymantria dispar nucleopolyhedrovirus enhancins are components of occlusion-derived virus

Enhancins are metalloproteinases, first identified in granuloviruses, that can enhance nucleopolyhedrovirus (NPV) potency. We had previously identified two enhancin genes (E1 and E2) in the Lymantria dispar multinucleocapsid NPV (LdMNPV) and showed that both were functional. For this study, we have extended our analysis of LdMNPV enhancin genes through an immunocytochemical analysis of E1 and E2 expression and localization. E1 and E2 peptide antibodies recognized proteins of approximately 84 kDa and 90 kDa, respectively, on Western blots of extracts from L. dispar 652Y cells infected with wild-type virus. The 84- and 90-kDa proteins were first detected at 48 h postinfection (p.i.) and were present through 96 h p.i. E1 and E2 peptide antibodies detected E1 and E2 in polyhedron extracts, and the antibodies were shown to be specific for E1 and E2, respectively, through the use of recombinant virus strains lacking the enhancin genes. E1 and E2 were further localized to occlusion-derived virus (ODV). The enhancins were not found in budded virus. Immunoelectron microscopy indicated that E1 and E2 were present in ODV envelopes and possibly in nucleocapsids. Fractionation studies with several detergents suggested that the enhancins were present in ODV envelopes in association with nucleocapsids. In contrast, enhancins in granuloviruses are located within the granulin matrix. The presence of LdMNPV enhancins within ODV provides a position for the proteins to interact directly on the peritrophic membrane as ODV traverses this host defense barrier.

Plant mitochondria contain at least two i-AAA-like complexes

The FtsH proteases, also called AAA proteases, are membrane-bound ATP-dependent metalloproteases. The Arabidopsis genome contains a total of 12 FtsH-like genes. Two of them, AtFtsH4 and AtFtsH11, encode proteins with a high similarity to Yme1p, a subunit of the i-AAA complex in yeast mitochondria. Phylogenetic analysis groups the AtFtsH4, AtFtsH11 and Yme1 proteins together, with AtFtsH4 being the most similar to Yme1. Using immunological method we demonstrate here that AtFtsH4 is an exclusively mitochondrial protein while AtFtsH11 is found in both chloroplasts and mitochondria. AtFtsH4 and AtFtsH11 proteases are integral parts of the inner mitochondrial membrane and expose their catalytic sites towards the intermembrane space, same as yeast i-AAA. Database searches revealed that orthologs of AtFtsH4 and AtFtsH11 are present in both monocotyledonous and dicotyledonous plants. The two plant i-AAA proteases differ significantly in their termini: the FtsH4 proteins have a characteristic alanine stretch at the C-terminal end while FtsH11s have long N-terminal extensions. Blue-native gel electrophoresis revealed that AtFtsH4 and AtFtsH11 form at least two complexes with apparent molecular masses of about 1500 kDa. This finding implies that plants, in contrast to fungi and metazoa, have more than one complex with a topology similar to that of yeast i-AAA.

Haemophilus paragallinarumsecretes metalloproteases

Haemophilus paragallinarum secretes metalloproteases into different culture media lacking serum. Secreted proteins, concentrated by precipitation with 70% ammonium sulphate ((NH4)2SO4) or methanol, displayed proteolytic activity at >100 kDa molecular mass in 10% polyacrylamide gels co-polymerized with porcine gelatin (0.1%). They were active in a broad pH range (4–9); pH 7.5 being the optimum. Protease activity was inhibited by 20 mmol EDTA/L and reactivated by calcium. The proteolytic activity was heat-stable at 40, 50, and 60 °C, but its activity diminished at 70 °C or higher. Secreted proteins partially degraded chicken immunoglobulin G (IgG) and cross-reacted with a polyclonal serum against a high molecular mass protease secreted by Actinobacillus pleuropneumoniae. Extracellular proteases could play a role in infectious coryza caused by H. paragallinarum.Key words: pathogenicity, secreted protein, infectious coryza.

Deciphering cryptic proteases

Proteases are deeply involved in physiology and pathology. For most, the mechanism is well defined but several fail to display typical protease features (as is the case of the four proteases contained in fibronectin, the inhibitor-resistant mesotrypsin and the proteosomal deubiquitinating enzyme) or have unclear physiological function (such as calpain-like proteins, transthyretin and factor seven activating protease). In other cases, such as in peroxisomal processing proteases, although substrates are defined, the enzyme remains undiscovered. Furthermore, several proteases were identified in pathological conditions, namely secretases in Alzheimer's disease and gross cystic disease fluid protein 15 kDa in breast cancer, when most likely their physiological substrate is still hidden. Lastly, the evolutionary conservation of proteolytic enzymes raises questions related to the origin of biological events, such as the origin of cystein proteases and cell death responses. In this review we will discuss the above cryptic enzymes, as they will probably be relevant in the future.

Purification and characterization of a solvent stable protease from Pseudomonas aeruginosa PseA

A solvent tolerant Pseudomonas aeruginosa PseA strain was isolated from soil. It secreted a novel alkaline protease, which was stable and active in the presence of range of organic solvents, thus potentially useful for catalysis in non-aqueous media. The protease was purified 11.6-fold with 60% recovery by combination of ion exchange and hydrophobic interaction chromatography using Q-Sepharose and Phenyl Sepharose 6 Fast Flow matrix, respectively. The apparent molecular mass based on the sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was estimated to be 35,000 Da. The enzyme was stable in the pH range of 6.0-9.0, the optimum being 8.0. The Km and Vmax towards caseinolytic activity were found to be 2.7 mg/ml and 3 micromol/min, respectively. The protease was most active at 60 degrees C and characterized as a metalloprotease because of its sensitivity to EDTA and 1,10-phenanthroline. It was tested positive for elastase activity towards elastin-orcein, thus appears to be an elastase, which is known as pseudolysin in other strains of P. aeruginosa. The protease withstands range of detergents, surfactants and solvents. It is stable and active in all the solvents having log P above 3.2, at least up to 72 h. These two properties make it an ideal choice for applications in detergent formulations and enzymatic peptide synthesis.

Enhanced peptide secretion by gene disruption of CYM1, a novel protease in Saccharomyces cerevisiae

Saccharomyces cerevisiae is a widely used host in the production of therapeutic peptides and proteins. Here we report the identification of a novel endoprotease in S. cerevisiae. It is encoded by the CYM1 gene and is specific for the C-terminus of basic residues of heterologously expressed peptides. Gene disruption of CYM1 not only reduced the intracellular proteolysis, but also enhanced the secretion of heterologously expressed peptides such as growth hormone, pro-B-type natriuretic peptide and pro-cholecystokinin. Cym1p resembles metalloendoproteases of the pitrilysin family with the HXXEH(X)E(71-77) catalytic domain as seen in insulysin, nardilysin and human metalloprotease 1. It is a nuclear encoded protease that localizes to mitochondria without a hydrophobic N-terminal signal sequence or a C-terminal tail-anchor. The protease does not require post-translational processing prior to activation and it contains cytosolic activity that processes peptides designated for the secretory pathway prior to translocation into the endoplasmic reticulum.

Snake Venom Metalloproteinase Containing a Disintegrin-like Domain, its Structure-activity Relationships at Interacting with Integrins

Snake venom disintegrins represent a family of RGD (Arg-Gly-Asp) or KGD (Lys-Gly-Asp)-containing proteins which have been reported to be unique and potentially useful tools not only for investigating integrin-ligand interactions, but also for the development of anti-thrombotic agents in terms of their anti-platelet activities. Snake venom proteins containing a disintegrin-like domain represent another super-family of proteins in which many of them have been demonstrated to have similar ability to inhibit platelet aggregation and integrin-mediated cell adhesion as the disintegrins. This super-family includes a large number of snake venom metalloproteinases and disintegrin related, RGD-containing snake venom proteins (disintegrin-like proteins) such as dendroaspin. Recently, a family of homologues of the snake venom metalloproteinases have been found in a wide variety of mammalian tissues as well as in other eukaryotic organisms termed ADAM (a disintegrin-like and metalloproteinase) proteins. ADAMs are members of the metazincins that also include the related matrix metalloprotease (MMPs). Some of ADAM proteins have now shown to interact with integrins, and the disintegrin-like domain may be crucial part in their function as proteases. A description of structure-activity relationships of snake venom proteins containing a disintegrin-like domain is outlined in this review, along with reports of the modulation of protein activity by recombinant mutation. Comparison is also made of the structural and functional features of the metalloproteinases in snakes compared with those from other species. The review is intended to provide insights in which may assist the development of new therapeutic approaches.

A novel metalloprotease from Vipera lebetina venom induces human endothelial cell apoptosis

A novel endothelial cell apoptosis inducing metalloprotease (VLAIP) was found in the snake venom of Vipera lebetina. This metalloprotease is a heterodimeric glycoprotein with molecular mass of about 106 kDa. The protease hydrolyzes azocasein, fibrinogen and oxidized insulin B-chain. The enzyme readily hydrolyzes the Aalpha-chain and more slowly Bbeta-chain of fibrinogen. VLAIP does not cleave fibrin. The complete amino acid sequences of the two different monomers of VLAIP are deduced from the nucleotide sequences of cDNAs encoding these proteins. The full-length cDNA sequences of the VLAIP-A and VLAIP-B encode open reading frames of 616 and 614 amino acids that include signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. VLAIP belongs to the metalloprotease/disintegrin family of reprolysins and has high identity with the proteins that induce apoptosis of endothelial cells. Treatment of HUVEC cells with VLAIP induces changes in the attachment of cells to the substrate and causes cell death. We demonstrated that VLAIP inhibits endothelial cell adhesion to extracellular matrix proteins: fibrinogen, fibronectin, vitronectin, collagen I, and collagen IV. The induction of apoptosis by VLAIP was shown by means of a typical DNA fragmentation pattern of apoptotic cells as well as by monitoring phosphatidylserine externalization using annexin V-FITC staining and flow cytometric analysis.

Primary structure and antiplatelet mechanism of a snake venom metalloproteinase, acurhagin, from Agkistrodon acutus venom

Acurhagin has been characterized as a P-III hemorrhagic metalloproteinase. We herein report the complete sequence of acurhagin by molecular cloning. Analysis of the cDNA-predicted amino acid sequence encoding acurhagin precursor revealed that this mosaic Asn-linked glycoprotein possesses a multidomain structure including a proprotein, a metalloproteinase, a disintegrin-like and a cysteine-rich domains (189/205/102/114 residues), with an overall 87% identity to that of jararhagin, an integrin alpha2beta1-cleaving metalloproteinase. Acurhagin has a Ser-Glu-Cys-Asp sequence in the disintegrin-like domain instead of the typical Arg-Gly-Asp motif. In contrast to inhibiting fibrinogen-integrin alphaIIbbeta3 interaction by disintegrins, acurhagin selectively showed a dose-dependent inhibition on platelet aggregation induced by collagen, and suppression on tyrosine phosphorylation of several signaling proteins in convulxin-stimulated platelets. Although the immobilized acurhagin was shown to bind platelet GPVI and collagen in a primary structure- and steric conformation-dependent manner, respectively, the mechanism of acurhagin under short incubation is mainly through its binding to GPVI and collagen, instead of binding to alpha2beta1, or cleaving platelet membrane glycoproteins. Moreover, the molecular conformation maintained by divalent cations is required for the proteolytic activity of acurhagin toward extracellular matrix fibronectin. Taken together, these results suggest that all the three domains in mature acurhagin may cooperatively contribute to its biological function.

Identification and characterization of human archaemetzincin-1 and -2, two novel members of a family of metalloproteases widely distributed in Archaea

Systematic analysis of degradomes, the complete protease repertoires of organisms, has demonstrated the large and growing complexity of proteolytic systems operating in all cells and tissues. We report here the identification of two new human metalloproteases that have been called archaemetzincin-1 (AMZ1) and archaemetzincin-2 (AMZ2) to emphasize their close relationship to putative proteases predicted by bioinformatic analysis of archaeal genomes. Both human proteins contain a catalytic domain with a core motif (HEXXHXXGX3CX4CXMX17CXXC) that includes an archetypal zinc-binding site, the methionine residue characteristic of metzincins, and four conserved cysteine residues that are not present at the equivalent positions of other human metalloproteases. Analysis of genome sequence databases revealed that AMZs are widely distributed in Archaea and vertebrates and contribute to the defining of a new metalloprotease family that has been called archaemetzincin. However, AMZ-like sequences are absent in a number of model organisms from bacteria to nematodes. Phylogenetic analysis showed that these enzymes have undergone a complex evolutionary process involving a series of lateral gene transfer, gene loss, and genetic duplication events that have shaped this novel family of metalloproteases. Northern blot analysis showed that AMZ1 and AMZ2 exhibit distinct expression patterns in human tissues. AMZ1 is mainly detected in liver and heart whereas AMZ2 is predominantly expressed in testis and heart, although both are also detectable at lower levels in other tissues. Both human enzymes were produced in Escherichia coli, and the purified recombinant proteins hydrolyzed synthetic substrates and bioactive peptides, demonstrating that they are functional proteases. Finally, these activities were abolished by inhibitors of metalloproteases, providing further evidence that AMZs belong to this catalytic class of proteolytic enzymes.

Identification and characterization of peptides mimicking the epitopes of metalloprotease of Schistosoma japonicum

In an attempt to isolate and characterize peptides mimicking epitopes of metalloprotease and explore their immunological protection against Schistosoma japonicum (S. japonicum), polyclonal anti-metalloprotease sera was prepared to screen a 12-mer random peptide library to isolate phages binding specially to antisera IgG. Then, phage ELISA, animal immunization, DNA sequencing, Western blotting and enzymatic activity neutralizing analysis were used to characterize the selected phage clones. All of ten randomly picked clones were shown to be positive. Five peptides of different amino acid sequences deduced from DNA sequences were obtained and two of them (peptides 2 and 3) could induce significant reduction (31.0% and 31.8%, respectively) in worm burden and high reduction (52.6% and 54.9%, respectively) in liver eggs per gram (LEPG), while, unexpectedly, others (peptides 1, 4 and 5) could not elicit enough protection against infection of S. japonicum. Peptides 2 and 3 could be recognized by S. japonicum infected mouse sera (IMS) and could elicit neutralizing Abs. The results show that peptides 2 and 3 are antigenic and immunogenic. They are true mimics of epitopes of metalloprotease and useful as novel vaccine candidates against S. japonicum.

A cold-active extracellular metalloprotease from Pedobacter cryoconitis—production and properties

An extracellular protease from Pedobacter cryoconitis, isolated from alpine cryoconite on glacier ice, was purified and characterized. Despite high cell densities at a temperature range of 1-25 degrees C, the optimum temperature for protease production was 15 degrees C. Maximum enzyme production was achieved when the strain was grown in a pH-neutral medium containing soybean meal, wheat flour and citrate over 72 h. The 27-kDa enzyme was a metalloprotease (sensitive to EDTA, EGTA and phenanthroline) and showed maximal activity towards azocasein at 40 degrees C and pH 8. The protease was stable for 60 min at 20-30 degrees C, lost 50% of activity after 30 min at 40 degrees C, and was inactivated at 50 degrees C, but was resistant to repeated freezing and thawing. Calcium ions had no protective effect against thermal denaturation. More than 80% of the maximum activity were retained at a pH in the range of 7-10. No activity loss was detected after 1 h at pH 7-9 and 20 degrees C, nor after 1 h of incubation with 3 M urea or 0.1% perborate.

Cloning, expression and characterization of a 46.5-kDa metallopeptidase from Bacillus halodurans H4 sharing properties with the pitrilysin family

A 1242 base pair DNA fragment from Bacillus halodurans H4 isolated from alkaline sediments of Lake Bogoria (Kenya) coding for a potential protease was cloned and sequenced. The hexa-histidine-tagged enzyme was overexpressed in Escherichia coli and was purified in one step by immobilized-metal affinity chromatography (IMAC) on Ni-NTA resin. The protease (ppBH4) presents an inverted zincin motif, HXXEH, which defines the inverzincin family. It shares several biochemical and molecular properties with the clan ME family M16 metallopeptidases (pitrilysins), as well as with database hypothetical proteins that are potential M16 family enzymes. Thus, like insulysin and nardilysin, but contrary to bacterial pitrilysin, ppBH4 is inactivated by sulfhydryl alkylating agents. On the other hand, like bacterial pitrilysin, ppBH4 is sensitive to reducing agents. The enzymatic activity of ppBH4 is limited to substrates smaller than proteins. In contrast to insulin, dynorphin and insulin B-chain are very good substrates for ppBH4 and several cleavage sites are common with those observed with well-characterized pitrilysins. As deduced from amino acid sequence, as well as determined by gel-filtration and SDS-polyacrylamide gel electrophoresis, ppBH4 is an active monomer of 46.5 kDa. This feature distinguishes ppBH4 from all other enzymes of the pitrilysin family so far described whose molecular masses range from 100 to 140 kDa.

Crystallization and preliminary X-ray studies of a non-haemorrhagic fibrin(ogen)olytic metalloproteinase from the venom of Agkistrodon acutus

A non-haemorrhagic fibrin(ogen)olytic metalloproteinase from the venom of Agkistrodon acutus has been crystallized by the hanging-drop method. The crystals belong to space group P3(1)21, with unit-cell parameters a = b = 80.57, c = 66.77 A and one molecule in the asymmetric unit. X-ray diffraction data were collected to 1.86 A resolution.

Molecular cloning, functional expression, and molecular modeling of bothrostatin, a new highly active disintegrin from Bothrops jararaca venom

Disintegrins are among the most potent antagonists of several integrins. A cDNA encoding a novel disintegrin, bothrostatin, was cloned from a Bothrops jararaca cDNA library. The precursor of bothrostatin contains a pro, a metalloproteinase, and an RGD-disintegrin domain. The disintegrin domain expressed in Escherichia coli showed high inhibitory activity on collagen-induced platelet aggregation (IC(50) of 12nM), and thus it can be used as a useful tool for studies of integrin-ligand interaction. Furthermore, we used the comparative modeling approach to obtain a model of the 3D structure of bothrostatin. Our results suggest that bothrostatin adopts a globular, closed structure in solution. The RGD motif is exposed to the solution by the loop formed by residues 45-59 and is very close to the C-terminal domain forming a finger-like structure. The proximity of the RGD loop and the C-terminal residues, which is maintained by the Cys47-Cys66 bond, suggests that the C-terminal residues are involved in the ability of bothrostatin to interact with its ligands.