Families of zinc metalloproteases

Extracellular cysteines define ectopeptidase (APN, CD13) expression and function

Alanyl aminopeptidase (APN) is a surface-bound metallopeptidase that processes the N-terminals of biologically active peptides such as enkephalins, angiotensins, neurokinins, and cytokines. It exerts profound activity on vital processes such as immune response, cellular growth, and blood pressure control. Inhibition of either APN gene expression or its enzymatic activity severely affects leukocyte growth and function. We show here that oxidoreductase-mediated modulations of the cell surface thiol status affect the enzymatic activity of APN. Additional evidence for the pivotal role of extracellular cysteines in the APN molecule was obtained when substitution of any of these six cysteines caused complete loss of surface expression and enzymatic activity. In contrast, the transmembrane Cys24 appears to have no similar function. Enzymatically inactive cysteine mutants were retained in the endoplasmic reticulum as shown by high-resolution imaging and Endoglycosidase H digestion. In the absence of any crystal-structure data, the demonstration that individual extracellular cysteines contribute to APN expression and function appears to be of particular importance. The data are the first to show thiol-dependent modulation of the activity of a typical surface-bound peptidase at the cell surface, probably reflecting a general regulating mechanism. This may relate to various disease processes such as inflammation or malignant transformation.

Altered regulation of matrix metalloproteinase-2 in aortic remodeling during aging

To elucidate potential mechanisms of enhanced type 2 matrix metalloprotease levels and activity within the thickened aged rat aorta, the present study measured its mRNA and protein levels and those of its membrane bound activator, MT1-MMP, its endogenous tissue inhibitor, TIMP-2, tissue type, and urokinase plasminogen activators and their receptors, and an inhibitor of plasminogen activation in aortae from Fisher 344X Brown Norway rats, 2 to 30 months of age. Semiquantitative immunohistochemistry, in situ hybridization, and in situ zymography of aortae detected a marked age-associated increase in gelatinolytic activity of type 2 metalloprotease within the thickened intima, internal elastic lamina, and elastic fibers in the inner part of the thickened tunica media, whereas the intimal tissue inhibitor of metalloprotease-2 mRNA and protein levels were not age related. Both activators of plasminogen and their receptors increased approximately 2-fold within the intima between 2 to 30 months. Similar, but not identical, age-associated changes in factors that regulate protease activity within the aortic media were also observed. We conclude that discordant regulation of factors that determine the activation status of type 2 matrix metalloprotease, coupled with an increase in the expression of its zymogen, occur with aging, which lead to an increase in the amount of activated protease. These factors are candidate mechanisms for age-associated vascular remodeling, a potent risk factor for vascular diseases with advancing age.

Arg(362) and Tyr(365) of the botulinum neurotoxin type a light chain are involved in transition state stabilization

The botulinum neurotoxin type A (BoNT/A) light chain (LC) acts as zinc endopeptidase. The X-ray structure of the toxin demonstrated that Zn(2+) is coordinated by His(222) and His(226) of the Zn(2+) binding motif HisGluXXHis and Glu(261), whereas Glu(223) coordinates the water molecule required for hydrolysis as the fourth ligand. Recent analysis of a cocrystal of the BoNT/B LC and its substrate synaptobrevin 2 suggested that Arg(362) and Tyr(365) of the homologous BoNT/A may be directly involved in catalysis. Their role and that of Glu(350) which is also found in the vicinity to the active site were analyzed by site-directed mutagenesis. Various replacements of Arg(362) and substitution of Tyr(365) with Phe resulted in 79- and 34-fold lower k(cat)/K(m) values, respectively. These changes were provoked by decreased catalytic rates (k(cat)) and not by alterations of ground state substrate binding as evidenced by largely unchanged K(d) and K(m) values. None of these mutations affected the overall secondary structure or zinc content of the LC. These findings suggest that the guanidino group of Arg(362) and the hydroxyl group of Tyr(365) together accomplish transition state stabilization as was proposed for thermolysin, being the prototypical member of the gluzincin superfamily of metalloproteases. Mutation of Glu(350) dramatically diminished the hydrolytic activity which must partly be attributed to an altered active site fine structure as demonstrated by an increased sensitivity toward heat-induced denaturing and a lower Zn(2+) binding affinity. Glu(350) apparently occupies a central position in the active site and presumably positions His(222) and Arg(362).

Identification of glutamic acid 479 as the gluzincin coordinator of zinc in FtsH (HflB)

Escherichia coli FtsH (HflB) is a membrane-bound and ATP-dependent metalloprotease. Its cytoplasmic domain contains a zinc-binding motif, H(417)EXXH, whose histidine residues have been shown to be functionally important. Although they are believed to be involved directly in zinc coordination, nothing is known about the third zinc ligand of this protease. Sequence alignment indicates that glutamic acid residues are conserved among the FtsH homologues at positions corresponding to Glu(479) and Glu(585) of E. coli FtsH. We replaced each of them by Gln, Asp, Lys, or Val. Mutations at position 479 compromised the proteolytic functions of FtsH in vivo. In vitro proteolytic activities of the E479Q, E479V, and E479D mutant enzymes were much lower than that of the wild-type protein and were significantly stimulated by a high concentration of zinc ion. These mutant proteins retained the wild-type levels of ATPase activities, and their trypsin susceptibilities as well as CD spectra were essentially indistinguishable from those of the wild-type protein, indicating that the mutations did not cause gross conformational changes in FtsH. They exhibited reduced zinc contents upon purification. From these results, we conclude that Glu(479) is a zinc-coordinating residue.

Cloning and characterization of novel extensin-like cDNAs that are expressed during late somatic cell phase in the green alga Volvox carteri

Asexual individuals of the green alga Volvox carteri consist of two cell types, somatic and reproductive cells. The somatic cells are terminally differentiated post-mitotic cells which undergo gradual senescence leading to cell death in every generation. To understand the gene expression programs associated with senescence of somatic cells, we cloned two cDNAs, LSG1 and LSG2, that are preferentially expressed during this late developmental stage. These two cDNAs were deduced to encode Pro-rich motifs characteristic of extensin proteins that are components of the extracellular matrix. LSG1 also resembled genes encoding plant pathogenesis-related protein 1 (PR-1), while LSG2 showed similarities with genes encoding matrix metalloproteinases, including a gamete lytic enzyme of Chlamydomonas. We also found that S9, one of the late somatic cDNAs previously cloned by Tam and Kirk (Dev. Biol. 145 (1991) 51), was deduced to encode a protein with a composition similar to LSG2. The expression of PR-1 and a matrix-metalloproteinase-encoding gene has been shown to be induced during senescence in higher plants. These results indicate that some of the late somatic genes in V. carteri are related to the senescence-associated genes in higher plants.

Molecular characterization of three gut genes from Glossina morsitans morsitans: cathepsin B, zinc-metalloprotease and zinc-carboxypeptidase

Insect gut enzymes are involved in digestion of dietary proteins. Additionally, these enzymes have been implicated in the process of pathogen establishment in several insects including the tsetse fly (Diptera:Glossinidae), which is the vector for African trypanosomes. Both the male and female tsetse can transmit trypanosomes and are strict blood feeders during all stages of their development. Here, we describe the molecular characterization of three gut genes: cathepsin B (GmCatB), zinc-metalloprotease (GmZmp) and zinc-carboxypeptidase (GmZcp). The cDNA for GmCatB encodes a protein for 340 amino acids with a predicted molecular mass of 38.2 kDa, while the 854 bp GmZmp cDNA encodes a protein of 254 amino acids with a molecular mass of 29 kDa. The GmZcp cDNA is 1319 bp in length and has a 354 amino acids open reading frame for coding a 40 kDa protein. All three cDNAs have signal peptide sequences associated with their N-terminal domains and structure analysis indicates that GmCatB and GmZmp are expressed as zymogens with pro-domains proteolytically removed for activity. The activation domain associated with the carboxypeptidase sequences is lacking in GmZcp. While GmCatB transcription is constitutive, teneral flies express very low levels of transcripts for GmZmp and GmZcp prior to the first bloodmeal. Transcription of all genes is induced and remains high throughout the digestion cycle within a few hours following the first bloodmeal ingestion. Both GmCatB and GmZcp are parasite responsive, with the expression of both genes being higher in trypanosome infected flies.

Molecular cloning and characterization of Ac-mep-1, a developmentally regulated gut luminal metalloendopeptidase from adult Ancylostoma caninum hookworms

A zinc metalloendopeptidase cDNA (Ac-mep-1) was cloned from Ancylostoma caninum adult hookworms. Ac-mep-1 is encoded by a 2.8 kb mRNA with a predicted open reading frame (ORF) of 870 amino acids (predicted pI=5.5, m.w.=98.7 kDa) that contains four potential N-linked glycosylation sites and predicted zinc-binding domains (HExxH and ENxADxGG). These domains represent signature sequences of the Neutral Endopeptidase 24.11 (neprilysin) family of enzymes. The ORF corresponding to Ac-MEP-1 exhibited strong similarity to metalloproteases from the trichostrongyle Haemonchus contortus as well as Caenorhabditis elegans. RT-PCR analysis of A. caninum eggs, L1, non-activated and activated L3 and adult cDNA identify transcription of Ac-MEP-1 only in the adult stage of the parasite. Mouse antibody raised to the expressed protein recognized proteins of approximately 90 and 100 kDa in adult hookworm extracts. Adult worm sections probed with these antisera localized Ac-mep-1 to the microvilli of the worm gastrointestinal tract suggesting a possible role for this enzyme in digestion of the parasite blood meal.

Soluble recombinant neprilysin induces aggrecanase-mediated cleavage of aggrecan in cartilage explant cultures

Neprilysin (neutral endopeptidase, enkephalinase, CALLA, CD10, NEP) is a regulatory Zn metallopeptidase expressed in the brush border membranes of the kidney and has been found in porcine chondrocytes and rat articular cartilage as well as other cell types and tissues. Although its function in cartilage is not currently known, previous observations of high levels of NEP enzymatic activity in the synovial fluid of arthritic patients and on the chondrocyte membranes of human osteoarthritic cartilage have led to the hypothesis that NEP is involved in the inflammation or degradation pathways in articular cartilage. Our study localized endogenous NEP to the membranes of mature bovine articular chondrocytes in a tissue explant model and demonstrated that the addition of soluble recombinant NEP (sNEP) to the culture medium of bovine cartilage explants leads to the degradation of aggrecan through the action of aggrecanase. A 6-day exposure to sNEP was necessary to initiate the degradation, suggesting that the chondrocytes were responding in a delayed manner to an altered composition of regulatory peptides. This NEP-induced degradation was completely inhibited by the NEP inhibitors thiorphan and phosphoramidon. These results suggest that NEP is present as a transmembrane enzyme on articular chondrocytes where it can cleave regulatory peptides and lead to the induction of aggrecanase.

Study of asparagine 353 in aminopeptidase A: characterization of a novel motif (GXMEN) implicated in exopeptidase specificity of monozinc aminopeptidases

Aminopeptidase A (EC 3.4.11.7, APA) is a 160 kDa membrane-bound zinc enzyme that contains the HEXXH consensus sequence found in members of the zinc metalloprotease family, the zincins. In addition, the monozinc aminopeptidases are characterized by another conserved motif, GXMEN, the glutamate residue of which has been shown to be implicated in the exopeptidase specificity of aminopeptidase A [Vazeux G. (1998) Biochem. J. 334, 407-413]. In carboxypeptidase A (EC 3.4.17.1, CPA), the exopeptidase specificity is conferred by an arginine residue (Arg-145) and an asparagine residue (Asn-144). Thus, we hypothesized that Asn-353 of the GXMEN motif in APA plays a similar role to Asn-144 in CPA and contributes to the exopeptidase specificity of APA. We investigated the functional role of Asn-353 in APA by substituting this residue with a glutamine (Gln-353), an alanine (Ala-353) or an aspartate (Asp-353) residue by site-directed mutagenesis. Expression of wild-type and mutated APAs revealed that Gln-353 and Ala-353 are similarly routed and glycosylated to the wild-type APA, whereas Asp-353 is trapped intracellularly and partially glycosylated. Kinetic studies, using alpha-L-glutamyl-beta-naphthylamide (GluNA) as a substrate showed that the K(m) values of the mutants Gln-353 and Ala-353 were increased 11- and 8-fold, respectively, whereas the k(cat) values were decreased (2-fold) resulting in a 24- and 14-fold reduction in cleavage efficiency. When alpha-L-aspartyl-beta-naphthylamide or angiotensin II were used as substrates, the mutations had a greater effect on k(cat), leading to a similar decrease in cleavage efficiencies as that observed with GluNA. We then measured the inhibitory potencies of several classes of inhibitors, glutamate thiol, glutamine thiol and two isomers (L- or D-) of glutamate phosphonate to explore the functional role of Asn-353. The data indicate that Asn-353 is critical for the integrity and catalytic activity of APA. This residue is involved in substrate binding via interactions with the free N-terminal part and with the P1 carboxylate side chain of the substrate. In conclusion, Asn-353 of the GXMEN motif, together with Glu-352, contributes to the exopeptidase specificity of APA and plays an equivalent role to Asn-144 in CPA.

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

Vibrio vulnificus, an opportunistic human pathogen, produces a 45-kDa zinc metalloprotease (V. vulnificus protease; VVP) as an important virulence determinant. VVP injected intradermally into the dorsal skin causes the hemorrhagic damage through specific degradation of type IV collage in the vascular basement membrane. The N-terminal 35-kDa polypeptide (VVP-N), the catalytic domain, also evoked the hemorrhagic skin reaction within minutes. However, the hemorrhagic activity of VVP-N was one-third of that of VVP. Besides, the proteolytic activity of VVP-N toward the reconstituted basement membrane or type IV collagen was found to be about 50 % of VVP. VVP-N, like VVP, was quickly inactivated by an equimolar amount of alpha(2)-macroglobulin, a broad-spectrum plasma protease inhibitor. These findings indicate that the C-terminal 10-kDa polypeptide, the substrate-binding domain mediating the effective binding to protein substrates, functions to augment the hemorrhagic reaction of VVP.

The matrix metalloproteinase gene GmMMP2 is activated in response to pathogenic infections in soybean

Matrix metalloproteinases (MMPs) play an important role in host defense responses against pathogens in mammals where their activities lead to the production of antimicrobial peptides. We have identified a novel soybean (Glycine max) metalloproteinase gene, GmMMP2, that is transcriptionally up-regulated in infected tissues. The deduced amino acid sequence indicates that this gene belongs to the MMP family. It is a preproprotein containing an N-terminal signal peptide, a cysteine switch, a zinc-binding catalytic motif, and a C-terminal transmembrane domain. The GmMMP2 expressed in and purified from Escherichia coli exhibited an in vitro enzymatic activity in digesting myelin basic protein. All plant metalloproteinases reported so far have no known functions. However, they have been suggested to be involved in extracellular cell matrix degradation during development or senescence. Our investigations demonstrate that the GmMMP2 transcript levels were rapidly increased in compatible and incompatible interactions of soybean tissues with the oomycete pathogen Phytophthora sojae or the bacterial pathogen Pseudomonas syringae pv. glycinea. In agreement with the GmMMP2 activation, a metalloproteinase activity was gradually increased in suspension-cultured cells following the bacterial infection. GmMMP2 was also activated in response to wounding and dehydration. However, GmMMP2 activation did not correlate with the oxidative burst leading to the hypersensitive response cell death or the tissue senescence progress that involves programmed cell death. Our investigations suggest that GmMMP2 may be involved in a novel defense response of soybean against pathogenic infections.

Biology of TACE inhibition

Studies conducted over the past decade have demonstrated a central role for tumour necrosis factor alpha (TNFalpha) in inflammatory diseases. As a result of this work, a number of biological agents that neutralise the activity of this cytokine have entered the clinic. The recent clinical data obtained with etanercept and infliximab highlight the relevance of this strategy. TNFalpha converting enzyme (TACE) is the metalloproteinase that processes the 26 kDa membrane bound precursor of TNFalpha (proTNFalpha) to the 17 kDa soluble component. Although a number of proteases have been shown to process proTNFalpha, none do so with the efficiency of TACE. A series of orally bioavailable, selective, and potent TACE inhibitors are currently in clinical development. These inhibitors effectively block TACE mediated processing of proTNFalpha and can reduce TNF production by lipopolysaccharide stimulated whole blood by >95%. Through a series of studies it is shown here that >80% of the unprocessed proTNFalpha is degraded intracellularly. The remainder appears to be transiently expressed on the cell surface. Although, in vitro, TACE inhibition has also been implicated in shedding of p55 and p75 surface TNFalpha receptors, the in vivo data cast doubt on the consequences of this finding. In a mouse model of collagen-induced arthritis, the inhibitors are efficacious both prophylactically and therapeutically. The efficacy seen is equivalent to strategies that neutralise TNFalpha. In many studies greater efficacy is observed with the TACE inhibitors, presumably owing to greater penetration to the site of TNFalpha production.

Mannose receptor ligand-positive cells express the metalloprotease decysin in the B cell follicle

Decysin, a gene encoding a disintegrin metalloprotease, is transcribed in human dendritic cells (DC) and germinal centers (GC). We have cloned its murine homologue and show that it is processed by the endoprotease furin before secretion of the catalytic domain. We have defined the cell types that express decysin in mouse spleen in the course of an immune response to T cell-dependent Ags. Like in humans, decysin is transcribed by activated CD11c(+) DC that enter the T cell zone from the marginal zone (MZ). In the GC, decysin is expressed by follicular DC and tingible body macrophages. In addition, a MZ cell population expresses decysin and appears to migrate into the B cell follicle. The majority of these follicle-homing cells express the mannose receptor ligand, a marker for the macrophage-like MZ metallophils. The follicle-homing cells are M-CSF dependent, as they are absent in op/op mice that lack functional M-CSF. This suggests that mannose receptor ligand(+) MZ metallophils differentiate into cells that migrate from the MZ into the B cell follicle. Decysin represents the first marker for this previously unrecognized cell population of the mouse spleen, which may represent a precursor for GCDC and may be specialized in the transport of unprocessed Ag from the MZ into developing GC.

Clostridial hydrolytic enzymes degrading extracellular components

Bacteria belonging to the genus Clostridium, both glycolytic and proteolytic, and both pathogenic and non-pathogenic, produce a battery of hydrolytic enzymes to obtain nutrients from various biopolymers. The clostridial hydrolytic enzymes are diverse, and are used or are potentially useful for fundamental and applied research purposes. Among them, enzymes degrading the major components in the extracellular matrix or on the cell surface in vertebrates are herein reviewed with special emphasis on recent knowledge gained through molecular biology of clostridial collagenases, sialidases and hyaluronidases. This paper also reviews some literature on the biotechnological approach to the designing of new molecular tools and drug delivery systems involving clostridial hydrolytic enzymes.

Isolation and expression of an ecdysteroid-inducible neutral endopeptidase 24.11-like gene in wing discs of Bombyx mori

In the process of comparison of two cDNA libraries (W0, W2), we isolated a clone from the wing discs of Bombyx mori encoding a putative neutral endopeptidase 24.11-like gene. The predicted open reading frame encoded 772 amino acid residues, having about 53% identity with Drosophila GH07643, 36% with rat NEP, and 34% with rat ECE. This is the first NEP gene isolated in invertebrate. A 3.6-kb transcript was found to accumulate in the wing disc according to the increase of ecdysteroid titer during metamorphosis. Accumulation of the transcript was induced in wing discs with 20-hydroxyecdysone about 20h after incubation, which was inhibited by cycloheximide. This gene is ecdysone-inducible, appears to encode a functional protein, and may function during wing metamorphosis.

IGF-binding protein-4 expression and IGF-binding protein-4 protease activity are regulated coordinately in smooth muscle during postnatal development and after vascular injury

Recent studies support a critical role for the paracrine IGF/IGF-binding protein system in the regulation of vascular smooth muscle cell growth. In this study we have explored the hypothesis that the abundance of individual IGF-binding proteins in smooth muscle is subject to regulation during postnatal life and in response to injury. IGF-binding protein-2 was the predominant binding protein secreted by neonatal rat vascular smooth muscle cells, whereas IGF-binding protein-4 was most prevalent in adult vascular smooth muscle cells coincident with increased IGF-binding protein-4 protease activity. After arterial injury, IGF-binding protein-4 mRNA increased, associated with greater IGF-binding protein-4 proteolytic activity, resulting in stable steady state levels of the IGF-binding protein-4 protein. Expression of pregnancy-associated plasma protein A mRNA, recently identified as an IGF-binding protein-4 protease, was expressed at higher levels in adult than neonatal vascular smooth muscle cell lines, but did not change significantly after arterial injury. The peak of immunoreactive pregnancy-associated plasma protein A from hydrophobic interaction chromatography fractions of smooth muscle cell-conditioned medium coincided, but did not fully overlap, with the fractions containing maximal IGF-binding protein-4 protease activity. In conclusion, our data point to a developmental switch from IGF-binding protein-2 to IGF-binding protein-4 in vascular smooth muscle cells postnatally. Moreover, IGF-binding protein-4 expression is coregulated with IGF-binding protein-4 protease activity, suggesting that biosynthesis and degradation of this binding protein are coordinated events important for regulating biological activity of IGF-I.

In vitro cytocidal effects on Trypanosoma brucei and inhibition of Leishmania major GP63 by peptidomimetic metalloprotease inhibitors

Peptidomimetic inhibitors of mammalian zinc metalloproteases have been tested as potential agents for intervention in disease caused by kinetoplastid protozoa. Certain metalloprotease inhibitors were able to inhibit the release of variant surface glycoprotein from cultured transgenic procyclic Trypanosoma brucei, confirming our previous identification of a cell surface zinc metalloprotease activity in this stage of the trypanosome lifecycle [Bangs, JD et al. Expression of bloodstream variant surface glycoproteins in procyclic stage Trypanosoma brucei: role of GPI anchors in secretion, EMBO J. 1997;16:4285]. Selected peptidomimetics were also found to be toxic for cultured bloodstream trypanosomes with IC50 values in the low micromolar range. The paradigm for zinc metalloproteases in kinetoplastids are the GP63 surface enzymes of Leishmania. Peptidomimetics at low micromolar concentrations were able to inhibit in vitro cleavage of a synthetic peptide substrate by purified GP63 from L. major. Our results suggest that zinc metalloproteases perform essential functions in different stages of the trypanosome lifecycle and we hypothesize that these activities may be affected by the recently discovered trypanosomal homologues of GP63 [El-Sayed, NMA and Donelson, JE. African trypanosomes have differentially expressed genes encoding homologues of Leishmania GP63 surface protease, J. Biol. Chem. 1997;272:26742]. Development of higher affinity metalloprotease inhibitors may provide a novel avenue for treatment of parasitic diseases.

Mutational analysis of the thyrotropin-releasing hormone-degrading ectoenzyme. similarities and differences with other members of the M1 family of aminopeptidases and thermolysin

Thyrotropin-releasing hormone-degrading ectoenzyme (TRH-DE) is a TRH-specific peptidase which catalyzes the inactivation of the peptidergic signal substance TRH. As indicated by sequence alignment, TRH-DE and the other members of the M1 family of aminopeptidases have a distinct set of conserved amino acid residues in common. By replacing amino acid residues that are putatively involved in catalysis, we could demonstrate that the enzymatic activities of the mutants E408D, E442D, E464Q, E464D, Y528F, H507R, and H507F are dramatically decreased, essentially due to the changes of V(max). The mutant enzymes E408Q and E442Q are inactive, whereas the specific enzymatic activity of the mutants R488Q, R488A, and Y554F are similar to that of the wild-type enzyme. These data strongly suggest that E408, E442, Y528, and H507 are involved in the catalytic process of TRH-DE while E464 presumably represents the third zinc-coordinating residue and may be equivalent to E166 in thermolysin. In contrast, amino acid residues R488 and Y554 seem not to be involved in the catalytic mechanism of TRH-DE.

Molecular cloning, tissue distribution, and chromosomal localization of MMEL2, a gene coding for a novel human member of the neutral endopeptidase-24.11 family

Members of the neutral endopeptidase (NEP, also known as MME for membrane metallo-endopeptidase in the Human Gene Nomenclature database) family play significant roles in pain perception, arterial pressure regulation, phosphate metabolism, and homeostasis. In this paper, we report the cloning of a new human member of the NEP family that we named MMEL2 for membrane metallo-endopeptidase-like 2. The MMEL2 protein has the structural characteristics of type II transmembrane proteins, although the presence of a furin-like cleavage site in the ectodomain suggests that it may be released into the medium following proteolytic cleavage. The MMEL2 protein contains the zinc-binding consensus sequence HEXXH and all the residues known to be essential for the enzymatic activity of other members of the family. The MMEL2 mRNA was detected predominantly in testis, but weak expression also was observed in brain, kidney, and heart. The human MMEL2 gene was mapped to 1p36 by fluorescence in situ hybridization. It will be important to test whether MMEL2 defects are associated with diseases such as hereditary motor sensory neuropathy 2A, Schwartz-Jampel-Aberfeld syndrome, or neuroblastoma, which all map to this locus.

Lysine aminopeptidase of Aspergillus niger

Conserved regions within the M1 family of metallo-aminopeptidases have been used to clone a zinc aminopeptidase from the industrially used fungus Aspergillus niger. The derived amino acid sequence of ApsA is highly similar to two yeast zinc aminopeptidases, LAPI and AAPI (53.3 and 50.9% overall similarity, respectively), two members of the M1 family of metallo-aminopeptidases. The encoding gene was successfully overexpressed in A. niger and the overexpressed product was purified and characterized. Aminopeptidase A was found to be active towards a number of amino acid p-nitroanilide (pNA) substrates, viz. K-pNA, R-pNA, L-pNA, M-pNA, A-pNA and F-pNA. The most preferred N-terminal amino acid is lysine and not leucine, arginine or alanine, the N-terminal amino acids preferred by the yeast homologues. The K(m) and K(cat) for K-pNA and L-pNA were 0.17 mM and 0.49 microkat mg(-1), and 0.16 mM and 0.31 microkat mg(-1), respectively. The pH optimum of the enzyme is between 7.5 and 8, whereas the enzyme is stable between pH 5 and 8. The enzyme is inhibited by the metal chelators EGTA, EDTA and 1,10-phenanthrolin. Bestatin was also able to inhibit the activity.

Molecular cloning of three cDNAs encoding aminopeptidases from the midgut of Helicoverpa punctigera, the Australian native budworm

Three cDNAs encoding aminopeptidases HpAPN1, HpAPN2 and HpAPN3, were isolated from a 5th instar larval midgut cDNA library from Helicoverpa punctigera, the Australian native budworm. The sequences recovered contain open reading frames encoding proteins of 1011, 952, and 1013 amino acids, respectively. All three proteins share the consensus zinc binding/gluzincin motif HEXXHX(18)E and the sequence GAMEN common to gluzincin aminopeptidases. Furthermore, signal peptide sequences and C-terminal hydrophobic regions preceded by three small amino acids qualifying for cleavage and GPI anchor attachment are present in all three protein sequences. Northern blotting results indicate differences in the levels of expression and developmental regulation of all three aminopeptidases. HpAPN1, HpAPN2, and HpAPN3 are more closely related to APNs from other lepidopterans than they are to each other. This report of three different aminopeptidases N in Helicoverpa punctigera adds support to a recent suggestion that at least one gene duplication has taken place in ancestral lepidopterans. The full sequences of the aminopeptidases are available at GENBANK with the following accession numbers: HpAPN1: AF217248, HpAPN2: AF217249, HpAPN3: AF217250.

Insulin-degrading enzyme: embarking on amyloid destruction

Several human disorders are caused by or associated with the deposition of protein aggregates known as amyloid fibrils. Despite the lack of sequence homology among amyloidogenic proteins, all amyloid fibrils share a common morphology, are insoluble under physiological conditions and are resistant to proteolytic degradation. Because amyloidogenic proteins are being produced continuously, eukaryotic organisms must have developed a form of proteolytic machinery capable of controlling these aggregation-prone species before their fibrillization. This article suggests that an intracellular metalloprotease called insulin-degrading enzyme (IDE) is responsible for the elimination of proteins with amyloidogenic potential and proposes a mechanism for the selectivity of the enzyme. In this respect, IDE can also be referred to as ADE: amyloid-degrading enzyme.

An improved procedure for the generation of recombinant single-chain Fv antibody fragments reacting with human CD13 on intact cells

A procedure was developed to generate recombinant single chain Fv (scFv) antibody fragments reacting with the extracellular domain of human cell surface antigen CD13 (hCD13; aminopeptidase N) on intact cells. Membrane fractions prepared from a stably transfected hCD13-positive murine NIH/3T3 cell line were used to immunize BALB/c mice, with the intention that hCD13 would be the major immunogenic molecule recognized by the immune system. Spleen RNA from the immunized mice served to generate a combinatorial scFv phage display library. The library was adsorbed against non-transfected NIH/3T3 or Sf21 insect cells to eliminate nonrelevant binders. The supernatant was then used for panning with either hCD13-transfected Sf21 insect cells or a hCD13-expressing human leukemia-derived cell line. Therefore, the key concepts of the procedure were the presentation of hCD13 as the sole human antigen on murine NIH/3T3 cells and a screening strategy where hCD13 was the major common antigen of the material used for immunization and panning. Two different hCD13-reactive phages were isolated and the soluble scFvs were expressed in E. coli and purified. The two scFvs, anti-hCD13-1 and anti-hCD13-3, differed at four amino acid positions in their V(H) regions and both had high affinities for hCD13 as determined by surface plasmon resonance (K(D)=7 and 33x10(-10) M, respectively). Both efficiently recognized hCD13 on intact cells. Therefore, the procedure allowed the production of high affinity scFvs reacting with a desired antigen in its native conformation without requiring extensive purification of the antigen and should be useful for the preparation of scFvs against other conformation-sensitive cell-surface antigens.

A proteolytic transmembrane signaling pathway and resistance to beta-lactams in staphylococci

beta-Lactamase and penicillin-binding protein 2a mediate staphylococcal resistance to beta-lactam antibiotics, which are otherwise highly clinically effective. Production of these inducible proteins is regulated by a signal-transducing integral membrane protein and a transcriptional repressor. The signal transducer is a fusion protein with penicillin-binding and zinc metalloprotease domains. The signal for protein expression is transmitted by site-specific proteolytic cleavage of both the transducer, which autoactivates, and the repressor, which is inactivated, unblocking gene transcription. Compounds that disrupt this regulatory pathway could restore the activity of beta-lactam antibiotics against drug-resistant strains of staphylococci.

Single site polymorphisms and alternative splicing of the human CD13 gene--different splicing frequencies among patients with acute myeloid leukaemia and healthy individuals

Within the haematopoietic system, CD13/aminopeptidase N (APN), a transmembrane glycoprotein, is expressed on the surface of early committed progenitors of granulocytes and monocytes and by all cells of these lineages as they mature. CD13 is expressed on the majority of leukaemic myeloblasts in acute myeloid leukaemia (AML), and on leukaemic lymphoblasts in a small percentage of acute lymphoid leukaemia cases. Thus, anti-CD13 monoclonal antibodies are used as diagnostic markers in leukaemia typing. By systematically amplifying overlapping reverse transcription polymerase chain reaction (RT-PCR) amplicons throughout the CD13 mRNA, we identified two splice variants in which exon 3 and exon 14 were lost. Fourteen healthy individuals and 34 patients with AML were screened for these splice variants. All healthy individuals, and the majority of AML patients, had both splice variants but they represented less than 10% of the total RT-PCR-amplified CD13 product. Increased expression of both truncated CD13 mRNA forms were observed in 6% of AML patients, whereas no detectable exon 3 or exon 14 splice variants could be generated in 26% and 9% of AML patients respectively. The different splicing frequencies may reflect altered processing of pre-mRNA or expansion of certain cell types for some AML patients, even though no correlation existed to blast percentage, FAB classification, surface antigens or cytogenetic characteristics. In addition, we identified an intron of 506 bp between exon 1 and exon 2 as well as two sites of single nucleotide polymorphism with a heterozygosity index of about 0.5, making them useful as genetic markers.

Modulation of WNT-5A expression by actinonin: linkage of APN to the WNT-pathway?

Inhibition of alanyl-aminopeptidase gene expression or enzymatic activity compromises T cell proliferation and function. Molecular mechanisms mediating these effects are not known as yet. Applying the cDNA array technique we identified the proto-oncogen Wnt-5a strongly affected by APN-inhibition. Wnt-5a and other members of the Wnt family of secreted factors are implicated in cell growth and differentiation. Wnt-5a was moderately expressed in resting T cells, but strongly down-regulated in response to activation by OKT3/IL-4/IL-9. Actinonin increased Wnt-5a-mRNA contents as confirmed by RT-PCR. In addition, expression of GSK-3 beta, an inherent component of the Wnt-pathway, was found to be increased in response to activation, but suppressed by actinonin at both the mRNA and protein level. These findings may provide a rationale for the strong growth inhibitory effects resulting from an inhibition of alanyl aminopeptidase expression or activity.

Characterisation of a gene cluster involved in bacterial degradation of the cyanobacterial toxin microcystin LR

A novel pathway for degradation of the cyanobacterial heptapeptide hepatotoxin microcystin LR was identified in a newly isolated Sphingomonas sp. (Bourne et al. 1996 Appl. Environ. Microbiol. 62: 4086-4094). We now report the cloning and molecular characterisation of four genes from this Sphingomonas sp. that exist on a 5.8-kb genomic fragment and encode the three hydrolytic enzymes involved in this pathway together with a putative oligopeptide transporter. The heterologously expressed degradation pathway proteins are enzymatically active. Microcystinase (MlrA), the first enzyme in the degradative pathway, is a 336-residue endopeptidase, which displays only low sequence identity with a hypothetical protein from Methanobacterium thermoautotrophicum. Inhibition of microcystinase by EDTA and 1,10-phenanthroline suggests that it is a metalloenzyme. The most likely residues that could potentially chelate an active-site transition metal ion are in the sequence HXXHXE, which would be unique for a metalloproteinase. Situated immediately downstream of mlrA with the same direction of transcription is a gene mlrD, whose conceptual translation (MlrD, 442 residues) shows significant sequence identity and similar potential transmembrane spanning regions to the PTR2 family of oligopeptide transporters. A gene mlrB is situated downstream of the mlrA and mlrD genes, but transcribed in the opposite direction. The gene encodes the enzyme MlrB (402 residues) which cleaves linear microcystin LR to a tetrapeptide degradation product. This enzyme belongs to the "penicillin-binding enzyme" family of active site serine hydrolases. The final gene in the cluster mlrC, is located upstream of the mlrA gene and is transcribed in the opposite direction. It codes for MlrC (507 residues) which mediates further peptidolytic degradation of the tetrapeptide. This protein shows significant sequence identity to a hypothetical protein from Streptomyces coelicolor. It is suspected to be a metallopeptidase based on inhibition by metal chelators. It is postulated on the basis of comparison with other microorganisms that the genes in this cluster may all be involved in cell wall peptidoglycan cycling and subsequently act fortuitously in hydrolysis of microcystin LR.

Identification of critical residues in the active site of porcine membrane-bound aminopeptidase P

The membrane-bound form of mammalian aminopeptidase P (AP-P; EC 3.4. 11.9) is a mono-zinc-containing enzyme that lacks any of the typical metal binding motifs found in other zinc metalloproteases. To identify residues involved in metal binding and catalysis, sequence and structural information was used to align the sequence of porcine membrane-bound AP-P with other members of the peptidase clan MG, including Escherichia coli AP-P and methionyl aminopeptidases. Residues predicted to be critical for activity were mutated and the resultant proteins were expressed in COS-1 cells. Immunoelectrophoretic blot analysis was used to compare the levels of expression of the mutant proteins, and their ability to hydrolyze bradykinin and Gly-Pro-hydroxyPro was assessed. Asp449, Asp460, His523, Glu554, and Glu568 are predicted to serve as metal ion ligands in the active site, and mutagenesis of these residues resulted in fully glycosylated proteins that were catalytically inactive. Mutation of His429 and His532 also resulted in catalytically inactive proteins, and these residues, by analogy with E. coli AP-P, are likely to play a role in shuttling protons during catalysis. These studies indicate that mammalian membrane-bound AP-P has an active-site configuration similar to that of other members of the peptidase clan MG, which is compatible with either a dual metal ion model or a single metal ion in the active site. The latter model is consistent, however, with the known metal stoichiometry of both the membrane-bound and cytosolic forms of AP-P and with a recently proposed model for methionyl aminopeptidase.

The roles of Glu93 and Tyr149 in astacin-like zinc peptidases

The catalytic zinc of astacin, a prototype of the astacin family and the metzincin superfamily of metalloproteinases is coordinated by three histidines, a glutamate bound water and a tyrosine. In order to assess the roles of active site key residues, two mutants, Glu93Ala-astacin and Tyr149Phe-astacin, were expressed in Escherichia coli, affinity-purified and renatured. While the Glu93Ala mutant was inactive, the Tyr149Phe mutant retained about 2. 5% residual activity toward Dns-Pro-Lys-Arg*Ala-Pro-Trp-Val, based on the k(cat)/K(m) value for recombinant wild-type astacin. These results support a model in which Glu93 is the general base in substrate hydrolysis, whereas Tyr149 contributes to transition state binding.

Some molecular and inhibitory specifications of a dipeptidyl carboxypeptidase from the polychaete Neanthes virens resembling angiotensin I converting enzyme

Dipeptidyl carboxypeptidase (DCP) from the polychaete Neanthes virens, resembling mammalian angiotensin I converting enzyme (ACE), was studied to discover some of its molecular and inhibitory properties, as the first evidence of these in a marine invertebrate. Amino acid and carbohydrate contents were analyzed. The N-terminal amino acid sequence of N. virens DCP was (NH2)D-E-E-A-G-R-Q-W-L-A-E-Y-D-L-R-N-Q-T-V-L-. Peptide maps of N. virens DCP from lysyl endopeptidase digestion were different from rabbit p-ACE. The far-ultraviolet circular dichroic spectra of N. virens DCP indicated that the secondary structure of this enzyme seemed to be an alpha-helical structure and was similar to that of rabbit p-ACE, but the near-ultraviolet circular dichroic spectra of N. virens DCP indicated that the aromatic amino acid residue circumambience of this enzyme was different from rabbit p-ACE. The effects of several reagents for chemical modification of amino acids on the activity of N. virens DCP were tested. Arg, Tyr, Glu, and/or Asp, His, Trp, and Met caused loss of the activity. In addition, the IC50 and Ki values for a well-known ACE inhibitor, Val-Tyr, which was a competitive inhibitor of N. virens DCP, were 263 and 20 microM, respectively. These results suggested that N. virens DCP is different from mammalian ACE in the molecular and inhibitory properties, although the same substrate specificity was demonstrated in a previous paper.

A role for a TIMP-3-sensitive, Zn(2+)-dependent metalloprotease in mammalian gamete membrane fusion

During fertilization, sperm and egg plasma membranes adhere and then fuse by a mechanism that is not well understood. Zinc metalloproteases are necessary for some intercellular fusion events, for instance, cell-cell fusion in yeast. In this study we tested the effects of class-specific and family-specific protease inhibitors on mouse gamete fusion. Capacitated, acrosome-reacted sperm and zona-free eggs were used in assays designed to define the effects of inhibitors on sperm-egg plasma membrane binding or fusion. Inhibitors of the aspartic, cysteine, and serine protease classes had no effect on sperm-egg binding or fusion. Both a synthetic metalloprotease substrate (succinyl-Ala-Ala-Phe-amidomethylcoumarin) and the zinc chelator 1,10-phenanthroline inhibited sperm-egg fusion but did not decrease sperm-egg binding. The fusion-inhibition effect of phenanthroline was reversible and activity of the inhibitable zinc metalloprotease was shown to be required during a short time window, the first 15 min after insemination. Tissue inhibitor of metalloprotease-3 and Ro 31-9790, specific inhibitors of zinc metalloproteases in the matrixin and adamalysin families, also inhibited sperm-egg fusion but not sperm-egg binding. These data indicate a role in gamete fusion for one or more zinc metalloproteases of the matrixin and/or adamalysin families that act after plasma membrane binding and before sperm-egg membrane fusion.

Immunoaffinity purification and characterization of native placental leucine aminopeptidase/oxytocinase from human placenta

cDNA cloning of placental leucine aminopeptidase (P-LAP)/cystinyl aminopeptidase (CAP)/oxytocinase demonstrated that this enzyme is a type II integral membrane protein, which means that native P-LAP, found in placenta, is membrane-bound and that the soluble form of this enzyme, found in maternal sera, is most likely derived from the native form. The presence of the different forms of the protein makes it difficult to purify homogeneously. In the current study we prepared antibody specific to native P-LAP and used it to purify native P-LAP from microsomal fractions of human placenta to homogeneity, 5039-fold within 4 h, by immunoaffinity chromatography. Zn(2+)and Cu(2+)strongly inhibited the enzyme but Ca(2+)did not. Amastatin was a more potent inhibitor than bestatin and leupeptin. Using antibodies against native P-LAP, protein having 83 per cent of l -methionine insensitive Leu-p-nitroanilide cleaving activity, was immunoprecipitated from the microsomal fraction of human placenta. The availability of a specific antibody against native P-LAP permits the rapid purification and the preliminary immunoassay of the enzyme. Establishment of simple purification and assay methods for the native, membrane bound form of P-LAP pave the way to elucidating the roles and processing systems of this enzyme.

Snake venom metalloproteinases: their role in the pathogenesis of local tissue damage

The biochemical characteristics of hemorrhagic metalloproteinases isolated from snake venoms are reviewed, together with their role in the pathogenesis of the local tissue damage characteristic of crotaline and viperine snake envenomations. Venom metalloproteinases differ in their domain structure. Some enzymes comprise only the metalloproteinase domain, others have disintegrin-like and high cysteine domains and others present, besides these domains, an additional lectin-like subunit. All of them are zinc-dependent enzymes with highly similar zinc binding environments. Some metalloproteinases induce hemorrhage by directly affecting mostly capillary blood vessels. It is suggested that hemorrhagic enzymes cleave, in a highly selective fashion, key peptide bonds of basement membrane components, thereby affecting the interaction between basement membrane and endothelial cells. As a consequence, these cells undergo a series of morphological and functional alterations in vivo, probably associated with biophysical hemodynamic factors such as tangential fluid shear stress. Eventually, gaps are formed in endothelial cells through which extravasation occurs. In addition to hemorrhage, venom metalloproteinases induce skeletal muscle damage, myonecrosis, which seems to be secondary to the ischemia that ensues in muscle tissue as a consequence of bleeding and reduced perfusion. Microvessel disruption by metalloproteinases also impairs skeletal muscle regeneration, being therefore responsible of fibrosis and permanent tissue loss after snakebites. Moreover, venom metalloproteinases participate in the degradation of extracellular matrix components and play a relevant role in the prominent local inflammatory response that characterizes snakebite envenomations, since they induce edema, activate endogenous matrix metalloproteinases (MMPs) and are capable of releasing TNF-alpha from its membrane-bound precursor. Owing to their protagonic role in the pathogenesis of local tissue damage, snake venom metalloproteinases constitute relevant targets for natural and synthetic inhibitors which may complement antivenoms in the neutralization of these effects.

A novel double-headed proteinaceous inhibitor for metalloproteinase and serine proteinase

A novel proteinaceous inhibitor for the metalloproteinase of Streptomyces caespitosus has been isolated from the culture supernatant of Streptomyces sp. I-355. It was named ScNPI (Streptomyces caespitosus neutral proteinase inhibitor). ScNPI exhibited strong inhibitory activity toward ScNP with a K(i) value of 1.6 nm. In addition, ScNPI was capable of inhibiting subtilisin BPN' (K(i) = 1.4 nm) (EC ). The scnpi gene consists of two regions, a signal peptide (28 amino acid residues) and a mature region (113 amino acid residues, M(r) = 11,857). The deduced amino acid sequence of scnpi showed high similarity to those of Streptomyces subtilisin inhibitor (SSI) and its homologues. The reactive site of ScNPI for inhibition of subtilisin BPN' was identified to be Met(71)-Tyr(72) bond by specific cleavage. To identify the reactive site for ScNP, Tyr(33) and Tyr(72), which are not conserved among other SSI family inhibitors but are preferable amino acid residues for ScNP, were replaced separately by Ala. The Y33A mutant retained inhibitory activity toward subtilisin BPN' but did not show any inhibitory activity toward ScNP. Moreover, a dimer of ternary complexes among ScNPI, ScNP, and subtilisin BPN' was formed to give the 2:2:2 stoichiometry. These results strongly indicate that ScNPI is a double-headed inhibitor that has individual reactive sites for ScNP and subtilisin BPN'.

N-arginine dibasic convertase (nardilysin) isoforms are soluble dibasic-specific metalloendopeptidases that localize in the cytoplasm and at the cell surface

N-arginine (R) dibasic (NRD) convertase (nardilysin; EC 3.4.24.61), a metalloendopeptidase of the M16 family, specifically cleaves peptide substrates at the N-terminus of arginines in dibasic motifs in vitro. In rat testis, the enzyme localizes within the cytoplasm of spermatids and associates with microtubules of the manchette and axoneme. NRD1 and NRD2 convertases, two NRD convertase isoforms, differ by the absence (isoform 1) or presence (isoform 2) of a 68-amino acid insertion close to the active site. In this study, we overexpressed both isoforms, either by vaccinia virus infection of BSC40 cells or transfection of COS-7 cells. The partially purified enzymes exhibit very similar biochemical and enzymic properties. Microsequencing revealed that NRD convertase is N-terminally processed. Results of immunocytofluorescence, immunoelectron microscopy and subcellular fractionation studies argue in favour of a primary cytosolic localization of both peptidases. Although the putative signal peptide did not direct NRD convertase into microsomes in an in vitro translation assay, biotinylation experiments clearly showed the presence of both isoforms at the cell surface. In conclusion, although most known processing events at pairs of basic residues are achieved by proprotein convertases within the secretory pathway, NRD convertase may fulfil a similar function in the cytoplasm and/or at the cell surface.

The mechanisms of platelet dysfunction during extracorporeal membrane oxygenation in critically ill neonates

OBJECTIVE

Although bleeding associated with thrombocytopenia often complicates extracorporeal membrane oxygenation (ECMO), the mechanisms of platelet dysfunction during ECMO remain poorly understood. We investigated the role of matrix metalloproteinase (MMP)-2, which recently has been shown to mediate a novel pathway of platelet aggregation, in the platelet dysfunction induced by ECMO.

DESIGN

Prospective longitudinal case study.

SETTING

Level III neonatal intensive care unit.

PATIENTS

Ten neonates treated with ECMO.

INTERVENTION

ECMO procedure.

MEASUREMENTS

Platelet counts and collagen-induced platelet aggregation ex vivo; plasma markers of platelet (soluble P-selectin) and endothelial (soluble E-selectin and total nitrite/nitrate) activation; plasma MMP-2 and MMP-9 activities; and concentrations of tissue inhibitors of MMPs.

MAIN RESULTS

During ECMO, time-dependent platelet activation, as evidenced by thrombocytopenia, decreased platelet aggregation, and increased plasma soluble P-selectin concentrations were found in the absence of endothelial activation, as shown by normal plasma concentrations of soluble E-selectin and nitric oxide metabolites (nitrite/nitrate). There was a time-dependent increase in plasma MMP-2 but not MMP-9 activity; tissue inhibitors of MMPs were not detected. Plasma soluble P-selectin concentrations significantly correlated with simultaneous plasma MMP-2 (r2 = .37, p < .0001) but not with MMP-9 activities. Platelet dysfunction persisted despite repeated platelet transfusions to maintain platelet counts >100 x 10(9)/L.

CONCLUSIONS

ECMO resulted in the activation of platelets but not endothelial cells. During ECMO, platelet dysfunction persisted despite platelet transfusions. MMP-2 may play a role in the development of platelet dysfunction caused by ECMO.

A matrix metalloproteinase gene is expressed at the boundary of senescence and programmed cell death in cucumber

Cell-cell and extracellular cell matrix (ECM) interactions provide cells with information essential for controlling morphogenesis, cell-fate specification, and cell death. In animals, one of the major groups of enzymes that degrade the ECM is the matrix metalloproteinases (MMPs). Here, we report the characterization of the cucumber (Cucumis sativus L. cv Marketmore) Cs1-MMP gene encoding such an enzyme likely to play a role in plant ECM degradation. Cs1-MMP has all the hallmark motif characteristics of animal MMPs and is a pre-pro-enzyme having a signal peptide, propeptide, and zinc-binding catalytic domains. Cs1-MMP also displays functional similarities with animal MMPs. For example, it has a collagenase-like activity that can cleave synthetic peptides and type-I collagen, a major component of animal ECM. Cs1-MMP activity is completely inhibited by a hydroxamate-based inhibitor that binds at the active site of MMPs in a stereospecific manner. The Cs1-MMP gene is expressed de novo at the end stage of developmental senescence, prior to the appearance of DNA laddering in cucumber cotyledons leaf discs and male flowers. As the steady-state level of Cs1-MMP mRNA peaks late in senescence and the pro-enzyme must undergo maturation and activation, the protease is probably not involved in nutrient remobilization during senescence but may have another function. The physiological substrates for Cs1-MMP remain to be determined, but the enzyme represents a good candidate for plant ECM degradation and may be involved in programmed cell death (PCD). Our results suggest that PCD occurs only at the culmination of the senescence program or that the processes are distinct with PCD being triggered at the end of senescence.

Studies on the subsite specificity of rat nardilysin (N-arginine dibasic convertase)

The subsite specificity of rat nardilysin was investigated using fluorogenic substrates of the type 2-aminobenzoyl-GGX(1)X(2)RKX(3)GQ-ethylenediamine-2,4- dinitrophenyl, where P(2), P(2)', and P(3) residues were varied. (The nomenclature of Schechter and Berger (Schechter, I., and Berger, A. (1967) Biochem. Biophys. Res. Commun. 27, 157-162) is used where cleavage of a peptide occurs between the P(1) and P(1)' residues, and adjacent residues are designated P(2), P(3), P(2)', P(3)', etc.) There was little effect on K(m) among different residues at any of these positions. In contrast, residues at each position affected k(cat), with P(2) residues having the greatest effect. The S(3), S(2), and S(2)' subsites differed in their amino acid preference. Tryptophan and serine, which produced poor substrates at the P(2) position, were among the best P(2)' residues. The specificity at P(3) was generally opposite that of P(2). Residues at P(2), and to a lesser extent at P(3), influenced the cleavage site. At the P(2) position, His, Phe, Tyr, Asn, or Trp produced cleavage at the amino side of the first basic residue. In contrast, a P(2) Ile or Val produced cleavage between the dibasic pair. Other residues produced intermediate effects. The pH dependence for substrate binding showed that the enzyme prefers to bind a protonated histidine. A comparison of the effect of arginine or lysine at the P(1)' or P(1) position showed that there is a tendency to cleave on the amino side of arginine and that this cleavage produces the highest k(cat) values.

Inhibition of alanyl-aminopeptidase suppresses the activation-dependent induction of glycogen synthase kinase-3beta (GSK-3beta) in human T cells

Inhibition of alanyl-aminopeptidase (APN, CD13) gene expression or enzymatic activity compromises T cell proliferation and function. Molecular mechanisms mediating these effects are not known as yet. Recently, we found the expression of the proto-oncogen Wnt-5a to be strongly affected by APN-inhibition. Wnt-5a and other members of the Wnt family of secreted factors are implicated in cell growth and differentiation. Here, we analyzed by quantitative RT-PCR and immunoblotting the expression in mitogen-activated T cells of a major constituent of the Wnt-5a pathway, glycogen synthase kinase-3beta (GSK-3beta). T cell activation by phytohaemagglutinin or pokeweed mitogen results in a strong increase of GSK-3beta mRNA amounts. At the protein level, we observed an up-regulation of both GSK-3beta and phosphorylated GSK-3beta. This induction-dependent increase of GSK-3beta is markedly reduced in response to inhibitors of alanyl-aminopeptidase, actinonin, leuhistin, and RB3014. These findings may provide a rational for the growth inhibition resulting from a diminished expression or activity of alanyl aminopeptidase.

Functional human insulin-degrading enzyme can be expressed in bacteria

Insulin-degrading enzyme (IDE) has been shown to degrade a number of biologically important peptides, including insulin and the amyloid-beta protein implicated in Alzheimer's disease. However, lack of a facile method to generate purified enzyme and related mutants has made it difficult to study the precise role of IDE in the clearance of these peptides. Therefore, we determined whether recombinant wild-type and mutant human IDEs can be overexpressed as functional enzymes in bacteria. Three vectors carrying cDNAs encoding N-terminally polyhistidine-tagged recombinant IDEs were constructed, and the proteins expressed in Escherichia coli were purified by metal affinity chromatography (final yield approximately 8 mg per liter of culture). The recombinant IDEs, like the endogenous mammalian enzyme, migrate with 110-kDa apparent molecular masses in SDS-polyacrylamide gels and as a approximately 200-kDa species in gel filtration. Further analysis by native PAGE indicates that IDE can form multimers of different complexities. The wild-type recombinant endopeptidase degrades insulin with an efficiency similar to that of the enzyme purified from mammalian tissues. Purified IDEs are stable at 4 degrees C for at least 1 month. Purified recombinant protein was used to raise specific polyclonal antibodies that can immunoprecipitate native mammalian IDE. Thus, the procedure described allows the rapid production of large amounts of purified IDE and demonstrates that IDE can be produced in an active form in the absence of other potential interacting mammalian proteins.

Analysis of the thyrotropin-releasing hormone-degrading ectoenzyme by site-directed mutagenesis of cysteine residues. Cys68 is involved in disulfide-linked dimerization

Thyrotropin-releasing hormone-degrading ectoenzyme is a member of the M1 family of Zn-dependent aminopeptidases and catalyzes the degradation of thyrotropin-releasing hormone (TRH; Glp-His-Pro-NH2). Cloning of the cDNA of this enzyme and biochemical studies revealed that the large extracellular domain of the enzyme with the catalytically active site contains nine cysteine residues that are highly conserved among species. To investigate the functional role of these cysteines in TRH-DE we used a site-directed mutagenesis approach and replaced individually each cysteine by a serine residue. The results revealed that the proteolytically truncated and enzymatically fully active enzyme consists of two identical subunits that are associated noncovalently by protein-protein interactions but not via interchain S-S bridges. The eight cysteines contained within this region are all important for the structure of the individual subunit and the enzymatic activity, which is dramatically reduced in all mutant enzymes. This is even true for the four cysteines that are clustered within the C-terminal domain remote from the Zn-binding consensus sequence HEICH. In contrast, Cys68, which resides within the stalk region seven residues from the end of the hydrophobic membrane-spanning domain, can be replaced by serine without a significant change in the enzymatic activity. Interestingly, this residue is involved in the formation of an interchain disulfide bridge. Covalent dimerization of the subunits, however, does not seem to be essential for efficient biosynthesis, enzymatic activity and trafficking to the cell surface.

Matrix metalloproteinase-2 contributes to ischemia-reperfusion injury in the heart

BACKGROUND

Matrix metalloproteinases (MMPs) contribute to collagen degradation and remodeling of the extracellular matrix after myocardial infarction; however, their role in myocardial dysfunction immediately after ischemia and reperfusion is unknown.

METHODS AND RESULTS

We measured the release of MMPs into the coronary effluent of isolated, perfused rat hearts during aerobic perfusion and reperfusion after ischemia. Aerobically perfused control hearts expressed pro-MMP-2 and MMP-2, as well as an unidentified 75-kDa gelatinase. These enzymes were also detected in the coronary effluent. After 20 minutes of global no-flow ischemia, there was a marked increase in pro-MMP-2 in the coronary effluent that peaked within the first minute of reperfusion. The release of pro-MMP-2 into the coronary effluent during reperfusion was enhanced with increasing duration of ischemia and correlated negatively with the recovery of mechanical function during reperfusion (r(2)=0.99). MMP-2 antibody (1.5 to 15 microg/mL) and the inhibitors of MMPs doxycycline (10 to 100 micromol/L) and o-phenanthroline (3 to 100 micromol/L) improved whereas MMP-2 worsened the recovery of mechanical function during reperfusion.

CONCLUSIONS

These results show that acute release of MMP-2 during reperfusion after ischemia contributes to cardiac mechanical dysfunction. The inhibition of MMPs may be a novel pharmacological strategy for the treatment of ischemia-reperfusion injury.

Molecular cloning and biochemical characterization of a new mouse testis soluble-zinc-metallopeptidase of the neprilysin family

Because of their roles in controlling the activity of several bio-active peptides, members of the neprilysin family of zinc metallopeptidases have been identified as putative targets for the design of therapeutic agents. Presently, six members have been reported, these are: neprilysin, endothelin-converting enzyme (ECE)-1 and ECE-2, the Kell blood group protein, PHEX (product of the phosphate-regulating gene with homologies to endopeptidase on the X chromosome) and X-converting enzyme (XCE). In order to identify new members of this important family of peptidases, we designed a reverse transcriptase-PCR strategy based on conserved amino acid sequences of neprilysin, ECE-1 and PHEX. We now report the cloning from mouse testis of a novel neprilysin-like peptidase that we called NL1. NL1 is a glycoprotein that, among the members of the family, shows the strongest sequence identity with neprilysin. However, in contrast with neprilysin and other members of the family which are type II integral membrane proteins, NL1 was secreted when expressed in cultured mammalian cells, likely due to cleavage by a subtilisin-like convertase at a furin-like site located 22 amino acid residues in the C-terminus of the transmembrane domain. The recombinant enzyme exhibited neprilysin-like peptidase activity and was efficiently inhibited by phosphoramidon and thiorphan, two inhibitors of neprilysin. Northern blot analysis and in situ hybridization showed that NL1 mRNA was found predominantly in testis, specifically in round and elongated spermatids. This distribution of NL1 mRNA suggests that it could be involved in sperm formation or other processes related to fertility.

Damage-induced neuronal endopeptidase (DINE) is a unique metallopeptidase expressed in response to neuronal damage and activates superoxide scavengers

We isolated a membrane-bound metallopeptidase, DINE (damage-induced neuronal endopeptidase), by differential display PCR using rat normal and axotomized hypoglossal nuclei. The most marked properties of DINE were neuron-specific expression and a striking response to axonal injury in both the central nervous system and peripheral nervous system. For instance, cranial and spinal nerve transection, ischemia, corpus callosum transection, and colchicine treatment increased DINE mRNA expression in the injured neurons, whereas kainate-induced hyperexcitation, immobilization, and osmotic stress failed to up-regulate DINE mRNA. Expression of DINE in COS cells partially inhibited C2-ceramide-induced apoptosis, probably because of the activation of antioxidant enzymes such as Cu/Zn-superoxide dismutase, Mn-superoxide dismutase, and glutathione peroxidase through the proteolytic activity of DINE. These data provide insight into the mechanism of how injured neurons protect themselves against neuronal death.

Aminopeptidase N/CD13 is directly linked to signal transduction pathways in monocytes

In the present study, we characterized in monocytes the rise in [Ca(2+)](i) evoked by monoclonal antibodies (mAbs) to aminopeptidase N (APN)/CD13, showing a two-phase calcium increase with a small-belled [Ca(2+)](i) rise due to the release of calcium from intracellular stores and a more sustained plateau due to the influx of calcium from the extracellular environment. Tyrosine kinase inhibitors were able to inhibit the rise in [Ca(2+)](i) induced by ligation APN/CD13, as were inhibitors of the phosphatidylinositol 3-kinase. For the first time we can show that mAbs to APN/CD13 provoke phosphorylation of the mitogen-activated protein kinases ERK1/2, JNK, and p38. Furthermore, we show that mRNA of the chemotactic cytokine IL-8 is upregulated under the influence of APN/CD13 ligation. Although the in vivo ligand as well as possible cooperating membrane molecules remains to be identified, our results suggest that the membrane ectoenzyme APN/CD13 is a novel signal transduction molecule in monocytes.