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At least 775 records · Page 43Linked to original sources
PubMed1986

Determination of the signal peptidase cleavage site in the preprosubtilisin of Bacillus subtilis.

Bacillus subtilis subtilisin is predicted to be synthesized as a preproenzyme according to the sequence analysis of its gene. We have synthesized the [35S] methionine-labeled preprosubtilisin in vitro and processed the precursor to prosubtilisin by the addition of membrane vesicles derived from vegetative cells of B. subtilis and Triton X-100. Radiosequencing of the prosubtilisin allowed the precise determination of the signal peptidase cleavage site. The preprosubtilisin was found to have a 29-amino-acid-long signal peptide with the signal peptidase cleavage sequence of AlaGln-AlaAla. Fusion of the signal peptide sequence to the mature TEM beta-lactamase structural gene allowed the production of an active and secreted form of beta-lactamase in vivo. An N-terminal sequence analysis of this product indicated that the observed in vivo signal peptidase cleavage site was exactly the same as that determined by in vitro analysis. During the development of the in vitro processing system, we demonstrated that the replacement of the subtilisin transcription regulatory sequence by a vegetative promoter allowed the vegetative expression and secretion of subtilisin. Thus, the late expression of the native subtilisin gene is mainly controlled at the transcription level and the secretion/processing systems are available for vegetative production of subtilisin.

Amino Acid Sequence↗
PubMed1988

Characterization of the internal signal-anchor domain of Escherichia coli leader peptidase.

Leader peptidase, an integral transmembrane protein of Escherichia coli, is synthesized without a cleavable amino-terminal leader peptide. Of the five domains that participate in the membrane assembly of this protein, one is an internal "signal" region. We have used oligonucleotide-directed mutagenesis to examine the properties of the internal signal that are crucial for leader peptidase assembly. For this purpose, the net charge at the amino terminus of the internal signal was changed from +2 to +1 and -1 and, at the carboxyl terminus of the signal, from 0 to -1 or +1. These mutations had no effect on the membrane assembly of leader peptidase, suggesting that the charges have little role in the signal function. The apolar core of this signal was disrupted by substitution of basic amino acids for apolar residues. Substitution of an arginyl residue at position 70, or two arginyl residues at position 67 and 69, prevented membrane assembly. However, substitution of an arginyl residue at position 66 or either arginyl or lysyl residue at position 68 was without effect. Thus, while the apolar character of the internal signal is important, the precise position of a charged residue determines its effect on assembly.

Endopeptidases↗
PubMed1988

Substrate specificity of eukaryotic signal peptidase. Site-saturation mutagenesis at position -1 regulates cleavage between multiple sites in human pre (delta pro) apolipoprotein A-II.

We have previously described a novel mutant of human preproapolipoprotein A-II (pre(delta pro)apoA-II) in which the wild-type 18-amino acid-long signal sequence (Gly18 decreases) was functionally redefined to 20 amino acids in length (Ala 20 decreases). We have used this mutant as a model preprotein to probe the substrate specificity of eukaryotic signal peptidase. Site-saturation mutagenesis was performed resulting in the substitution of 13 different amino acids (acidic, basic, aromatic, hydrophobic, and small-neutral) for Ala20 (or position -1). The effects of these substitutions were assessed using an in vitro transcription/translation/microsomal membrane processing system. NH2-terminal sequence analysis of the 13 mutant proteins demonstrated that amino acids which occupy position -1 in a signal peptide are critical in establishing a good context for signal peptidase cleavage and that two or more potential sites of cleavage may compete for recognition by signal peptidase.

Amino Acid Sequence↗
PubMed1987

The effects of deleting the propeptide from human preproapolipoprotein A-I on co-translational translocation and signal peptidase processing.

The two principal protein components of human high density lipoprotein particles, apoA-I and apoA-II, are initially synthesized as prepropolypeptides. The function of their NH2-terminal prosegments is not known. We have previously shown that deletion of the pentapeptide prosegment (Ala-Leu-Val-Arg-Arg) from human preproapoA-II redirects signal peptidase cleavage to a site located between the second and third residues of the mature protein (Folz, R. J., and Gordon, J. I. (1986) J. Biol. Chem. 261, 14752-14759). The hexapeptide prosegment of human preproapoA-I differs from other NH2-terminal propeptides in that it terminates with paired glutamine residues (Arg-His-Phe-Trp-Gln-Gln). To examine its role in the early events of protein export, we isolated a full-length human preproapoA-I cDNA and deleted its propeptide coding region by oligonucleotide-directed mutagenesis. The effects of this deletion on co-translational translocation and signal peptidase processing were assessed using an in vitro transcription/translation/microsomal membrane processing system. Propeptide deletion reduces the efficiency of co-translational translocation/processing in both reticulocyte and wheat germ lysates but does not affect the fidelity of signal peptidase cleavage. This reduced efficiency does not appear to reflect differences in signal recognition particle-nascent protein interaction as measured by a translational arrest assay. However, differences in translocation/processing rates were noted in a postinitiation translocation/cleavage assay. This assay employed the initiation inhibitor edeine to generate nascent wild type and mutant proteins of increasing chain length which were subsequently presented to canine pancreatic membranes. Unlike preproapoA-I, pre(delta pro)apoA-I retained its ability to undergo translocation and proteolytic processing even after the entire protein was synthesized. These data suggest that the propeptide in human preproapoA-I may play a role in promoting an optimal structure for co-translational translocation and processing.

Amino Acid Sequence↗
PubMed1987

[p-Nitroanilides of amino acids and peptides and fluorescence peptide with inner fluorescence quenching as substrates for cathepsins H, B, D and high molecular weight aspartic peptidase in the brain].

p-Nitroanilides of amino acids and peptides were used to study the specificity of cathepsins H and B from human and bovine brain, respectively. The specific activity of cathepsin H decreased in the following order: Arg-pNa greater than or equal to Leu-pNa greater than Ala-pNa greater than or equal to Phe-pNa greater than Pro-pNa greater than Glu-pNa; Arg-pNa was split by the enzyme 12 times as fast as Bz-Arg-pNa. Among other oligopeptide p-nitroanilides tested (Ala-Ala, Ala-Leu, Ala-Ala-Ala, Ala-Ala-Leu, Gly-Gly-Leu, Gly-Gly-Phe, Gly-Leu-Phe, pGlu-Phe-Leu, pGlu-Phe-Ala, pGlu-Phe), PGlu-Phe-Leu and pGlu-Phe-Ala appeared to be the best substrates for cathepsin B; Km for hydrolysis were 0.1 mM and 0.165 mM, respectively, kcat were 5.1 and 8.3 s-1, respectively. A comparative study of substrate specificity of cathepsin D and high molecular weight aspartic peptidase with the use of fluorescent substrate with inner fluorescence quenching, Abz-Ala-Ala-Phe-Phe-pNa, revealed that both peptidases hydrolyzed the single bond between two phenylalanine residues, resulting in the increase of fluorescence (4.5-5-fold) of anthraniloyl tripeptide. The Km values for the substrate hydrolysis by cathepsin D and high molecular weight aspartic peptidase were 6.2 microM and 11.2 microM; kcat were 7.2 s-1 and 1.3 s-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1986

The cystatins: a diverse superfamily of cysteine peptidase inhibitors.

The cystatins comprise a homologous group of protein inhibitors of peptidases, of which the first to be studied in detail was chicken cystatin from egg-white. Three distinct protein families or "types" are recognized within the cystatin superfamily. The type 1 cystatins (also called "stefins") are the simplest in structure, being single chains of about 100 amino acids, with no disulphide bonds or carbohydrate. The Type 2 cystatins, which include the egg-white protein, have about 115 amino acids, and two disulphide loops, but still no carbohydrate. The Type 3 cystatins are the plasma kininogens in which each molecule contains three divergent copies of the typical cystatin sequence differing in activity as well as structure; these complex inhibitor molecules contain disulphide bonds and also carbohydrate groups. The cystatins inhibit most cysteine endopeptidases of the papain type, and also the exopeptidase dipeptidyl peptidase I. Each cystatin molecule has a single reactive site for all the peptidases it inhibits, but there are large differences in K(i) values for different combinations of cystatin and enzyme, and calpains are inhibited only by one of the segments of the kininogens. The cystatins have many important characteristics in common, but their differences in molecular structure imply different routes of biosynthesis, are associated with different in vivo distributions, and suggest a variety of physiological functions.

Animals↗
PubMed1987

Potentiation of enkephalin action by peptidase inhibitors in rat locus ceruleus in vitro.

Intracellular recordings were made from locus ceruleus (LC) neurons in slices of rat pons. It has been shown previously that opioids inhibit firing and hyperpolarize LC neurons by activating mu-opioid receptors. Concentration-response curves were constructed by measuring the hyperpolarization, or outward current at -60 mV, caused by various opioid agonists added to the superfusing solution. Peptidase inhibitors (kelatorphan, bestatin and thiorphan) each increased the potency of Met-enkephalin, Leu-enkephalin and metorphamide but had no effect of their own on the LC neurons. Kelatorphan (20 microM) produced a 7-fold shift to the left of the Met-enkephalin dose-response curve. Higher concentrations produced no further shift. Thiorphan (3 microM) and bestatin (20 microM) each had a smaller potentiating effect on the Met-enkephalin hyperpolarization. The effects of Tyr-D-Ala-Gly-MePhe-Gly-ol and noradrenaline were not potentiated by these peptidase inhibitors. Electrical stimulation produced an inhibitory synaptic potential that was prolonged by cocaine (10 microM) and blocked by the alpha-2 adrenoceptor antagonist idazoxan (1 microM). After addition of idazoxan, hyperpolarizing synaptic potentials could be evoked even in the presence of kelatorphan (20 microM). These results indicate that peptide metabolism in the intact brain slice can account for a substantial decrease in the sensitivity of LC neurons to exogenously applied opioid peptides; even after peptidase inhibition, no evidence could be obtained for hyperpolarizing synaptic potentials due to the release of endogenous opioids.

Analgesics↗
PubMed1979

[Substrate specificity of peptidases catalyzing LH-RH degradation in hypothalamus, liver and heart of rat].

Degradation of [125I]-LH-RH by peptidases of hypothalamus, liver and heart of the rat and the effects of LH-RH, LH-RH antagonist D-Phe2-Phe3-D-Phe6-LH-RH, LH-RH5-10, oxytocin, bradikinin, thyrotrophin-releasing hormone, melanocyte-inhibiting factor, luteinizing, follicle-stimulating, lactogenic and growth hormones were studied. It was shown that the degradation was inhibited with maximal efficiency by non-labelled LH-RH (Ki = 1,7--2,0 . 10(-6) M). This observation is indicative of peptidase specificity for LH-RH. It is assumed that specific peptidases of liver and heart are involved in the reglation of LH-RH concentration in these organs.

Animals↗
PubMed1985

Conserved residues of the leader peptide are essential for cleavage by leader peptidase.

Gene 8 of bacteriophage M13 codes for procoat, the precursor of its major coat protein. Gene 8 has been cloned into a plasmid and mutagenized. We have isolated mutants of this gene in which procoat is synthesized but is not processed to coat protein. We now describe mutants in the leader region of procoat, at positions -6, -3, and -1 with respect to the leader peptidase cleavage site. These positions are quite conserved among the leader peptides of various pre-proteins. Each of these mutant procoats is synthesized at a normal rate and inserts correctly into the plasma membrane, as judged by its accessibility to protease in intact spheroplasts. Procoat accumulates, largely in its transmembrane form, and is not cleaved to coat. In detergent extracts, the mutant procoats are very poor substrates for added leader peptidase. We conclude that these 3 residues are not conserved for insertion across the membrane but are part of an essential recognition site for the leader peptidase.

Bacteriophages↗
PubMed1977

Peptidases of the kidney microvillus membrane.

The microvillus membrane of the kidney is highly differentiated in its complement of enzymes and other proteins. In addition to the five well documented peptidases that are present in the membrane, recent work suggests that aminopeptidase P, carboxypeptidase P and an enzyme tentatively referred to as "leucine hydrazidase" are also microvillus enzymes. Microvillus serine peptidase (dipeptidyl peptidase IV) has been purified after detergent solubilization. The catalytic and molecular properties of this form and the form released by autolysis have been compared in an attempt to gain understanding of the intramembranous domain of this protein. Current views on the molecular organization of the microvillus are discussed.

Animals↗
PubMed1983

Thiol-protein disulfide oxidoreductase and peptidase activities in insulinoma tissue.

An islet cell tumor, characterized by proinsulin level significantly elevated above normal human pancreas, has been found to contain insulin- and glucagon-degrading activity. Examination by chromatography on Sephadex G-75 of the degradation products formed from insulin showed A chain, and B chain rich-A chain aggregate as previously found with rat pancreatic islets. There was, however, little conversion of A chain to low molecular weight components indicating that insulinoma peptidase that has been found to degrade glucagon at about pH 6.8 degraded that A chain to a markedly lower rate. In contrast to the insulin-degrading activity, which was activated by glutathione in the presence of EDTA, the peptidase activity was not affected by the thiol compound. The activity of the peptidase was markedly inhibited by chelating agents, i.e., EDTA and o-phenanthroline, whereas chymotrypsin and trypsin inhibitors, i.e., TOS-PheCH2Cl, TOS-LysCH2Cl, soybean and pancreas trypsin inhibitor were found to have no effect.

Adenoma, Islet Cell↗
PubMed1983

Hen oviduct signal peptidase is an integral membrane protein.

Membrane preparations from rough endoplasmic reticulum of hen oviduct resemble those of dog pancreas in their capacity to translocate nascent secretory proteins into membrane vesicles present during cell-free protein synthesis. As with the dog membranes, the precursor form of human placental lactogen is transported into the vesicles and processed to the native secretory form by an associated "signal peptidase." The oviduct microsomal membranes glycosylate nascent ovomucoid and ovalbumin in vitro. Attempts to extract the signal peptidase from these membrane vesicles revealed that it is one of the least easily solubilized proteins. A protocol for enrichment of signal peptidase was developed that took advantage of its tight association with these vesicles. These studies indicate that the enzyme has the characteristics of an integral membrane protein which remains active in membrane vesicles even after extraction with low concentrations of detergent that do not dissolve the lipid bilayer or after disruption of membrane vesicles in ice-cold 0.1 M Na2CO3, pH 11.5 (Fujiki, Y., Hubbard, A. L., Fowler, S., and Lazarow, P.B. (1982) J. Cell Biol. 93, 97-102), which releases the majority of membrane-associated proteins. Solubilization requires concentrations of nondenaturing detergents that totally dissolve the lipid bilayer. The detergent-solubilized enzyme retains the activity and the characteristic specificity of the membrane-bound form.

Animals↗
PubMed1983

[Some properties of peptidase from rat heart, breaking down luliberin].

The properties of rat heart peptidase hydrolyzing luliberin were studied. This peptidase was shown to be a sulfhydryl metalloenzyme with m.w. of about 100000. The maximal enzyme activity was observed at neutral values of pH Ca2+ (5 X 10(-6) M) increased the enzyme activity by 50%, thus being indicative of an anomalous dependence of the enzyme activity of substrate concentration. At luliberin concentrations of 10(-7)-10(-6) M the enzyme activation by Ca2+ was considerably reduced and returned to the initial level when the peptide concentration was increased up to 10(-5) M. It was assumed that the peptidase under study is a regulatory enzyme whose activity depends on concentrations of Ca2+ and of the reaction substrate, luliberin.

Animals↗
PubMed1984

Bacterial wall peptidoglycan, DD-peptidases and beta-lactam antibiotics.

Wall peptidoglycan expansion in bacteria rests upon a cytoplasmic D-Ala: D-Ala ligase (ADP) which catalyses synthesis of a D-Ala-D-Ala dipeptide (with accompanying hydrolysis of one molecule of ATP) and a set of DD-peptidases which utilize this D-Ala-D-Ala dipeptide--once it has been translocated at the outer face of the plasma membrane as the C-terminal portion of a disaccharide peptide unit--as carbonyl donor for transpeptidation and carboxypeptidation reactions (without additional energy expenditure). Four DD-peptidases have been selected which differ from each other with respect to the effects that amino compounds exert on the fate and rate of consumption of a D-Ala-D-Ala terminated amide carbonyl donor analogue. They serve as models to understand the different mechanisms by which the DD-peptidases perform catalysis and show widely varying responses to the action of beta-lactams, from extreme sensitivity to very high resistance.

Amino Acyl-tRNA Synthetases↗
PubMed1994

Effect of peptidases at the blood brain barrier on the permeability of enkephalin.

The blood brain barrier (BBB) presents an enzymatic barrier to the passage of peptides, from blood to brain. The studies presented here used a well established in vitro model of the BBB to measure the presence of peptidases and the permeability of two opioid peptides. The in vitro BBB model consisted of confluent monolayers of bovine brain microvessel endothelial cells (BMECs). Enkephalin metabolizing enzymes, total aminopeptidase, aminopeptidase M (APM), angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) activities were measured in BMEC monolayers. The effect of specific inhibitors of APM, ACE and NEP on the permeability of [Met5]enkephalin (Met-Enk) and a conformationally constrained and enzymatically stable analog, DPDPE, also was determined. High levels of membrane-associated enzyme activity were measured for total aminopeptidase, APM and ACE. Interestingly, the permeability coefficient of Met-Enk was increased 4-fold in the presence of specific inhibitors of APM and ACE. Low levels of NEP activity were measured in BMEC monolayers and inhibition of NEP had no effect on Met-Enk permeability. The permeability coefficient for DPDPE was not increased with enzyme inhibitors but was 4-fold greater than Met-Enk alone. In the presence of APM or ACE inhibitors, there was no difference in the permeability of DPDPE and Met-Enk. These experiments demonstrate the presence of specific peptidases in BMECs and that the presence of inhibitors to Met-Enk inactivating peptidases significantly increased permeability of this biologically active peptide.

Amino Acid Sequence↗
PubMed1993

Membrane topology and biogenesis of eukaryotic signal peptidase.

The signal peptidase complex (SPC) is a hetero-oligomeric membrane protein containing subunits of 12, 18, 21, 22/23, and 25 kDa. The 18- and 21-kDa subunits are mammalian homologs of SEC11 protein, which is necessary for signal peptide processing and cell viability in the yeast Saccharomyces cerevisiae. The functional and/or structural contributions of the 12-, 22/23-, and 25-kDa subunits to SPC activity have not yet been elucidated. To explore the structure of SPC subunits and their relationships to signal peptide processing and protein translocation, we have examined their endoplasmic reticulum (ER) membrane topology and biogenesis. Signal peptidase activity and SPC subunits are resistant to protease treatment in intact and detergent-solubilized membranes. Heat-denatured SPC subunits and SPC subunits translated in vitro are, however, protease sensitive, suggesting that the assembly of the oligomeric complex confers protease resistance. To define the membrane topology of SPC subunits, both wild-type subunits and subunit fusion proteins containing additional sites for N-linked glycosylation were assembled into microsomal membranes in vitro. Despite the presence of multiple hydrophobic domains, each subunit is anchored to the ER membrane by a single amino-terminal transmembrane domain in an Ncytoplasmic Cexoplasmic (type II) orientation. This topology places the bulk of the protein mass in the ER lumen and positions a putative serine-containing active site domain in SPC 18 and 21 at the same relative distance from the membrane as the analogous region in Escherichia coli leader peptidase. These studies have also revealed that, in spite of the temporal and perhaps physical association of the SPC with the process of protein translocation, SPC subunits integrate into the ER membrane by a signal recognition particle-dependent pathway and, hence, rely on the existence of a preformed translocation apparatus for their own membrane assembly.

Amino Acid Sequence↗
PubMed1993

Human coagulation factor X deficiency caused by a mutant signal peptide that blocks cleavage by signal peptidase but not targeting and translocation to the endoplasmic reticulum.

Human factor XSanto Domingo is a form of coagulation factor X in which a mutation within the signal peptide region of the precursor protein has been correlated genetically with a severe deficiency of factor X in the affected individual. A point mutation results in substitution of Arg for Gly at the critical -3 position of the factor X signal peptide. To determine the biochemical effect of this mutation on the biosynthesis of factor X, the wild-type and mutant factor X cDNAs were subcloned into a vector for transcription and translation in vitro. Translation products of mRNAs encoding portions of both mutant and wild-type proteins were used in a systematic biochemical approach to evaluate directly the effect of the mutation on targeting, transport, and proteolytic processing in vitro. The results show that targeting and transport of factor XSanto Domingo to the endoplasmic reticulum are functionally dissociated from the removal of the signal peptide by signal peptidase. Factor XSanto Domingo is translocated into the endoplasmic reticulum but not processed by signal peptidase. Transient expression of the wild-type and mutant factor X in human embryonic kidney 293 cells revealed apparently normal secretion of the glycosylated two-chain form of factor X but no secretion of factor XSanto Domingo. Thus, the inability of signal peptidase to cleave factor XSanto Domingo is directly responsible for the absence of circulating factor X and leads to the bleeding diathesis in the affected individual.

Amino Acid Sequence↗
PubMed1996

Taenia saginata oncosphere excretory/secretory peptidases.

To identify oncosphere excretory/secretory peptidases, Taenia saginata adult worms were collected from 3 patients. Eggs were hatched and activated in vitro and oncospheres cultured in vitro. The culture medium from the oncospheres was assayed with peptide substrates coupled to 7-amino-4-trifluoromethyl coumarin (AFC), and free AFC was detected fluorometrically. The endopeptidase substrates Z-Phe-Arg-AFC and Z-Arg-AFC as well as the aminopeptidase substrate Arg-AFC were hydrolyzed when incubated with spent media from the oncospheres compared to control culture medium removed prior to incubation. Hydrolysis of Z-Phe-Arg-AFC was inhibited 78% by preincubation of the medium with the serine proteinase inhibitor Phenylmethylsulfonyl fluoride. Endopeptidase activity was partially enhanced in the presence of exogenous thiols and partially inhibited with the cysteine proteinase inhibitor E-64, suggesting the presence of both serine and cysteine endopeptidases. No significant inhibition was noted with pepstatin or phenanthroline. The peptidase activities detected with Z-Phe-Arg-AFC and Arg-AFC were separated by gel-filtration fast protein liquid chromatography and eluted at volumes corresponding to molecular weights of 18 and 30 kDa, respectively. These data demonstrate that T. saginata oncospheres produce excretory/secretory peptidases, including serine and cysteine endopeptidases and an aminopeptidase. These enzymes may play a role in invasion of the intestinal mucosa of the intermediate host.

Amino Acid Sequence↗