A novel endopeptidase with a strict specificity for threonine residues at the P1' position

An endopeptidase was purified from Archachatina ventricosa by chromatography on columns of gel filtration, DEAE-Sepharose and phenyl-Sepharose. The preparation was shown to be homogeneous by polyacrylamide gel electrophoresis and capillary electrophoresis. The purified enzyme displayed two protein bands on SDS-polyacrylamide gel electrophoresis with estimated molecular weights of 90,000 and 121,000. The protease exhibited maximum proteolytic activity at 55 degrees C and at pH 8.0, but it retained more than 85% of its activity in the pH range 7.5 to 8.5. It was completely inactivated by the chelating agents EDTA and 1,10-phenanthroline which are metalloprotease inhibitors. Studies on substrate specificity showed that only the amide bonds of peptide substrates having a threonine residue at the P1' position were hydrolyzed by the purified protease. This endopeptidase constitutes a novel tool for the study of proteins in view of its narrow and unique substrate specificity.     

Purification of a liver alkaline protease which degrades oxidatively modified glutamine synthetase. Characterization as a high molecular weight cysteine proteinase

A nonlysosomal alkaline protease which degrades the oxidatively modified form of Escherichia coli glutamine synthetase has been purified to apparent homogeneity from rat and mouse liver acetone powders. Its molecular weight was determined to be 300,000 by Sephacryl S-300 gel filtration but results of further studies using high pressure liquid chromatography gel filtration suggest a value of 650,000. Examination of the subunit structure by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed multiple bands of molecular weights between 22,000 and 34,000. The alkaline protease was inhibited by thiol reagents. Phenylmethylsulfonyl fluoride, aprotinin, leupeptin, antipain, and chymostatin partially inhibited the protease. The inhibition by phenylmethylsulfonyl fluoride was prevented by dithiothreitol, and alpha 1-antitrypsin and soybean trypsin inhibitor did not inhibit. No inhibition was observed with metalloprotease inhibitors. The alkaline protease is active over a broad range of pH with optimum activity for the degradation of oxidized glutamine synthetase around pH 9.0. Its activity is not stimulated by MgATP. A study of the products of insulin B chain degradation demonstrated major cleavage sites at Gln13-Ala14, Leu15-Tyr16, Cys(SO3H)19-Gly20, Gln4-His5, and Leu17-Val18. Based on its endopeptidase activity and its inhibitor specificity, the alkaline protease should be classified as a cysteine proteinase. It appears to be distinct from previously described proteinases and is likely involved in nonlysosomal mechanisms of intracellular protein turnover.     

A human serine endopeptidase, purified with respect to activity against a peptide with phosphoserine in the P1' position, is apparently identical with prolyl endopeptidase

The present work describes the detection, purification, and characterization of a serine endopeptidase with preference for a phosphoserine in the P1' position of the substrate. During probing for the enzyme in crude extracts, as well as during its 64,000-fold purification, 32P-labeled guanidovaleryl-Arg-Ala-Ser(P)-isobutyl amide (I) was used to measure the cleavage of the Ala-Ser(P) bond. With this substrate, kcat was 1.7 s-1 and Km was 30 microM at the pH optimum, 7.5. The enzyme was classified as a serine peptidase from its reaction with a set of inhibitors, among which diisopropyl fluorophosphate was effective at low (20 microM) concentration. The endopeptidase showed an Mr of 74,000 under native as well as denaturing and reducing conditions, indicating that the native enzyme consists of only one major polypeptide chain. The molecular size and inhibition profile suggested identity of this enzyme with prolyl endopeptidase (EC 3.4.21.26). This was supported by its activity against specific substrates, such as succinyl-Gly-Pro-Leu-Pro-7-amido-4-methylcoumarin (kcat = 7.2 s-1 and Km = 290 microM), and by the inhibition of the latter activity by I. Compared with the cleavage of 100 microM I, Gly-Val-Leu-Arg-Arg-Ala-Ser-Val-Ala-Gln-Leu, after phosphorylation by cAMP-dependent protein kinase, was cleaved at the Ala-Ser(P) bond at a relative rate of 0.43, while cleavage of the Ala-Ser bond of the unphosphorylated undecapeptide was undetectable, i.e. less than 0.03. The pentapeptide Arg-Arg-Pro-Ser-Val was rapidly cleaved at the Pro-Ser bond (relative rate, 2.2). Still, the cleavage of the Pro-Ser(P) bond of the corresponding phosphorylated pentapeptide was even higher (relative rate, 4.0). These data suggest that phosphorylation of a serine residue in the P1' position of at least a few substrates of prolyl endopeptidase will increase the rate of their cleavage.     

Purification and properties of the thermostable acid protease of Penicillium duponti.

An acid protease produced by the thermophilic fungus Penicillium duponti K 1014 has been purified by consecutive ion-exchange and gel permeation chromatography, and crystallized from aqueous acetone solution. The purified endopeptidase gave a symmetrical schlieren peak by sedimentation velocity, and was found to be homogeneous upon disc gel electrophoresis at pH 9.5. The enzyme was most active at pH 2.5 against milk casein and showed high thermostability. An isoelectric point of 3.81 was found by isoelectric focusing. A minimum molecular weight of 41 590 was calculated from the amino acid composition, adopting an arginine content of one residue per mole of enzyme. This minimum molecular weight is in good agreement with the value of 41 000 previously found by gel permeation (Hashimoto, H., Iwaasa, T., and Yokotsuka, T. (1973), Appl. Microbiol. 25, 578). Besides the thermostability, the purified P. duponti protease differs from other well-characterized acid proteases in that it contains carbohydrate, 4.33% expressed as glucose. The enzyme was not affected by p-bromophenacyl bromide, but was completely inactivated by alpha-diazo-p-bromoacetophenone, diazoacetyl-DL-norleucine methyl ester, and diazoacetylglycine ethyl ester, in the presence of Cu2+. The complete inactivation of the protease by diazoacetyl-DL-norleucine methyl ester resulted in the specific incorporation of 1 mol of norleucine/mol of enzyme. On the basis of similar behavior of other acid proteases toward this inactivator, the results suggest the presence at the active site of an unusually reactive carboxyl group, involved in the catalytic function. The naturally occurring pepsin inhibitor of Streptomyces naniwaensis [Murao, S., and Satoi, S. (1970), Agric. Biol. Chem. 34, 1265] inhibited also the protease, at a threefold molar excess with respect to the enzyme.     

The HtrA (DegP) protein, essential for Escherichia coli survival at high temperatures, is an endopeptidase.

As a preliminary step in the understanding of the function of the Escherichia coli HtrA (DegP) protein, which is indispensable for bacterial survival only at elevated temperatures, the protein was purified and partially characterized. The HtrA protein was purified from cells carrying the htrA gene cloned into a multicopy plasmid, resulting in its overproduction. The sequence of the 13 N-terminal amino acids of the purified HtrA protein was determined and was identical to the one predicted for the mature HtrA protein by the DNA sequence of the cloned gene. Moreover, the N-terminal sequence showed that the 48-kilodalton HtrA protein is derived by cleavage of the first 26 amino acids of the pre-HtrA precursor polypeptide and that the point of cleavage follows a typical target sequence recognized by the leader peptidase enzyme. The HtrA protein was shown to be a specific endopeptidase which was inhibited by diisopropylfluorophosphate, suggesting that HtrA is a serine protease.     

Purification and characterization of cathepsin B from monkey skeletal muscle

Cathepsin B was purified about 11,000-fold from monkey skeletal muscle by ammonium sulfate fractionation and sequential column chromatographies monitored by assaying of Z-Phe-Arg-MCA hydrolase activity. The purified enzyme gave a single protein band on SDS-polyacrylamide gel electrophoresis, and its molecular weight was estimated to be 24,000 by gel filtration. It had a pH optimum of 6.5, required a thiol reducing agent for activation, and was inhibited by various thiol protease inhibitors. These properties were similar to those reported for cathepsins B from other sources. Although the enzyme scarcely hydrolyzed ordinary proteins, such as casein, hemoglobin, and bovine serum albumin, it degraded myosin and actin among various myofibrillar proteins. These results strongly suggested that skeletal muscle cathepsin B may participate in the degradation of muscle proteins in vivo. In addition, cathepsin B was shown to hydrolyze various neuropeptides such as Leu-enkephalin, beta-neoendorphin, alpha-neoendorphin, dynorphin(1-13), and substance P. It appeared to act on these peptides mainly as a dipeptidyl carboxypeptidase, although not so rigorously, presumably due to its endopeptidase activity.     

The unique sites in SulA protein preferentially cleaved by ATP-dependent Lon protease from Escherichia coli.

SulA protein is known to be one of the physiological substrates of Lon protease, an ATP-dependent protease from Escherichia coli. In this study, we investigated the cleavage specificity of Lon protease toward SulA protein. The enzyme was shown to cleave approximately 27 peptide bonds in the presence of ATP. Among them, six peptide bonds were cleaved preferentially in the early stage of digestion, which represented an apparently unique cleavage sites with mainly Leu and Ser residues at the P1, and P1' positions, respectively, and one or two Gln residues in positions P2-P5. They were located in the central region and partly in the C-terminal region, both of which are known to be important for the function of SulA, such as inhibition of cell growth and interaction with Lon protease, respectively. The other cleavage sites did not represent such consensus sequences, though hydrophobic or noncharged residues appeared to be relatively preferred at the P1 sites. On the other hand, the cleavage in the absence of ATP was very much slower, especially in the central region, than in the presence of ATP. The central region was predicted to be rich in alpha helix and beta sheet structures, suggesting that the enzyme required ATP for disrupting such structures prior to cleavage. Taken together, SulA is thought to contain such unique cleavage sites in its functionally and structurally important regions whose preferential cleavage accelerates the ATP-dependent degradation of the protein by Lon protease.     

Endosomal proteolysis of internalized insulin at the C-terminal region of the B chain by cathepsin D.

The endosomal compartment of hepatic parenchymal cells contains an acidic endopeptidase, endosomal acidic insulinase, which hydrolyzes internalized insulin and generates the major primary end product A(1--21)-B(1--24) insulin resulting from a major cleavage at residues Phe(B24)-Phe(B25). This study addresses the nature of the relevant endopeptidase activity in rat liver that is responsible for most receptor-mediated insulin degradation in vivo. The endosomal activity was shown to be aspartic acid protease cathepsin D (CD), based on biochemical similarities to purified CD in 1) the rate and site of substrate cleavage, 2) pH optimum, 3) sensitivity to pepstatin A, and 4) binding to pepstatin A-agarose. The identity of the protease was immunologically confirmed by removal of greater than 90% of the insulin-degrading activity associated with an endosomal lysate using polyclonal antibodies to CD. Moreover, the elution profile of the endosomal acidic insulinase activity on a gel-filtration TSK-GEL G3000 SW(XL) high performance liquid chromatography column corresponded exactly with the elution profile of the immunoreactive 45-kDa mature form of endosomal CD. Using nondenaturating immunoprecipitation and immunoblotting procedures, other endosomal aspartic acid proteases such as cathepsin E and beta-site amyloid precursor protein-cleaving enzyme (BACE) were ruled out as candidate enzymes for the endosomal degradation of internalized insulin. Immunofluorescence studies showed a largely vesicular staining pattern for internalized insulin in rat hepatocytes that colocalized partially with CD. In vivo pepstatin A treatment was without any observable effect on the insulin receptor content of endosomes but augmented the phosphotyrosine content of the endosomal insulin receptor after insulin injection. These results suggest that CD is the endosomal acidic insulinase activity which catalyzes the rate-limiting step of the in vivo cleavage at the Phe(B24)-Phe(B25) bond, generating the inactive A(1--21)-B(1--24) insulin intermediate.     

Purification and characterization of a substance P-degrading endopeptidase from rat brain

A novel substance P-degrading endopeptidase has been solubilized with Brij 35 from a membrane fraction of rat brain and purified by a procedure involving DEAE-cellulose chromatography, hydroxyapatite chromatography, Sephadex G-100 gel filtration, and Mono-Q HPLC. The activity of the degrading enzyme was monitored by measuring the disappearance of substance P by means of a bioassay and HPLC. SDS-polyacrylamide gel electrophoresis under reducing conditions of the enzyme gave a single band corresponding to a molecular weight of 58,000. The molecular weight of the enzyme was estimated to be 55,000 by gel filtration and the optimum pH for its activity was 7.5.. The purified enzyme cleaved substance P at three bonds, Pro4-Gln5, Gln5-Gln6, and Gln6-Phe7, in the ratio of 2:2:3. EDTA, o-phenanthroline, and p-chloromercuribenzenesulfonic acid strongly inhibited the enzyme, while diisopropyl fluorophosphate, E-64, Z-Gly-ProCH2Cl, phosphoramidon, and captopril had little or no inhibitory effect on it. The cleavage of substance P by the rat brain synaptic membrane was also analyzed under the conditions with or without these inhibitors. The inhibitor-susceptibility of the cleavage sites suggests that the present enzyme, together with endopeptidase-24.11, is involved in the degradation of substance P in the synaptic region.     

An endopeptidase associated with bovine neurohypophysis secretory granules cleaves pro-ocytocin/neurophysin peptide at paired basic residues

The octacosapeptide sequence [Tyr18] pro-ocytocin/neurophysin (1-18)NH2 [pro-OT/Np(1-18)NH2] was synthesized and used as substrate to detect endoprotease(s) possibly involved in the processing of this precursor in bovine hypothalamo-neurohypophyseal tract. An endopeptidase (58 Kda) was detected in Lysates made from highly purified neurosecretory granules. This protease which cleaves the peptide bond on the carboxyl side of the Lys-Arg doublet, and no single basic residue, generates both OT-Gly10-Lys11-Arg12+Ala13-Val-Leu-Asp-Leu-Tyr18 (NH2) from the octacosapeptide substrate. In addition, a carboxypeptidase B-like activity converting OT-Gly10-Lys11-Arg12 into OT-Gly10 was detected in the same granule Lysates. It is hypothesized that a combination of these endoprotease and carboxypeptidase B-like activities together with the amidating enzyme of secretory granules might participate in the cleavage and processing of pro-OT/Np in vivo.     

Protease II from Escherichia coli: sequencing and expression of the enzyme gene and characterization of the expressed enzyme.

Protease II gene of Escherichia coli HB101 was cloned and expressed in E. coli JM83. The transformant harboring a hybrid plasmid, pPROII-12, with a 2.4 kbp fragment showed 90-fold higher enzyme activity than the host. The whole nucleotide sequence of the inserted fragment of plasmid pPROII-12 was clarified by the dideoxy chain-terminating method. The sequence that encoded the mature enzyme protein was found to start at an ATG codon, as judged by comparison with amino terminal protein sequencing. The molecular weight of the enzyme was estimated to be 81,858 from the nucleotide sequence. The reactive serine residue of protease II was identified as Ser-532 with tritium DFP. The sequence around the serine residue is coincident with the common sequence of Gly-X-Ser-X-Gly, which has been found in the active site of serine proteases. Except for this region, protease II showed no significant sequence homology with E. coli serine proteases, protease IV and protease La (lon gene), or other known families of serine proteases. However, 25.3% homology was observed between protease II and prolyl endopeptidase from porcine brain. Although the substrate specificities of these two enzymes are quite different, it seems possible to classify protease II as a member of the prolyl endopeptidase family from the structural point of view.     

Purification of an endopeptidase involved with storage-protein degradation in Phaseolus vulgaris L. cotyledons

Phaseolin, the major seed storage protein of Phaseolus vulgaris L., is degraded in the cotyledons in the first 7–10 d following seed germination. We assayed cotyledon extracts for protease activity by using [³H]phaseolin as a substrate and then fractionated the digestion mixtures by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in order to identify the cleavage products. The cotyledons of 4-d-old seedlings contain an endopeptidase which cleaves the polypeptides of [³H]phaseolin (apparent molecular weights=51 000, 48 000, 46 000 and 43 000) into three discrete clusters of proteolytic fragments (M _rs=27 000, 25 000 and 23 000). Endopeptidase activity is not detected in the cotyledons until the protein content of these organs starts to decline, shortly after the first day of seedling growth. Endopeptidase activity increases to a maximum level in the cotyledons of 5-d-old seedlings and then declines to a minimum value by day 10. The enzyme was purified 335-fold by ammonium-sulfate precipitation, organomercurial-agarose chromatography, gel filtration and ion-exchange chromatography. The endopeptidase constitutes 0.3% of the protein content in the cotyledons of 4-d-old seedlings. It is a cysteine protease with a single polypeptide chain (M _r=30 000). Optimum hydrolysis of [³H]phaseolin occurs at pH 5. The enzyme is irreversibly inactivated at pH values above 7 and at temperatures above 45° C. The endopeptidase attacks only a limited number of peptide bonds in [³H]phaseolin, without causing any appreciable change in the native molecular weight of the storage protein. The endopeptidase is also able to hydrolyze the bean-seed lectin, phytohemagglutinin. Thus, this enzyme may play a general role in degrading cotyledon proteins of P. vulgaris following seed germination.Abbreviations Da dalton - DTT dithiothreitol - M _r apparent molecular weight - PAGE polyacrylamide gel electrophoresis - PHA phytohemagglutinin - SDS sodium dodecyl sulfate     

Characterization of an endopeptidase of Trypanosoma brucei brucei.

A soluble 80-kDa endopeptidase has been isolated from Trypanosoma brucei brucei. The enzyme, which has a pI 5.1, is optimally active at about pH 8.2 and has apparent pKa values of 6.0 and greater than or equal to 10. It is inhibited by the serine protease inhibitor diisopropylfluorophosphate and by the serine protease mechanism-based inhibitor 3,4-dichloroisocoumarin. Unexpectedly, the enzyme is inhibited by the cysteine protease inhibitor benzyloxycarbonyl-Leu-Lys-CHN2 but not by the related diazomethane, butoxycarbonyl-Val-Leu-Gly-Lys-CHN2, nor by other cysteine protease specific compounds. Specificity studies with a variety of amidomethylcoumaryl (AMC) derivatives of small peptides show that the enzyme has a highly restricted trypsin-like specificity. The best substrate, based on the magnitude of kcat/Km, was benzyloxycarbonyl-Arg-Arg-AMC; other good substrates were benzyloxycarbonyl-Phe-Arg-AMC, benzoyl-Arg-AMC, and compounds with Arg at P1 and Ala or Gly at P2. The hydrolysis of most substrates obeyed classical Michaelis-Menton kinetics but several exhibited pronounced substrate inhibition. The enzyme did not activate plasminogen nor decrease blood clotting time; it was inhibited by aprotinin but not by chicken ovomucoid. We conclude that the enzyme is a trypsin-like serine endopeptidase with unusually restricted subsite specificities.     

Specific cleavage of DNA at CG sites by Co(III) and Ni(II) desferal complexes.

Hydrolysis of endothelin 1 by rat kidney membranes was investigated using a reverse-phase HPLC and an automated gas-phase protein sequencer. Endothelin 1 was hydrolyzed into four major fragments which were detected by HPLC. Phosphoramidon, an inhibitor of neutral endopeptidase 24,11, almost completely suppressed the production of three fragments, but one fragment was not affected by the inhibitor. Analysis of N-terminal sequences of the degradation products revealed that the phosphoramidon-sensitive fragments were generated by cleavage at the Ser5-Leu6 bond of endothelin 1 that was identical with its cleavage site by purified rat endopeptidase 24,11, reported previously. The phosphoramidon-insensitive fragment was produced by cleavage at Leu17-Asp18, which was distinct from the sites by endopeptidase 24,11, but corresponded to that by a phosphoramidon-insensitive metallo-endopeptidase recently isolated from rat kidney membranes by us [(1992) Eur. J. Biochem. 204, 547-552]. Kinetic determination of endothelin 1 hydrolysis by the isolated enzyme yielded values of Km = 71.5 microM and kcat = 1.49 s-1, giving a ratio of kcat/Km = 2.08 x 10(4) s-1.M-1. The Km value was much higher and the kcat/Km value was much lower than those for rat endopeptidase 24,11 reported previously. Thus, endopeptidase 24,11 appears to hydrolyze endothelin 1 more efficiently than the isolated enzyme does. Both enzymes may play physiological roles in the metabolism of endothelin 1 by rat kidney membranes in vivo.     

Overexpression and characterization of a prolyl endopeptidase from the hyperthermophilic archaeon Pyrococcus furiosus.

The maltose-regulated mlr-2 gene from the hyperthermophilic archaeon Pyrococcus furiosus having homology to bacterial and eukaryal prolyl endopeptidase (PEPase) was cloned and overexpressed in Escherichia coli. Extracts from recombinant cells were capable of hydrolyzing the PEPase substrate benzyloxycarbonyl-Gly-Pro-p-nitroanilide (ZGPpNA) with a temperature optimum between 85 and 90 degrees C. Denaturing gel electrophoresis of purified PEPase showed that enzyme activity was associated with a 70-kDa protein, which is consistent with that predicted from the mlr-2 sequence. However, an apparent molecular mass of 59 kDa was obtained from gel permeation studies. In addition to ZGPpNA (K(Mapp) of 53 microM), PEPase was capable of hydrolyzing azocasein, although at a low rate. No activity was detected when ZGPpNA was replaced by substrates for carboxypeptidase A and B, chymotrypsin, subtilisin, and neutral endopeptidase. N-[N-(L-3-trans-Carboxirane-2-carbonyl)-L-Leu]-agmatine (E-64) and tosyl-L-Lys chloromethyl ketone did not inhibit PEPase activity. Both phenylmethylsulfonyl fluoride and diprotin A inhibited ZGPpNA cleavage, the latter doing so competitively (K(lapp) of 343 microM). At 100 degrees C, the enzyme displayed some tolerance to sodium dodecyl sulfate treatment. Stability of PEPase over time was dependent on protein concentration; at temperatures above 65 degrees C, dilute samples retained most of their activity after 24 h while the activity of concentrated preparations diminished significantly. This decrease was found to be due, in part, to autoproteolysis. Partially purified PEPase from P. furiosus exhibited the same temperature optimum, molecular weight, and kinetic characteristics as the enzyme overexpressed in E. coli. Extracts from P. furiosus cultures grown in the presence of maltose were approximately sevenfold greater in PEPase activity than those grown without maltose. Activity could not be detected in clarified medium obtained from maltose-grown cultures. We conclude that mlr-2, now called prpA, encodes PEPase; the physiological role of this protease is presently unknown.     

Proteolysis in heat-stressed HeLa cells. Stabilization of ubiquitin correlates with the loss of proline endopeptidase

When intact HeLa cells were incubated at 45 degrees C, there was progressive inactivation of proline endopeptidase. Rapid loss of the enzyme did not occur in extracts maintained at 45 degrees C. Since Western blots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels showed no decrease in the immunoreactive 70-kDa proline endopeptidase band, its in vivo disappearance apparently results from irreversible denaturation or modification. Loss of proline endopeptidase activity was paralleled by reduced degradation of injected ubiquitin and bovine serum albumin. In contrast, proteolysis of injected lysozyme or pancreatic trypsin inhibitor was barely affected. Electrophoretic analysis of ubiquitin or bovine serum albumin retrieved from heated HeLa cells showed that the injected proteins were intact. Thus, the presence of proline endopeptidase appears to be required for initial cleavage of these two substrates, but it has not been shown that the enzyme is directly responsible. Selective stabilization of a subset of the injected proteins does, however, demonstrate the existence of distinct proteolytic pathways in HeLa cytosol.     

Purification and characterization of the mouse mammary tumor virus protease expressed in Escherichia coli.

The mouse mammary tumor virus (MMTV) protease gene was cloned into pGEX-2T, an Escherichia coli expression vector containing the glutathione S-transferase coding region of Schistosoma japonicum. The chimeric protein was formed by fusion of the glutathione S-transferase with a hexapeptide which contains a thrombin cleavage site, followed by the MMTV protease. Affinity chromatography on a glutathione-Sepharose 4B column was used to isolate the chimeric protein. After thrombin cleavage, the glutathione S-transferase and the protease were separated by gel filtration chromatography on a Sephadex G-75 column. The overall yield of the protease purification procedure was about 1 mg of protease/liter of culture, and the specific activity was 380 pmol/min.micrograms of enzyme. Like other retroviral proteases, the MMTV enzyme was active as a dimer, showed maximum activity at pH between 4 and 6, and could be inhibited by pepstatin A and a phosphinic acid derivative HIV-1 protease inhibitor. Enzymatic characterization of this protease reveals its broad specificity, showing a clear preference for the oligopeptide substrate mimicking the cleavage site at the amino-terminal end of the capsid protein (kcat/Km = 9725.5 M-1.s-1). The chimeric protein was also an active dimer and showed a similar Km (17 microM) for such an oligopeptide, although its kcat was about 10 times smaller. Autocatalytic processing of the MMTV protease was observed after expression of clones containing the natural cleavage site, as it occurs at the amino-terminal end of the viral protease, instead of the thrombin-sensitive sequence.     

Purification and characterization of the yeast glycosylphosphatidylinositol-anchored, monobasic-specific aspartyl protease yapsin 2 (Mkc7p).

The Saccharomyces cerevisiae YPS2 (formerly MKC7) gene product is a glycosylphosphatidylinositol-linked aspartyl protease that functions as a yeast secretase. Here, the glycosylphosphatidylinositol-linked form of yapsin 2 (Mkc7p) was purified to homogeneity from the membrane fraction of an overexpressing yeast strain. Purified yapsin 2 migrated diffusely in SDS-polyacrylamide gel electrophoresis (molecular mass approximately 200 kDa), suggesting extensive, heterogeneous glycosylation. Studies using internally quenched fluorogenic peptide substrates revealed cleavage by the enzyme carboxyl to Lys or Arg. No cleavage was seen when both Lys and Arg were absent. No significant enhancement was seen with multiple basic residues. However, cleavage always occurred carboxyl to the most COOH-terminal basic residue. V(max)/K(m) was insensitive to P(2) and P(3) residues except that Pro at P(2) blocked cleavage entirely. These results suggest that yapsin 2 is a monobasic amino acid-specific protease that requires a basic residue at P(1) and excludes basic residues from P(1)'. The pH dependence of V(max)/K(m) for a substrate containing a pro-alpha factor cleavage site was bell-shaped, with a maximum near pH 4.0. However, V(max)/K(m) for a substrate mimicking the alpha-secretase site in human beta amyloid precursor protein was optimal near pH 6.0, consistent with cleavage of beta amyloid precursor protein by yapsin 2 when expressed in yeast.     

Purification and characterization of a calcium-activated neutral protease from monkey brain and its action on neuropeptides

A calcium-activated neutral protease was purified from Japanese monkey brain by ammonium sulfate fractionation and sequential column chromatographies monitored by assay of caseinolytic activity. The purified enzyme gave a single protein band on non-denaturing polyacrylamide gel electrophoresis, and consisted of two subunits with molecular weights of 74,000 and 20,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme required millimolar order calcium ions for activation, and was optimally active at pH 7.5-8.0. Upon incubation with various neuropeptides as substrates, the enzyme preferentially cleaved the peptide bonds with Arg, Lys, or Tyr at the P1 position and an amino acid residue with a bulky aliphatic side chain, such as Leu, Val, or Ile, at the P2 position. The hydrolytic activity toward neuropeptides as well as casein was strongly inhibited by various thiol protease inhibitors. These results suggested that the brain calcium-activated neutral protease may participate in the degradation of neuropeptides in vivo.     

Purification and characterization of prolyl endopeptidase from pig brain

The prolyl endopeptidase from pig brain was purified to homogeneity according to SDS-gel electrophoresis and visualization with the silver staining procedure. The molecular weight of prolyl endopeptidase was estimated as 70 kDa, and the isoelectric point as 4.9. The molecular properties of prolyl endopeptidase from pig brain are therefore similar to those of prolyl endopeptidases from other mammalian tissues. Diisopropylfluorophosphate, diethylpyrocarbonate and p-chloromercuribenzoic acid are strong irreversible inhibitors of prolyl endopeptidase from pig brain. We showed that diisopropylfluorophosphate und diethylpyrocarbonate act as competitive inhibitors with respect to substrate. Therefore it is assumed that at least one serine and one histidine residue are located at the active site of this enzyme. This result supports the assumption that the prolyl endopeptidase from pig brain is a typical serine protease. Substance P, thyreoliberin, beta-casomorphin-5 and morphiceptin are hydrolysed by prolyl endopeptidase in vitro.