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PubMed2003

An aminopeptidase, ARTS-1, is required for interleukin-6 receptor shedding.

Aminopeptidase regulator of TNFR1 shedding (ARTS-1) binds to the type I tumor necrosis factor receptor (TNFR1) and promotes receptor shedding. Because hydroxamic acid-based metalloprotease inhibitors prevent shedding of both TNFR1 and the interleukin-6 receptor (IL-6Ralpha), we hypothesized that ARTS-1 might also regulate shedding of IL-6Ralpha, a member of the type I cytokine receptor superfamily that is structurally different from TNFR1. Reciprocal co-immunoprecipitation experiments identified that membrane-associated ARTS-1 directly binds to a 55-kDa IL-6Ralpha, a size consistent with soluble IL-6Ralpha generated by ectodomain cleavage of the membrane-bound receptor. Furthermore, ARTS-1 promoted IL-6Ralpha shedding, as demonstrated by a direct correlation between increased membrane-associated ARTS-1 protein, increased IL-6Ralpha shedding, and decreased membrane-associated IL-6Ralpha in cell lines overexpressing ARTS-1. The absence of basal IL-6Ralpha shedding from arts-1 knock-out cells identified that ARTS-1 was required for constitutive IL-6Ralpha shedding. Furthermore, the mechanism of constitutive IL-6Ralpha shedding requires ARTS-1 catalytic activity. Thus, ARTS-1 promotes the shedding of two cytokine receptor superfamilies, the type I cytokine receptor superfamily (IL-6Ralpha) and the TNF receptor superfamily (TNFR1). We propose that ARTS-1 is a multifunctional aminopeptidase that may modulate inflammatory events by promoting IL-6Ralpha and TNFR1 shedding.

Aminopeptidases↗
PubMed2006

Enzymatic properties of human aminopeptidase A. Regulation of its enzymatic activity by calcium and angiotensin IV.

Aminopeptidase A (APA) is a type II membrane-bound protein implicated in the regulation of blood pressure in the brain renin-angiotensin system. In this study, a recombinant soluble form of APA was expressed in a baculovirus system, purified to homogeneity, and characterized. By using synthetic substrates, it was shown that although the enzyme has a rather broad substrate specificity in the absence of Ca2+, the preferential release of acidic amino acid residues was observed in the presence of Ca2+. Moreover, Ca2+ up- or down-regulated the enzymatic activity depending on the substrate. By searching for natural substrates of APA, we found that peptides having acidic amino acids at their N terminus (angiotensin II, neurokinin B, cholecystokinin-8, and chromogranin A) were cleaved by the enzyme efficiently in the presence but not in the absence of Ca2+. Moreover kallidin (Lys-bradykinin) was converted to bradykinin effectively only in the absence of Ca2+. These results suggest that Ca2+ increases the preference of the enzyme for the peptide substrates having N-terminal acidic amino acids. In addition, we found that angiotensin IV could bind to APA both in the presence and absence of Ca2+ and inhibited the enzymatic activity of APA competitively, suggesting that angiotensin IV acts as a negative regulator of the enzyme once generated from angiotensin II by the serial actions of aminopeptidases. Taken together, these results suggest that there exists a complex regulation of the enzymatic activity of APA, which may contribute to homeostasis such as regulation of blood pressure, maintenance of memory, and normal pregnancy by controlling the concentrations of peptide substrates.

Amino Acid Sequence↗
PubMed2006

Characterization of the Plasmodium falciparum M17 leucyl aminopeptidase. A protease involved in amino acid regulation with potential for antimalarial drug development.

Amino acids generated from the catabolism of hemoglobin by intra-erythrocytic malaria parasites are not only essential for protein synthesis but also function in maintaining an osmotically stable environment, and creating a gradient by which amino acids that are rare or not present in hemoglobin are drawn into the parasite from host serum. We have proposed that a Plasmodium falciparum M17 leucyl aminopeptidase (PfLAP) generates and regulates the internal pool of free amino acids and therefore represents a target for novel antimalarial drugs. This enzyme has been expressed in insect cells as a functional 320-kDa homo-hexamer that is optimally active at neutral or alkaline pH, is dependent on metal ions for activity, and exhibits a substrate preference for N-terminally exposed hydrophobic amino acids, particularly leucine. PfLAP is produced by all stages in the intra-erythrocytic developmental cycle of malaria but was most highly expressed by trophozoites, a stage at which hemoglobin degradation and parasite protein synthesis are elevated. The enzyme was located by immunohistochemical methods and by transfecting malaria cells with a PfLAP-green fluorescent protein construct, to the cytosolic compartment of the cell at all developmental stages, including segregated merozoites. Amino acid dipeptide analogs, such as bestatin and its derivatives, are potent inhibitors of the protease and also block the growth of P. falciparum malaria parasites in culture. This study provides a biochemical basis for the antimalarial activity of aminopeptidase inhibitors. Availability of functionally active recombinant PfLAP, coupled with a simple enzymatic readout, will aid medicinal chemistry and/or high throughput approaches for the future design/discovery of new antimalarial drugs.

Amino Acids↗
PubMed1990

Aminopeptidase N is directly sorted to the apical domain in MDCK cells.

In different epithelial cell types, integral membrane proteins appear to follow different sorting pathways to the apical surface. In hepatocytes, several apical proteins were shown to be transported there indirectly via the basolateral membrane, whereas in MDCK cells a direct sorting pathway from the trans-Golgi-network to the apical membrane has been demonstrated. However, different proteins had been studied in these cells. To compare the sorting of a single protein in both systems, we have expressed aminopeptidase N, which already had been shown to be sorted indirectly in hepatocytes, in transfected MDCK cells. As expected, it was predominantly localized to the apical domain of the plasma membrane. By monitoring the appearance of newly synthesized aminopeptidase N at the apical and basolateral surface, it was found to be directly sorted to the apical domain in MDCK cells, indicating that the sorting pathways are indeed cell type-specific.

Aminopeptidases↗
PubMed1996

Identification of a cytoplasm to vacuole targeting determinant in aminopeptidase I.

Aminopeptidase I (API) is a soluble leucine aminopeptidase resident in the yeast vacuole (Frey, J., and K.H. Rohm. 1978. Biochim. Biophys. Acta. 527:31-41). The precursor form of API contains an amino-terminal 45-amino acid propeptide, which is removed by proteinase B (PrB) upon entry into the vacuole. The propeptide of API lacks a consensus signal sequence and it has been demonstrated that vacuolar localization of API is independent of the secretory pathway (Klionsky, D.J., R. Cueva, and D.S. Yaver. 1992. J. Cell Biol. 119:287-299). The predicted secondary structure for the API propeptide is composed of an amphipathic alpha-helix followed by a beta-turn and another alpha-helix, forming a helix-turn-helix structure. With the use of mutational analysis, we determined that the API propeptide is essential for proper transport into the vacuole. Deletion of the entire propeptide from the API molecule resulted in accumulation of a mature-sized protein in the cytosol. A more detailed examination using random mutagenesis and a series of smaller deletions throughout the propeptide revealed that API localization is severely affected by alterations within the predicted first alpha-helix. In vitro studies indicate that mutations in this predicted helix prevent productive binding interactions from taking place. In contrast, vacuolar import is relatively insensitive to alterations in the second predicted helix of the propeptide. Examination of API folding revealed that mutations that affect entry into the vacuole did not affect the structure of API. These data indicate that the API propeptide serves as a vacuolar targeting determinant at a critical step along the cytoplasm to vacuole targeting pathway.

Amino Acid Sequence↗
PubMed2002

Tetrahedral aminopeptidase: a novel large protease complex from archaea.

A dodecameric protease complex with a tetrahedral shape (TET) was isolated from Haloarcula marismortui, a salt-loving archaeon. The 42 kDa monomers in the complex are homologous to metal-binding, bacterial aminopeptidases. TET has a broad aminopeptidase activity and can process peptides of up to 30-35 amino acids in length. TET has a central cavity that is accessible through four narrow channels (<17 A wide) and through four wider channels (21 A wide). This architecture is different from that of all the proteolytic complexes described to date that are made up by rings or barrels with a single central channel and only two openings.

Amino Acid Sequence↗
PubMed1996

An aminopeptidase inhibitor, bestatin, enhances gonadotrophin-stimulated ovulation in mice.

The role of aminopeptidases in follicular growth and/or ovulation in vivo was examined. We injected an inhibitor of cell-surface aminopeptidases, bestatin (4 mg/ml, 100 microliters), i.p. four times during 2 days into 20 day old female ICR mice, in which follicular growth and ovulation were stimulated by pregnant mare's serum gonadotrophin (PMSG, 5 IU) and human chorionic gonadotrophin (HCG, 5 IU). The number of ovulated oocytes was estimated by counting the number of oocytes in the oviduct 19 h after HCG injection. The mean +/- SD number of ovulated oocytes in bestatin-treated mice was significantly higher than that in control mice [47.00 +/- 18.13 (n = 26) versus 35.90 +/- 10.14 (n = 28), P < 0.01]. To confirm the direct effect of bestatin on the ovary, bestatin (2 mg/ml, 3 microliters) or its stereoisomer (2 mg/ml, 3 microliters) with very weak inhibitory activity was unilaterally injected into the ovarian bursa 24 h before the administration of PMSG. As a control, buffer (3 microliters) was injected into the contralateral bursa. In some experiments, bestatin (2 mg/ml, 3 microliters) was injected just before HCG administration. The administration of bestatin via the ovarian bursa prior to PMSG administration significantly increased the number of ovulated oocytes per oviduct from the treated compared with the contralateral ovary [23.70 +/- 9.61 versus 17.10 +/- 5.83 (n = 25), P < 0.01], whereas its stereoisomer elicited no significant effects. The administration of bestatin just before HCG administration also had no effect. These findings indicate that membrane-bound peptidase(s) present on murine ovarian cells is an important regulating factor(s) of follicular growth and/or ovulation.

Aminopeptidases↗
PubMed1990

Purification and characterization of an aminopeptidase from sperm of the sea urchin, Strongylocentrotus intermedius. Ca2(+)-dependent substrate specificity as a novel feature of the enzyme.

An aminopeptidase showing broad substrate specificity was purified to electrophoretic homogeneity from spermatozoa of the sea urchin, Strongylocentrotus intermedius. It is a single chain protein (Mr = 110,000) with an isoelectric point of 5.2 and shows the highest activity in a pH range between 7.0 and 7.5. Ni2+, Cu2+, Zn2+, and Hg2+, as well as 1,10-phenanthroline and p-chloromercuribenzoate, inhibit the enzyme irrespective of the substrates used, but Ca2+, Mn2+, Mg2+, and Co2+ modified the activity differently depending on the nature of the substrate. The effect of Ca2+ was most marked; it stimulated the activity toward some 4-methylcoumaryl-7-amide (MCA) substrates (for example leucine MCA), whereas it depressed the activity toward some other substrates such as arginine-MCA and lysine-MCA in a competitive manner. The rate of enzymatic hydrolysis determined for a mixture of leucine-MCA and arginine-MCA, in respect to the release of their common product (7-amino-4-methylcoumarin), was in good agreement with the value calculated on the assumption that these two substrates compete with each other for a single active site of the enzyme. Furthermore, the enzyme showed an identical Ki value for each of the competitive inhibitors examined, irrespective of the type of substrate. Ca2+ also influenced the activities toward various peptide substrates in a dual way similar to that observed on the MCA substrates. These results indicate that the sea urchin sperm aminopeptidase has an active site that alters its substrate preference depending on the Ca2+ concentration of the reaction medium.

Aminopeptidases↗
PubMed1980

Porcine liver aminopeptidase B. Substrate specificity and inhibition by amino acids.

Porcine liver aminopeptidase B[EC 3.4.11.6] is highly specific for hydrolysis of beta-naphthylamides of basic L-amino acids; the Km values for L-arginine beta-naphthylamide and L-lysine beta-naphthylamide were 0.035 and 0.12 mM, respectively. The enzyme was inhibited by various alpha-amino acids. Among basic amino acids, L-homoarginine and L-arginine were the most potent inhibitors, L-lysine and L-norarginine (alpha-amino-gamma-guanidinobutyric acid) being less inhibitory. Hydrophobic amino acids also inhibited the enzyme competitively. This suggests that there is a hydrophobic region that binds the side chain of the substrates or inhibitors in the specificity site of the enzyme. Studies on the inhibitions by L-arginine derivatives showed that blocking of the alpha-carboxyl or the alpha-amino group reduced the inhibitory effect of L-arginine. Porcine liver aminopeptidase B was not inhibited by puromycin, whereas bestatin inhibited the enzyme competitively with a Ki value of 1.4 X 10(-8) M. This enzyme had no kinin-converting activity.

Amino Acids↗
PubMed1984

Purification and characterization of an aminopeptidase from bovine leukocytes.

An aminopeptidase was purified about 4,000-fold from the clarified homogenate of bovine leukocytes by a series of column chromatographies on DEAE-cellulose, hydroxyapatite, Sephadex G-150, and DEAE-Toyopearl. The purified enzyme had a specific activity of 3.8 mumol X min-1 X mg-1 with arginine beta-naphthylamide (Arg-2-NNap) as substrate, and a minute amount of contaminating protein was found to be present by gel electrophoresis. The molecular weight of the enzyme was estimated to be 94,000 by gel filtration on Sephadex G-150. The enzyme had a broad substrate specificity and a pH optimum between 6.5 and 7.0 for the hydrolysis of alpha-aminoacyl beta-naphthylamides. It hydrolyzed beta-naphthylamides of basic, aliphatic, and aromatic amino acids, and also catalyzed the liberation of amino-terminal phenylalanine from phenylalanyl peptides. The enzyme was inhibited by bestatin, puromycin, 1,10-phenanthroline, sulfhydryl reagents, and a variety of heavy metal ions. Only the cobaltous ion stimulated the enzyme and the values of both Km and Vmax for Arg-2-NNap increased. In gross properties the present enzyme resembles porcine liver aminopeptidase reported previously (Kawata, S., et al. (1982) J. Biochem. 92, 1093-1101) very closely.

Aminopeptidases↗
PubMed1999

Deletion of the four C-terminal residues of PepC converts an aminopeptidase into an oligopeptidase.

The aminopeptidase PepC is a cysteine peptidase isolated from lactic acid bacteria. Its structural and enzymatic properties closely resembles those of the bleomycin hydrolases, a group of cytoplasmic enzymes isolated from eukaryotes. Previous biochemical and structural data have shown that the C-terminal end of PepC partially occupies the active site cleft. In this work the substrate specificity of PepC was engineered by deletion of the four C-terminal residues. The mutant PepCDelta432-435 cleaved peptide substrates as an oligopeptidase while the aminopeptidase specificity was totally abolished. The substrate size dependency indicated that PepCDelta432-435 possesses an extended binding site able to accommodate four residues of the substrate on both sides of the cleaved bond. The activity of PepCDelta432-435 towards tryptic fragments of casein revealed a preference for peptides with hydrophobic amino acids at positions P2 and P3 and for Gly, Asn and Gln at position P1. PepCDelta432-435 was shown to be highly sensitive to the thiol peptidase inhibitors leupeptin or E64 which are inefficient towards the wild-type PepC. In conclusion, deletion of the four C-terminal residues in PepC produces a new enzyme with properties resembling those of an endopeptidase from the papain family.

Aminopeptidases↗
PubMed2001

The induction of tomato leucine aminopeptidase genes (LapA) after Pseudomonas syringae pv. tomato infection is primarily a wound response triggered by coronatine.

Tomato plants constitutively express a neutral leucine aminopeptidase (LAP-N) and an acidic LAP (LAP-A) during floral development and in leaves in response to insect infestation, wounding, and Pseudomonas syringae pv. tomato infection. To assess the physiological roles of LAP-A, a LapA-antisense construct (35S:asLapA1) was introduced into tomato. The 35S:asLapA1 plants had greatly reduced or showed undetectable levels of LAP-A and LAP-N proteins in healthy and wounded leaves and during floral development. Despite the loss of these aminopeptidases, no global changes in protein profiles were noted. The 35S:asLapA1 plants also exhibited no significant alteration in floral development and did not impact the growth and development of Manduca sexta and P. syringae pv. tomato growth rates during compatible or incompatible infections. To investigate the mechanism underlying the strong induction of LapA upon P. syringae pv. tomato infection, LapA expression was monitored after infection with coronatine-producing and -deficient P. syringae pv. tomato strains. LapA RNA and activity were detected only with the coronatine-producing P. syringae pv. tomato strain. Coronatine treatment of excised shoots caused increases in RNAs for jasmonic acid (JA)-regulated wound-response genes (LapA and pin2) but did not influence expression of a JA-regulated pathogenesis-related protein gene (PR-1). These results indicated that coronatine mimicked the wound response but was insufficient to activate JA-regulated PR genes.

Amino Acids↗
PubMed2003

Lymphatic microvessels in the rat remnant kidney model of renal fibrosis: aminopeptidase p and podoplanin are discriminatory markers for endothelial cells of blood and lymphatic vessels.

ABSTRACT. Rat remnant kidney is an established model of renal tubulointerstitial fibrosis and progression to end-stage renal failure. The morphologic lesions comprise nephron loss and regeneratory tubular hypertrophy, interstitial infiltration, predominately by macrophages, and progressive fibrosis. A critical role in this complex pathology was assigned to tubulointerstitial blood microvessels that regulate the supply of oxygen and nutrients of tubuli. Whereas some investigations reported a rarefaction of the vascular network in association with the degenerative cortical changes, others observed an increase in vascularization. Here these discrepant findings are addressed by reinvestigation of the vascularization of rat remnant kidneys by the use of two novel endothelial lineage specific, discriminatory markers, i.e., the membrane mucoprotein podoplanin with specificity for lymphatic endothelia, and the glycosyl-phosphatidylinositol (GPI)-anchored membrane enzyme aminopeptidase P that is recognized by a monoclonal antibody designated JG12 and that is specifically expressed by endothelial cells of blood vessels only. The results obtained confirm a regional rarefaction of aminopeptidase P-positive blood microvessels; they also establish major changes in the renal lymphatic vasculature. Massive proliferation of lymphatic vessels was observed in fibrotic tubulointerstitial regions, whereas in kidneys of sham-operated rats, only a few lymphatic vessels were found adjoined with arteries. The lymphatic vessels frequently contained mononuclear cells that were also encountered in the interstitial spaces and expressed relative large amounts of vascular endothelial growth factor-C mRNA by in situ hybridization. Collectively, these results indicate that a large proportion of the microvessels encountered in the cortex of remnant kidneys are of lymphatic origin and cannot be discriminated by common endothelial markers, such as CD34, that are expressed by both lymphatic and blood endothelia cells. As lymphatic endothelial cells secrete chemokines that attract dendritic cells, it is possible that the increase in lymphatic vascularization could enhance the immunologic surveillance of remnant kidneys.

Aminopeptidases↗
PubMed2005

The leucyl aminopeptidase from Helicobacter pylori is an allosteric enzyme.

This study describes the cloning, genetic analysis and biochemical characterization of a leucyl aminopeptidase (LAP) from Helicobacter pylori. A gene encoding LAP was cloned from H. pylori and the expressed 55 kDa protein displayed homology to aminopeptidases from Gram-negative bacteria, plants and mammals. This LAP demonstrated amidolytic activity against L-leucine-p-nitroanilide. Optimal activity was observed at pH 8.0 and 45 degrees C, with V(max) of 232 mumol min(-1) (mg protein)(-1) and S(0.5) of 0.65 mM. The data suggest that LAP could be allosteric (n(H)=2.27), with regulatory homohexamers, and its activity was inhibited by ion chelators and enhanced by divalent manganese, cobalt and nickel cations. Bestatin inhibited both LAP activity (IC(50)=49.9 nM) and H. pylori growth in vitro. The results point to the potential use of LAP as a drug target to develop novel anti-H. pylori agents.

Allosteric Regulation↗
PubMed2004

Preliminary crystallographic characterization of BSAP, an extracellular aminopeptidase from Bacillus subtilis.

The extracellular aminopeptidase from Bacillus subtilis (BSAP) has recently been cloned, overexpressed and purified from Escherichia coli. It is a monomer with a molecular weight of 46 425 Da, consisting of 425 amino-acid residues and a double-zinc catalytic centre. The recombinant enzyme was found to be stable for 20 min at 353 K, to function optimally in the pH range 8-9 and to prefer basic and large hydrophobic N-terminal amino acids in peptide and protein substrates. As such, this enzyme can be used as a representative model for structural, functional and mechanistic studies of monomeric double-zinc aminopeptidases, many of which have been found to be involved in medically important biological activities. In this report, the crystallization and preliminary crystallographic characterization of wild-type BSAP are described. Two different crystal forms are reported, of which the hexagonal form H2 is the more suitable for structural study, with average unit-cell dimensions a = b = 226.5, c = 42.8 A. A full diffraction data set has been collected from such a crystal of the native enzyme (2.2 A resolution, 91.2% completeness, R(merge) = 7.1%). A multiwavelength anomalous diffraction (MAD) data set was collected on native (zinc-containing) BSAP at three wavelengths around the zinc absorption edge (peak data set at 2.5 A resolution, 98.8% completeness, R(merge) = 5.3%). These diffraction data were collected at 95-100 K using a synchrotron X-ray source and a CCD area detector. The data are currently being used to obtain crystallographic phasing and to determine the detailed three-dimensional structure of the enzyme.

Aminopeptidases↗
PubMed2005

Expression, purification, crystallization and preliminary crystallographic analysis of a deblocking aminopeptidase from Pyrococcus horikoshii.

The deblocking aminopeptidase (DAP) of Pyrococcus horikoshii is a hyperthermophilic exoprotease that cleaves the N-terminal amino acid of peptide substrates with a putative deblocking activity for acylated peptides. DAP has been found to be homologous to a tetrahedral aminopeptidase from the halophilic Haloarcula marismortui. The latter enzyme is a dodecameric complex and has been revealed to be a self-compartmentalized protease whose central cavity harbouring the catalytic site is accessible through several channels of different size, unlike all other known proteolytic complexes. Three paralogues of DAP have been identified in P. horikoshii, with about 40% identity between them. Each of them has been overexpressed in Escherichia coli, purified and crystallized in the native and selenomethionine-substituted states. The results indicate that they form two kinds of assemblies, of 12 and of 24 subunits, with a molecular weight of approximately 400 and approximately 800 kDa, respectively. Crystals of the different variants of DAP and in their different oligomeric states diffract up to a resolution of 3 A.

Aminopeptidases↗
PubMed1982

Electrophoretic types of leucine aminopeptidase in sheep serum.

Leucine aminopeptidase in sheep serum was studied by starch gel electrophoresis. Two phenotypes, A and B, were observed, of which the former was present in 70-90% of all the sheep examined. These two phenotypes have been shown to be controlled by a single autosomal locus, with two alleles LapA and LapB. The LapA allele is dominant. The frequencies of Lap phenotypes and alleles were determined in eleven Spanish and two foreign breeds. Serum alkaline phosphatase and serum leucine aminopeptidase are electrophoretically distinct.

Alkaline Phosphatase↗