Synthesis of lysine-containing sulphonium salts and their properties as proteinase inhibitors.

Some sulphonium salts derived from lysine were synthesized with the general structure R-Lys-CH2S+-(alkyl)2. They were examined as inhibitors of the cysteine proteinase clostripain, which has a preference for cleaving peptide bonds at the carboxy group of basic amino acids, and of a number of trypsin-related serine proteinases. Clostripain was irreversibly inactivated by all reagents examined, but in the case of the serine proteinases, depending on the reagent structure, irreversible and reversible inhibitions were observed. These were kinetically characterized.     

Pseudoarginine: synthesis and properties of derivatives of delta-(1-imidazolyl)norvaline.

An analogue of arginine has been synthesized in which an imidazole ring occupies the position of the guanidino group of the natural amino acid. It was expected that peptides containing this amino acid when protonated might bind at enzymic sites specific for arginine, but that the pK of the imidazole ring, near 7, would facilitate entry of such peptides into cells, in contrast to peptides containing arginine. Other analogues of arginine can be visualized with a low side-chain pK, including isomers of the imidazole derivative which is the subject of this paper. These are viewed as 'pseudoarginines'. Our initial observations concern the properties of delta-(1-imidazolyl)norvaline in which a ring nitrogen atom is attached to norvaline, which thus becomes comparable to the guanidino delta-nitrogen. Its synthesis is described along with several derivatives examined as substrates or inhibitors. Potential ligands containing delta-(1-imidazolyl)norvaline (ImNva) did not give evidence of interaction with trypsin or plasma kallikrein, serine proteinases which bind arginine derivatives. However, clostripain, a bacterial cysteine proteinase specific for arginine, was readily inactivated by Cbz-Phe-ImNva-CH2F and the rate of inactivation showed an acid pH-dependence not observed, for example, in the inactivation of clostripain by Bz-Phe-LysCH2F.     

The synthesis and properties of peptidylmethylsulphonium salts with two cationic residues as potential inhibitors of prohormone processing.

Peptidylmethylsulphonium salts incorporating consecutive basic residues at the C-terminus of the peptidyl portion such as -Arg-Arg-, -Arg-Lys-, -Lys-Lys- and -Lys-Arg- were synthesized and examined as proteinase inhibitors. Serine proteinases with a specificity directed towards hydrolysis at cationic residues were found to be unaffected by these derivatives. On the other hand, cysteine proteinases, cathepsin B and, in particular, clostripain were readily inactivated by affinity labelling. The reagents thus are of promise for the study of prohormone processing promoted by cysteine proteinases.     

Cystatin S: a cysteine proteinase inhibitor of human saliva

An acidic protein of human saliva, which we named SAP-1 previously, is now shown to be an inhibitor of several cysteine proteinases. The protein inhibited papain and ficin strongly, and stem bromelain and bovine cathepsin C partially. However, it did not inhibit either porcine cathepsin B or clostripain. The mode of the inhibition of papain was found to be non-competitive. The name cystatin S has been proposed for this salivary protein in view of the similarities in activity and structure to other cysteine proteinase inhibitors such as chicken egg-white cystatin and human cystatins A, B, and C. The cystatin S antigen was detected immunohistochemically in the serous cells of human parotid and submaxillary glands.     

Isolation and partial characterisation of a thiol proteinase inhibitor from human plasma.

A thiol proteinase inhibitor has been isolated from human plasma by ion exchange, salt-mediated hydrophobic and ion chelation chromatography. It was found to be electrophoretically heterogeneous (in both its native state and after isolation) giving a bimodal arc with an α₁ and α₂ peak in bidimensional immunoelectrophoresis. It was a good inhibitor of papain but only partially inhibited human kidney cathepsin Bl and did not inhibit the bacterial thiol proteinase, clostripain. Its mean protein concentration in adults sera was 42.5 ± 6.8 mg per dl.     

The inactivation of the cysteinyl exopeptidases cathepsin H and C by affinity-labelling reagents.

An attempt has been made to extend to the cysteinyl exopeptidases cathepsins H and C affinity-labelling approaches shown to be effective with cysteinyl endopeptidases such as cathepsins B and L and the calcium-activated proteinase. This involved the preparation of amino acid and dipeptide derivatives with unblocked N-termini to satisfy the aminopeptidase and dipeptidyl aminopeptidase characteristics of cathepsins H and C respectively. For covalent reactivity, the possibilities examined included diazomethanes (-CHN2), fluoromethanes (-CH2F) and dimethylsulphonium salt [-CH2S+(CH3)2]. A dipeptidylfluoromethane with a free amino group could not be prepared, perhaps due to inherent instability. Cathepsin H was inactivated by 1 microM-H2N-Phe-CH2F (the 'H2N' indicates a free unblocked amino group) (k2 = 1878 M-1.s-1); this reagent was without effect on cathepsins C and B, even at 100-fold this concentration. Analogous selectivity was shown by H2N-Ser(OBzl)-CHN2 and H2N-Phe-CH2S+(CH3)2, members of other classes of covalently binding reagents. For cathepsin C the dipeptide derivatives H2N-Gly-Phe-CHN2 and H2N-Phe-Ala-CH2S+(CH3)2 caused rapid inactivation near 10(-7) M. Higher concentrations inactivated cathepsins H and B, but the rates were slower by two to three orders of magnitude than for cathepsin C.     

Salivary histatin 5 is a potent competitive inhibitor of the cysteine proteinase clostripain

Histatin 5 is a low molecular weight salivary protein which is known to exhibit inhibitory activity against several proteinases, including the cysteine proteinases gingipains. The purpose of this study was to characterize the effect of salivary histatin on the proteolytic activity of the cysteine proteinase clostripain derived from the pathogen Clostridium histolyticum. Using a synthetic nitroanilide substrate, we studied in detail the inhibition of clostripain by histatin 5 and compared the effect of this peptide to that of leupeptin, a known competitive inhibitor of clostripain. It was found that the concentration of histatin 5 required to inhibit 50% of clostripain activity was 23.6+/-1.6 nM. Kinetic analysis revealed that histatin 5 is a competitive inhibitor of clostripain with an inhibition constant (K(i)) of 10 nM. The K(i) for the inhibition of clostripain activity against nitroanilide substrate by leupeptin was found to be 60 nM, significantly higher than that of histatin 5. Thus, histatin 5 inhibits clostripain more effectively than leupeptin and other cysteine protease inhibitors studied here. No significant proteolysis of histatin 5 was observed when histatin 5 was incubated at physiologic concentrations with clostripain. The potent inhibition of clostripain by histatin 5 points towards the possibility that this protein may prevent establishment of clostridial infections and therefore may have significant potential for the treatment of diseases associated with this enzyme.     

Assay of alpha-cysteine proteinase inhibitor in serum or plasma

A new proteinase inhibitor has recently been found in human serum or plasma which specifically inhibits cysteine proteinases such as ficin, papain, bromelain and cathepsin B. However, serum contains alpha 2-macroglobulin which also inhibits these cysteine proteinases and, consequently, interferes with the assay of the new alpha-cysteine proteinase inhibitor. Therefore, assay of the inhibitor in serum has not been established previously. In the present method, the alpha 2-macroglobulin is inactivated by preincubating the serum in methylamine solution at 55 degrees C, while the alpha-cysteine proteinase inhibitor retains its activity. The inhibitory power against cysteine proteinases is found to be due mainly to this protein in human serum. This inhibitor is also found in mammals such as cows, pigs and rats. Vitamin E deficient rats show a very high inhibitor level. Therefore, the present method will enable us to investigate the relation between diseases and the activity of the alpha-cysteine proteinase inhibitor. Also, this method is simple and inexpensive. The necessary amount of serum is only 10 microliter.     

Characterization of the inactive fragment resulting from limited proteolysis of human alpha1-proteinase inhibitor by Crotalus adamanteus proteinase II.

The inactive 50,000-dalton fragment of human plasma alpha1-proteinase inhibitor resulting from limited proteolysis of the inhibitor by Crotalus adamanteus proteinase II has been isolated and partially characterized. The amino acid composition of the inactivated inhibitor indicates the loss of a peptide fragment from the intact inhibitor. Both intact and inactivated inhibitor contain COOH-terminal lysine. However, the NH2 terminus of the intact inhibitor is Glx, whereas that of inactivated inhibitor is methionine. NH2-terminal analysis of the inactive inhibitor fragment revealed the following sequence: -Met-Phe-Leu-Glu-Ala-Ile-Pro-Met-Ser-Ile-Pro-Pro-Gln-Val-Lys-Phe-Asn. The data show that the venom proteinase has inactivated alpha1- proteinase inhibitor by cleavage of a single bond which differs from that reported for trypsin or papain.     

Isolation and characterization of a membrane-bound proteinase from rat liver.

The proteinase previously found in chromatin prepared from a total rat liver homogenate was purified from the rat liver mitochondrial fraction. The membrane-bound enzyme is solubilized in either 0.6% digitonin or 0.5 m phosphate buffer. After a 1330-fold purification, the enzyme appears homogeneous by acrylamide-gel electrophoresis. Sucrose density gradient centrifugation indicated a molecular weight of 22,500, a molecular weight of 23,500 ± 10% has been estimated by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme showed a high substrate specificity. Among several proteins tested, only glucagon, nonhistone chromosomal proteins, and histones are good substrates. A limited proteolysis was found for the very-lysine-rich histone H1, which was split into a high molecular weight fragment (M_r 13,000). The highly phosphorylated histone H1 isolated from regenerating rat liver 24 h after partial hepatectomy exhibited the same susceptibility to the proteinase as H1 from normal liver. Large polypeptides of a nonhistone chromosomal protein fraction were degraded more rapidly than the small ones. N-Acetyl-l-tyrosine ethyl ester was used with alcohol dehydrogenase and NAD in a coupled enzyme assay for the proteinase. The apparent Michaelis constant for the hydrolysis of N-acetyl-l-tyrosine ethyl ester is 5.0 × 10^?3m. The proteinase has catalytic properties simlar to trypsin and chymotrypsin. The pH optimum was around 8, soybean trypsin inhibitor depressed the enzymatic activity, and the serine modifying reagents diisopropyl phosphofluoridate and phenylmethanesulfonyl fluoride inactivated the enzyme. The affinity reagent for chymotrypsin-like active sites, l-1-tosylamido-2-phenylethyl chloromethyl ketone, inactivated the proteinase.     

L-trans-Epoxysuccinyl-leucylamido(4-guanidino)butane (E-64) and its analogues as inhibitors of cysteine proteinases including cathepsins B, H and L.

1. L-trans-Epoxysuccinyl-leucylamido(4-guanidino)butane (E-64) at a concentration of 0.5 mM had no effect on the serine proteinases plasma kallikrein and leucocyte elastase or the metalloproteinases thermolysin and clostridial collagenase. In contrast, 10 muM-E-64 rapidly inactivated the cysteine proteinases cathepsins B, H and L and papain (t0.5 = 0.1-17.3s). The streptococcal cysteine proteinase reacted much more slowly, and there was no irreversible inactivation of clostripain. The cysteine-dependent exopeptidase dipeptidyl peptidase I was very slowly inactivated by E-64. 2. the active-site-directed nature of the interaction of cathepsin B and papain with E-64 was established by protection of the enzyme in the presence of the reversible competitive inhibitor leupeptin and by the stereospecificity for inhibition by the L as opposed to the D compound. 3. It was shown that the rapid stoichiometric reaction of the cysteine proteinases related to papain can be used to determine the operational molarity of solutions of the enzymes and thus to calibrate rate assays. 4. The apparent second-order rate constants for the inactivation of human cathepsins B and H and rat cathepsin L by a series of structural analogues of E-64 are reported, and compared with those for some other active-site-directed inhibitors of cysteine proteinases. 5. L-trans-Epoxysuccinyl-leucylamido(3-methyl)butane (Ep-475) was found to inhibit cathepsins B and L more rapidly than E-64. 6. Fumaryl-leucylamido(3-methyl)butane (Dc-11) was 100-fold less reactive than the corresponding epoxide, but was nevertheless about as effective as iodoacetate.     

Amino acid sequence of the Bb fragment from complement Factor B. Sequence of the major cyanogen bromide-cleavage peptide (CB-II) and completion of the sequence of the Bb fragment.

The amino acid sequence of peptide CB-II, the major product (mol.wt. 30 000) of CNBr cleavage of fragment Bb from human complement Factor B, is given. The sequence was obtained from peptides derived by trypsin cleavage of peptide CB-II and clostripain digestion of fragment Bb. Cleavage of two Asn-Gly bonds in peptide CB-II was also found useful. These results, along with those presented in the preceding paper [Gagnon & Christie (1983) Biochem. J. 209, 51-60], yield the complete sequence of the 505 amino acid residues of fragment Bb. The C-terminal half of the molecule shows strong homology of sequence with serine proteinases. Factor B has a catalytic chain (fragment Bb) with a molecular weight twice that of proteinases previously described, suggesting that it is a novel type of serine proteinase, probably with a different activation mechanism.     

The effect of mixed-function oxidation of enzymes on their susceptibility to degradation by a nonlysosomal cysteine proteinase

Mixed-function oxidation of Escherichia coli glutamine synthetase by ascorbate, oxygen, and iron has previously been shown to cause inactivation of the enzyme and enhanced susceptibility to proteolytic attack by a variety of proteases. One of these proteases, from rat liver, is a high molecular weight cysteine proteinase which does not degrade native glutamine synthetase at neutral pH. Although inactive, the oxidized glutamine synthetase preparations used in this study were only partially degraded by this proteinase. Some of the subunits were degraded to acid soluble products with no detectable intermediates; the remaining subunits had not become susceptible to proteolytic attack during the limited exposure to the ascorbate mixed-function oxidation system. Several mammalian enzymes which are known to be inactivated by mixed-function oxidation were tested as substrates for the proteinase. Native rabbit muscle enolase and pyruvate kinase were resistant to degradation, but their oxidatively inactivated forms were degraded. Oxidized phosphoglycerate kinase and creatine kinase were also preferentially degraded. Moreover, trypsin degraded oxidized preparations of all of these enzymes faster than control preparations. Oxidative inactivation of superoxide dismutase by hydrogen peroxide caused a slight increase in susceptibility to proteolytic attack, but the enzyme was still relatively resistant to degradation both by the cysteine proteinase and by trypsin. Although oxidation conditions may not have been optimal for demonstrating enhanced proteolytic susceptibility, the results do indicate that mixed-function oxidation can render some mammalian enzymes, as well as bacterial glutamine synthetase, susceptible to degradation. Mixed-function oxidation of these proteins may be a mechanism of marking them for intracellular turnover.     

Biochemical properties of purified cathepsin B from Schistosoma mansoni

A previously described “major acidic proteinase” of adult Schistosoma mansoni, believed to play a key role in the parasite's metabolism, has been identified as a cathepsin B (Sm31). Purified Sm cathepsin B was not recognized by anti-Sm32 or anticathepsin L antibodies. The enzyme hydrolyzes the synthetic protease substrates Z-Arg-Arg-AMC and Z-Phe-Arg-AMC as well as protein substrates. Its pH optimum is 3.0 with serum albumin, 4.0–5.0 with globin and 5.5–6.0 with the synthetic substrates. The enzyme was inactivated by cysteine proteinase inhibitors. Its activity against protein substrates would support the hypothesis that it plays a role in schistosome nutrition.     

A CLN2-related and thermostable serine-carboxyl proteinase, kumamolysin: cloning, expression, and identification of catalytic serine residue

The gene encoding kumamolysin, a thermostable pepstatin-insensitive carboxyl proteinase, was cloned and expressed. (i) Kumamolysin was synthesized as a large precursor consisting of two regions: amino-terminal prepro (188 amino acids) and mature proteins (384 amino acids). (ii) The deduced amino acid sequence of the mature region exhibited high similarity to those of such bacterial pepstatin-insensitive enzymes as Pseudomonas carboxyl proteinase (PSCP; EC 3.4.23.37, identity = 37%), Xanthomonas carboxyl proteinase (XCP; EC 3.4.23.33, identity = 36%), and human CLN2 gene product (identity = 36%), which is related to a fatal neurodegenerative disease. (iii) The presumed catalytic triad, Glu78, Asp82, Ser278 [three-dimensional structure of PSCP: Wlodawer, A. et al. (2001) Nature Struct. Biol., 8, 442-446], was found to be conserved in the amino acid sequence of kumamolysin. (iv) Kumamolysin was inactivated by such aldehyde-type inhibitors as Ac-Ile-Pro-Phe-CHO (K(i) = 0.7 0.14 microM). In PSCP, it has been clarified that these inhibitors form a hemiacetal linkage with the catalytic serine residue and inactivate the enzyme. (v) Mutational analysis of the Ser278 residue revealed that the mutant lost both auto-processing activity and proteolytic activity. These results strongly suggest that kumamolysin has a unique catalytic triad consisting of Glu78, Asp82, and Ser278 residues, as previously observed for PSCP.     

Isolation and properties of serine proteinase from Aspergillus oryzae

A serine proteinase having an activity optimum at pH 6.7-8.2 has been isolated from amylorisine P-10x (a mixture of Aspergillus oryzae enzymes) by chromatography on DEAE-Sephadex A-50 and bacitracin Sepharose 4B. The proteinase is fully inactivated by phenylmethylsulfonylfluoride and diisopropylfluorophosphonate, the specific inhibitors of the enzyme, and has a pI at pH 7.5. The molecular mass of serine proteinase is 30000 Da; its amino acid composition appears as: Met2, Asp33, Thr18, Ser29, Glu21, Pro9, Glu32, Ala38, Val24, Ile16, Leu15, Tyr8, Phe8, His8, Lys18, Arg4, Trp6. The N-terminal sequence of the serine proteinase: Gly-Leu-Thr-Thr-Gln-Lys-Ser-Ala-Pro-Trp-Gly-Leu-Gly-Ser-Ile-Ser-Xaa-Lys- Gly-Gln-Gln-Ser-Thr-Asp-Tyr-Ile-Tyr, which coincides practically completely with the corresponding sequence of alkaline proteinase of A. oryzae, ATCC20386, has been determined. Similar to subtilisin, the enzyme catalyzes the condensation of leucine and alanine p-nitroanilides with N-benzyloxycarbonyl-alanyl-alanine and glycyl-alanine methyl esters.     

Isolation, characterization and localization of the proteinase B inhibitor IB3 from Saccharomyces carlsbergensis.

A heat-stable polypeptide has been detected in Saccharomyces carlsbergensis which inhibits specifically proteinase B from yeast. This proteinase B inhibitor IB3 differs substantially in chemical, physical and antigenic properties from the earlier described proteinase B inhibitors IB1 and IB2 from yeast. The inhibitor IB3 has been purified from S. carlsbergensis and appears to be homogeneous by disc gel electrophoresis and sodium dodecyl sulfate gel electrophoresis. The molecular weight has been estimated at 11 500, with no evidence for the existence of subunits. The amino acid analysis shows the absence of tryptophan. No compounds other than amino acids could be detected. The isoelectric point is 4.6. The inhibitor is not affected by incubation with proteinase B but is inactivated by proteinase A and carboxypeptidase Y from yeast and by trypsin from bovine pancreas. The proteinase B inhibitor association constant was calculated to be 3.3 x 10(9) M-1 and the enzyme inhibitor complex is stable at 25 degrees C in the pH range 5--10. The inhibitor does not exhibit immunological cross-reactivity with IB1 and IB2. After centrifugal fractionation at 40 000 x g of a metabolic lysate from spheroplasts the inhibitor was found to be localized in the supernatant, i.e. the extravacuolar soluble fraction.     

Calcium protects DNase I from proteinase K: a new method for the removal of contaminating RNase from DNase I

DNase I and proteinase K are two enzymes commonly used in the purification of highly polymerized RNA. In the presence of EDTA DNase I is rapidly inactivated by proteinase K while in 10 mm Ca²⁺ DNase is totally immune to proteinase K inactivation even at protease concentrations of up to 1 mg/ml. RNase A, a common contaminant of “RNase-free” DNase was inactivated by proteinase K in the presence or absence of Ca²⁺. Treatment of DNase I with proteinase K in the presence of Ca²⁺ selectively removed RNase A activity as judged by rRNA and poly(A⁺ RNA ribosomal RNA degradation monitored by sucrose gradient centrifugation. These results suggest that (i) DNase A and proteinase K can be used together in the presence of Ca²⁺ to obtain better digestion of nucleoprotein complexes, and (ii) proteinase K treatment of Ca²⁺ DNase can be used to selectively remove contaminating RNase.     

The properties of peptidyl diazoethanes and chloroethanes as protease inactivators

Earlier work has demonstrated the irreversible inactivation of serine and cysteine proteinases by peptides with a C-terminal chloromethyl ketone group. With a C-terminal diazomethyl ketone, on the other hand, peptides become reagents specific for cysteine proteinases. We have now synthesized and examined the properties of reagents with an additional methyl side chain near the reactive grouping with the goal of diminishing side reactions in a cellular environment. Derivatives of neutral amino acids as well as of lysine and arginine have been prepared. The chloroethyl ketones are about 60% less reactive to chemical nucleophiles than the chloromethyl ketones. However, the susceptibilities of the proteases examined varied remarkably. Cathepsins B and L of the papain family of cysteine proteinases were much less susceptible (about 2 orders of magnitude less) to both peptidyl diazoethyl and chloroethyl ketones. In marked contrast, clostripain, a cysteine proteinase of a separate family was decisively more susceptible to chloroethyl ketones. The serine proteinases showed a drop in susceptibility to the chloroethyl ketones generally, and this was similar to the drop in chemical reactivity in proceeding from the chloromethyl to the chloroethyl ketone.     

Effects of a membrane-bound trypsin-like proteinase and seminal proteinase inhibitors on the bicarbonate-sensitive adenylate cyclase in porcine sperm plasma membranes

Plasma membranes were purified from flagella of porcine cauda epididymal sperm and proteolytic regulation of bicarbonate-sensitive adenylate cyclase was studied. It was found that the epididymal sperm plasma membrane contained a trypsin-like proteinase which inactivated adenylate cyclase. Bicarbonate activates adenylate cyclase as reported previously, but, at the same time, the anions enhance the inactivation of the enzyme by the membrane-bound trypsin-like proteinase. This phenomenon is not due to the direct activation of the proteinase, but closely related to the activation of adenylate cyclase by bicarbonate. It was also found that seminal proteinase inhibitors blocked the inactivation of adenylate cyclase and maintained the bicarbonate activation of the enzyme at high level. Actually, bicarbonate keeps adenylate cyclase fully active in ejaculated sperm, because membrane-bound proteinase is completely inhibited by the seminal proteinase inhibitors. These results suggest that the interactions between membrane-bound proteinase and seminal proteinase inhibitor are involved in the regulation of the bicarbonate-sensitive adenylate cyclase system.