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PubMed1991

Structure, chromosomal assignment, and deduced amino acid sequence of a human gene for mast cell chymase.

A gene encoding human chymase was cloned and sequenced. The protein-coding exons reveal a preproenzyme with a 19-amino acid signal peptide, an acidic 2-amino acid propeptide, and a 226-amino acid catalytic domain. The mature enzyme is predicted to be cationic (net charge of +13) and to be modified by N-glycosylation at two sites. The amino acid sequence is identical to the 35 residues of NH2-terminal amino acid sequence reported for human skin chymase and is identical to 29 of 31 residues of NH2-terminal and internal amino acid sequence reported for human heart chymase. The full predicted sequence of the catalytic domain reveals a high level of sequence identity to dog mast cell chymase (83%) and a lower level of identity to the sequences of rodent chymases (58-62%). In the phase and placement of introns, the organization of this human chymase gene is similar to that of several other granule-associated leukocyte serine proteases, including rat chymase II, lymphocyte granzymes, and neutrophil cathespin G and elastase. However, the gene organization differs from that of mast cell tryptase, providing additional evidence that the major mast cell serine proteases are separated by substantial evolutionary distance. Amplification of chymase gene-specific fragments from hamster/human hybrid cell line DNA suggests localization of the chymase gene to human chromosome 14. High stringency hybridization of chymase DNA to a human genomic DNA blot suggests the possibility of more than one human chymase gene. Evidence that the chymase gene is expressed in human tissues was obtained by the amplification of chymase-specific DNA from skin and placental cDNA libraries.

Amino Acid Sequence↗

PubMed1990

Mast cell chymase potentiates histamine-induced wheal formation in the skin of ragweed-allergic dogs.

Skin mast cells release the neutral protease chymase along with histamine during degranulation. To test the hypothesis that chymase modulates histamine-induced plasma extravasation, we measured wheal formation following intradermal injection of purified mast cell chymase and histamine into the skin of ragweed-allergic dogs. We found that chymase greatly augments histamine-induced wheal formation. The magnitude of the potentiating effect increases with increasing doses of chymase and becomes maximal approximately 30 min after administration. Injection of chymase without histamine does not evoke wheal formation. The chymase potentiation of histamine-induced skin responses is prevented completely by pretreatment with the H1-receptor antagonist pyrilamine, and is prevented by inactivation of chymase with soybean trypsin inhibitor, suggesting that both histamine and preserved catalytic activity are required for the effects of chymase. To examine the effects of histamine and chymase released in situ in further experiments, we measured wheal size following local degranulation of mast cells by intradermal injection of ragweed antigen or compound 48/80. We found that pretreatment with either soybean trypsin inhibitor or pyrilamine markedly reduces ragweed antigen- or 48/80-induced wheal formation, supporting the results obtained by injection of exogenous chymase and histamine. These findings suggest a novel and important proinflammatory role for chymase in modulating the effects of histamine on vascular permeability during mast cell activation.

Allergens↗

PubMed1992

Mast cell proteoglycans modulate the secretagogue, proteoglycanase, and amidolytic activities of dog mast cell chymase.

Chymase, a potent secretagogue for airway gland serous cells, is stored in secretory granules and released from mast cells together with proteoglycans. To investigate the hypothesis tha tproteoglycans modulate chymase-induced effects, we studied the influence of proteoglycans purified from dog mastocytoma cells on chymase-induced secretion from cultured bovine airway gland serous cells. Heparin proteoglycans reduced the chymase-induced secretory response, whereas glycosaminoglycans and chondroitin sulfate proteoglycans had less of an effect. Chymase released together with proteoglycans from activated mast cells caused secretion comparable to that caused by purified chymase reconstituted with purified proteoglycans. Despite partial inhibition by exocytosed proteoglycans, the secretagogue activity of chymase remains substantial compared to that of histamine. However, proteoglycans virtually abolished chymase-induced degradation of the products of serous cell secretion. Although the secretagogue and proteoglycanase activities of chymase are inhibited by most classes of mast cell granule-associated glycans, the amidolytic activity of chymase toward tripeptide 4-nitroanilide substrates is augmented. These findings suggest that mast cell proteoglycans modulate the secretagogue, proteoglycanase, and peptidase activity of chymase, and the results predict that the extent of this modulation in vivo depends on the nature of the proteoglycans with which chymase is released from mast cells.

Animals↗

PubMed1990

Cleavage of a rat serosal mast cell membrane component during degranulation mediated by chymase, a secretory granule protease.

Exogenous addition of purified chymase, a rat serosal mast cell (RSMC) chymotryptic enzyme, results in RSMC degranulation at 37 degrees, but not at 1 degree. Chymase can cause an active site-dependent inducing event at 1 degree such that RSMC degranulation occurs if the cells are later incubated at 37 degrees. RSMC exposed to chymase or other stimuli were surface radiolabelled using 125I and Iodo-Gen, solubilized with 1% Nonidet-40, and the resulting 25,000 g supernatants analysed by SDS-PAGE and autoradiography. A 125I-labelled RSMC membrane protein of approximate 90,000 MW decreased upon exposure to either chymase or alpha-chymotrypsin (alpha-CT) for 5 min at 37 degrees or to chymase for 60 min at 1 degree. Exposure of RSMC to the secretagogues ionophore A23187, compound 48/80, and anti-IgE for 5 min at 37 degrees resulted in beta-hexosaminidase (a secretory granule enzyme) release, but did not cause a detectable change in the 90,000 MW surface-labelled protein. Lima bean trypsin inhibitor, which inhibits both the esterase and RSMC degranulation activities of chymase and alpha-CT, prevented the disappearance of the 125I-labelled 90,000 MW band when added with chymase or alpha-CT. Exposure of RSMC to chymase at 1 degree for 0-10 min, prior to addition of LBTI, led to a progressive disappearance of the 90,000 MW band, which corresponded to the kinetics of priming for subsequent RSMC degranulation at 37 degrees. When RSMC were exposed to trypsin (2.5 micrograms/ml) for 0-120 min at 1 degree, a progressive disappearance of the 90,000 MW band occurred, in association with a loss of sensitivity to subsequent activation by chymase at 37 degrees. The disappearance of the 90,000 MW determinant in association with chymase-mediated priming for degranulation and the inability of chymase to mediate degranulation of trypsin-treated RSMC, which lack this membrane protein, suggests that it is involved in chymase-mediated RSMC degranulation.

Animals↗

PubMed1989

Modulation of chymase-mediated rat serosal mast cell degranulation by trypsin or diisopropyl fluorophosphate.

Exposure of rat serosal mast cells (RSMC) to chymase, an endogenous secretory granule serine protease, at 37 degrees results in exocytosis, as determined by beta-hexosaminidase release. As the number of RSMC is increased with a set amount of chymase, the net percentage beta-hexosaminidase release decreases linearly, implying a finite set of cellular interactions per chymase unit. Pretreatment of RSMC with trypsin at 37 degrees renders them refractory to subsequent exocytosis mediated by chymase in a dose- and time-dependent fashion, with complete refractiveness occurring by 15 min at 37 degrees with 2.5 micrograms trypsin/ml. Anti-IgE-mediated coupled activation-secretion of RSMC is not affected by the same trypsin pretreatment. When RSMC are pretreated with trypsin (2.5 micrograms/ml) for 0-120 min at 1 degree a progressive loss of sensitivity to activation by chymase at 37 degrees occurs. RSMC susceptibility to chymase-mediated degranulation after trypsin pretreatment can be partially regenerated by culturing the RSMC for about 24 hr in medium at 37 degrees. These findings suggest that a trypsin-sensitive constituent, possibly a receptor or substrate, is necessary for the functional interaction of chymase with RSMC. When added with diisopropyl fluorophosphate (DFP), chymase does not induce RSMC degranulation at 37 degrees. However, if the DFP is removed before addition of chymase at 37 degrees or is added after the chymase-priming event occurs at 1 degree, subsequent degranulation at 37 degrees is not inhibited. Thus, the induction and not the secretion phase is DFP-inhibitable in chymase-induced activation-secretion. In addition, the priming but not the exocytosis phase of chymase-initiated RSMC activation-secretion, which is not dependent on temperature and calcium ion concentration, involves a cellular trypsin-sensitive protein.

Animals↗

PubMed1992

Molecular cloning and characterization of mouse mast cell chymases.

Mouse mast cell chymases are granule-associated serine proteinases with chymotrypsin-like substrate specificities. cDNAs for two new chymases were isolated from a cDNA library constructed using mRNA from ABFTL-6 mouse mast cells by screening with a rat mast cell proteinase cDNA. The deduced amino acid sequence of mouse chymase 1 consists of a 226 amino acid catalytic portion and a 21 amino acid preprosequence. Chymase 1 is unusual in that an Asn occurs in the substrate binding pocket, a feature that has not been observed in any other serine proteinase. Also, chymase 1 is expected to have a large positive charge (+13) at physiological pH. A partial cDNA for chymase 2 encodes 177 residues of the carboxy terminal portion of a second proteinase distinct from chymase 1. Chymase 2 cDNA contains a highly conserved intron/exon junction, a high positive charge (+17) and a novel, second potential N-glycosylation site. Transcripts for both chymases are found in ABFTL-6 mast cells, but only chymase 2 mRNA is in mouse connective tissue mast cells. These data suggest that these chymases have distinct enzymatic properties and tissue-specific patterns of gene expression.

Amino Acid Sequence↗

PubMed1986

Rat serosal mast cell degranulation mediated by chymase, an endogenous secretory granule protease: active site-dependent initiation at 1 degree C.

Exposure at 37 degrees C of rat serosal mast cells (RSMC) to chymase, an endogenous secretory granule serine protease, results in exocytosis as determined by the release of another secretory granule enzyme, beta-hexosaminidase. Chymase-mediated RSMC degranulation does not occur at 1 degree C; however, exposure of RSMC to chymase at 1 degree C followed by the removal of buffer and the resuspension of the cells in buffer alone at 37 degrees C results in exocytosis equivalent to that obtained by direct exposure of RSMC to chymase at 37 degrees C. Maximal chymase-mediated RSMC degranulation at 37 degrees C is Ca2+-dependent and Mg2+-independent. The dose-dependent degranulation-inducing interaction of chymase and alpha-chymotrypsin with RSMC at 1 degree C is Ca2+-independent, whereas subsequent exocytosis at 37 degrees C in new buffer without added enzyme still requires Ca2+. Specific binding of 125I-labeled alpha-chymotrypsin to RSMC does not occur at 1 degree C, implying that the inducing action of chymase is not a simple ligand-receptor binding. The enzyme inhibitors diisopropyl fluorophosphate and lima bean trypsin inhibitor inhibit subsequent exocytosis at 37 degrees C only if they are added within the first 10 min of the interaction of RSMC and chymase at 1 degree C, implying that an active site-dependent inducing event occurs between RSMC and chymase at 1 degree C. Thus, chymase-induced coupled activation-secretion can be divided into a cation- and temperature-independent initiation phase, which is dependent on the active site of exogenously added chymase and a subsequent temperature-dependent and calcium-augmented cellular secretion phase.

Animals↗

PubMed1985

Pharmacological modulation of activation-secretion of rat serosal mast cells by chymase, an endogenous secretory granule protease.

The action of pharmacologic agents on chymase-induced exocytosis of beta-hexosaminidase and arachidonic acid (AA) metabolism by rat serosal mast cells (RSMC) was determined and compared with their effects on anti-IgE induced activation. Indomethacin (INDO) (less than or equal to 10 microM), a cyclooxygenase inhibitor, did not affect chymase- or anti-IgE-mediated exocytosis, while completely inhibiting prostaglandin D2 (PGD2) release at 1.25 microM. Theophylline (THEO), mepacrine, 3-amino-1-[m-(trifluoromethyl)-phenyl]-2-pyrazoline (BW755C), and diethylcarbamazine (DEC), inhibitors of adenosine binding and phosphodiesterases, phospholipases, AA metabolism, and vesicular transport as well as leukotriene A4 formation, respectively, inhibited exocytosis with ID50 values of 3.4, 0.22, 3.4 and 1.9 mM for chymase and 2.4, 0.17, 2.8 and 5.2 mM for anti-IgE. These agents inhibited net PGD2 release with ID50 values of 2.1, 0.04, less than 0.05, and 1.5 mM for chymase and of 0.5, 0.1, less than 0.05, and 4 mM for anti-IgE. 5,6-Dehydroarachidonic acid (DHA) and arachidonyl hydroxylamine (AH), 5-lipoxygenase inhibitors, did not affect chymase-mediated exocytosis; anti-IgE-mediated exocytosis was not altered by AH but was suppressed by DHA (ID50 = 20 microM). Nordihydroguaiaretic acid (NDGA), an antioxidant, inhibited chymase-mediated exocytosis dose-dependently (ID50 less than or equal to 13.3 microM) while decreasing anti-IgE-mediated exocytosis by only 30% at 2.5-20 microM; net PGD2 release induced by both stimuli was inhibited dose-dependently. 2',5'-Dideoxyadenosine (DDA) and 1,6-di(0-(carbamoyl)cyclohexanone oxime)hexane (RHC 80267) and inhibitors of adenylate cyclase and of di-triglyceride lipases, respectively, had little effect on exocytosis induced by chymase but inhibited that induced by anti-IgE with ID50 values of 0.4 mM and 37 microM, respectively. With DDA the inhibition of net PGD2 release occurred with anti-IgE but not chymase, whereas RHC 80267 inhibited both chymase and anti-IgE-mediated PGD2 release. Differential inhibition of activation-secretion suggests either that chymase provides a step inhibited in IgE-mediated exocytosis by DDA, RHC 80267 and DHA, or that the activating pathway initiated by chymase is distinct.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

PubMed1992

Distribution of chymase-containing mast cells in human bronchi.

Mast cell chymase stimulates secretion from cultured airway gland serous cells and hydrolyzes bronchoactive peptides in vitro. To explore the likelihood of these interactions occurring in situ, we examined the distribution and concentration of chymase-containing mast cells near glands and smooth muscle of major human bronchi from eight individuals without known airway disease. Total airway mast cells and the subset of mast cells containing chymase were detected by staining for methylene blue metachromasia and chloroacetate esterase activity, respectively. The percentage of chymase-containing mast cells was found to differ strikingly among bronchial tissue compartments. Near glands, for example, the concentration of chymase-positive mast cells (640 +/- 120 cells/mm3) was 73 +/- 9% that of total mast cells (910 +/- 130 cells/mm3), whereas in smooth muscle the concentration of chymase-positive mast cells (450 +/- 200 cells/mm3) was only 14 +/- 4% that of total mast cells (2920 +/- 620 cells/mm3). Of all chymase-containing mast cells in the airway subepithelium, 30 +/- 4% were located within 20 microns of submucosal glands. Although the percentage of chymase-containing cells varied, the absolute concentration of chymase-containing mast cells was similar in all compartments. These results reveal a differential distribution of mast cell subpopulations in human airway and suggest that mast cells containing chymase are near gland and smooth muscle targets.

Bronchi↗

PubMed1991

Cloning of the gene and cDNA for human heart chymase.

We have recently identified and characterized a chymotrypsin-like serine proteinase in human heart (human heart chymase) that is the most catalytically efficient enzyme described, thus far, for the cleavage of angiotensin I to yield angiotensin II and the dipeptide His-Leu. Compared to other chymases, this enzyme also has an unusually high degree of specificity for the substrate angiotensin I. We report here the molecular cloning and nucleotide sequence of the gene and cDNA encoding human heart chymase, and determination of its entire deduced amino acid sequence. These data indicate that human heart chymase is highly homologous to other members of the chymase subfamily of chymotrypsin-like proteinases and, most likely, all evolved from a common ancestral gene. Potential regulatory elements found in the 5'-untranslated region of other chymases are also found in the human heart chymase gene. However, this gene lacks mast cell-specific sequences found in the 5'- and 3'-untranslated regions of the rat chymase II gene. In addition, human heart chymase contains clusters of unique amino acid sequences located at key positions likely involved in substrate binding, which may contribute to its high substrate specificity. These contrasting features of the human heart chymase gene and cDNA, and the potential determinants of its primary structure that underlie its unique functional characteristics are considered.

Amino Acid Sequence↗

PubMed1989

Mast cell chymase. A potent secretagogue for airway gland serous cells.

Submucosal glands are the major sources of airway secretions in most mammals. Mast cells are abundant in the environment of airway submucosal glands and are rich sources of secreted proteases. To investigate the hypothesis that mast cell proteases stimulate airway gland secretion, we studied the ability of the two major mast cell granule proteases, chymase and tryptase, to cause secretion of 35S-labeled macromolecules from a line of cultured bovine airway gland serous cells. Mast cell chymase and tryptase were purified from dog mastocytoma cells. Chymase markedly stimulated serous cell secretion in a concentration-dependent fashion with a threshold of 10(-10) M, whereas tryptase had no effect. The response to 10(-8) M chymase (1530 +/- 80% over base line) was approximately 10-fold higher than that evoked by other agonists such as histamine and isoproterenol. The predominant 35S-labeled macromolecule released by chymase was chondroitin sulfate proteoglycan, the glycoconjugate present in serous cell secretory granules. The response to chymase was non-cytotoxic and was blocked by active site inhibitors of chymase (soybean trypsin inhibitor and chymostatin) and by inhibitors of cellular energy metabolism (azide,2,4-dinitrophenol, dicumarol). Supernatant obtained by degranulation of mastocytoma cells caused a secretory response of comparable magnitude to that caused by chymase. These findings demonstrate that chymase, but not tryptase, is a potent secretagogue for airway gland serous cells, and they suggest a possible role for chymase-containing mast cells in the pathogenesis of airway hypersecretion.

Animals↗

PubMed1989

Reaction of human skin chymotrypsin-like proteinase chymase with plasma proteinase inhibitors.

The ability of plasma proteinase inhibitors to inactivate human chymase, a chymotrypsin-like proteinase stored within mast cell secretory granules, was investigated. Incubation with plasma resulted in over 80% inhibition of chymase hydrolytic activity for small substrates, suggesting that inhibitors other than alpha 2-macroglobulin were primarily responsible for chymase inactivation. Depletion of specific inhibitors from plasma by immunoadsorption using antisera against individual inhibitors established that alpha 1-antichymotrypsin (alpha 1-AC) and alpha 1-proteinase inhibitor (alpha 1-PI) were responsible for the inactivation. Characterization of the reaction between chymase and each inhibitor demonstrated in both cases the presence of two concurrent reactions proceeding at fixed relative rates. One reaction, which led to inhibitor inactivation, was about 3.5 and 4.0-fold faster than the other, which led to chymase inactivation. This was demonstrated in linear titrations of proteinase activity which exhibited endpoint stoichiometries of 4.5 (alpha 1-AC) and 5.0 (alpha 1-PI) instead of unity, and SDS gels of reaction products which exhibited a banding pattern indicative of both an SDS-stable proteinase-inhibitor complex and two lower Mr inhibitor degradation products which appear to have formed by hydrolysis within the reactive loop of each inhibitor. At inhibitor concentrations approaching those in plasma where inhibitor to chymase concentration ratios were in far excess of 4.5 and 5.0, the rate of chymase inactivation by both serpin inhibitors appeared to follow pseudo-first order kinetics. The "apparent" second order rate constants of inactivation determined from these data were about 3000-fold lower than the rate constants reported for human neutrophil cathepsin G and elastase with alpha 1-AC and alpha 1-PI, respectively. This suggests that chymase would be inhibited about 650-fold more slowly than these proteinases when released into plasma. These studies demonstrate that although chymase is inactivated by serpin inhibitors of plasma, both inhibitors are better substrates for the proteinase than they are inhibitors. This finding along with the slow rates of inactivation indicates that regulation of human chymase activity may not be a primary function of plasma.

Chymases↗

PubMed1987

Quantitation of histamine, tryptase, and chymase in dispersed human T and TC mast cells.

Levels of histamine, chymase, and tryptase were assessed in preparations of dispersed human TC (tryptase+, chymase+) mast cells obtained from foreskin and of dispersed human T (tryptase+, chymase-) mast cells obtained from lung. Consistent with previous immunohistochemical results, extracts of T mast cells, the predominant mast cell type in lung (93% T and 7% TC mast cells), were deficient in human chymase (less than 0.3 microgram and 0.04 U/10(6) mast cells) but not tryptase (10.8 micrograms and 0.3 U/10(6) mast cells) by corresponding immunologic and enzymatic (suc-L-ala-ala-pro-phe-p-nitroanilide in the presence of aprotinin and tosyl-L-gly-pro-lys-p-nitroanilide in the presence of soybean trypsin inhibitor, respectively) assays. The minor presence of chymase activity in lung could be accounted for by the minor presence of lung TC mast cells. Extracts of TC mast cells, the predominant mast cell type (1% T and 99% TC mast cells) in foreskin, contained both proteases. However, TC mast cells from adult foreskin contained eightfold to 10-fold higher levels of chymase (4.5 micrograms and 1.01 U/10(6) mast cells) and twofold to threefold higher levels of tryptase (11.5 micrograms and 0.27 U/10(6) mast cells) than did TC mast cells from newborn foreskin (less than 0.6 microgram and 0.09 U of chymase and 35 micrograms and 0.62 U of tryptase/10(6) mast cells). In contrast, histamine levels were not significantly different in adult foreskin TC (1.9 microgram/10(6) mast cells), newborn foreskin TC (1.6 microgram/10(6) mast cells), and adult lung T (1.5 microgram/10(6) mast cells) mast cells. The relative ratio of each mediator in newborn foreskin mast cells to that in adult foreskin mast cells is highest for histamine, followed by tryptase and then chymase. Tryptase from TC and T mast cells had identical subunit compositions by Western blot analysis and similar apparent specific activities. This study extends the previously reported immunohistochemical distinction between human T and TC mast cells in tissue sections by direct quantitation of chymase and tryptase in dispersed preparations of T and TC mast cells.

Adult↗

PubMed1977

Preparative purification of the rat mast cell chymase: characterization and interaction with granule components.

The rat mast cell granule chymotrypsinlike enzyme was purified to homogeneity from 1 M NaCl solubilized membrane and granule-rich fractions of concentrated rat peritoneal mast cells by a preparative technique utilizing chromatography on Dowex 1, filtration on Sephadex G-75, and affinity chromatography with D-tryptophan methyl ester. Acid disk gel electrophoresis of the purified chymase disclosed a single stained band with activity being eluted from a replicate sliced gel in the same region. SDS-polyacrylamide gel electrophoresis of purified protein gave a single stained band that did not change in position with reduction and alkylation. Mast cell chymase is thus a cationic protein of 25,000 mol wt composed of a single polypeptide chain. The apparent K(m) of the chymase for BTEE was 1.5 x 10(-3) M and the V(max) was 67.8 mumol/min per mg. The enzyme was inhibited by TPCK and not by TLCK. The chymase complexed with native macromolecular rat mast cell heparin in molar ratios of 12:1 and 16:1, and complete heparin uptake occurred at a 40:1 ratio of chymase to heparin. Chymase activity was partially masked by combination with heparin in the isolated granule or experimental chymase-heparin complex, and soluble purified chymase was inhibited by concentrations of 5-HT comparable to those present in mast cells. It is therefore possible that the active site of chymase in the mast cell granule is largely masked by the combined effects of macromolecular heparin and 5-HT.

Animals↗

PubMed1990

Quantitative enzyme-histochemical analysis of tryptase- and chymase-containing mast cells in psoriatic skin.

Tryptase-containing mast cells have recently been found to be increased in the upper dermis of psoriatic lesions. In the present study, the distribution of chymase- and tryptase-containing mast cells was morphometrically analysed at different dermal levels of lesional and non-lesional psoriatic skin (12 patients) as well as normal human skin. Mast cell tryptase was identified enzyme-histochemically, using Z-Gly-Pro-Arg-MNA as the substrate. For demonstrating mast cell chymase, a simple and specific enzyme-histochemical staining method was developed, using Suc-Val-Pro-Phe-MNA as the substrate. All mast cells positive for chymase were also positive for tryptase and Giemsa stain. Although the number of tryptase-positive mast cells was slightly increased throughout the dermis of lesional psoriatic skin, this increase was most pronounced in the upper dermis immediately beneath, and in close contact with, the epidermis. In contrast, the number of chymase-positive mast cells was clearly decreased in the upper dermis of psoriatic lesions, but not in the deeper dermis, as compared with non-lesional psoriatic skin. In addition, all chymase-positive mast cells observed in the upper dermis were very weakly stained when compared with those in the deeper dermis. No differences were found between non-lesional psoriatic skin and normal skin in which the number of mast cells containing chymase was 72-73% of the number containing tryptase. The present results suggest that T mast cells particularly, containing tryptase but no chymase, proliferate in psoriatic lesions, and that the increase in tryptase activity and the decrease in chymase activity in the upper dermis may lead to an imbalance in the biochemical regulatory systems.

Adolescent↗

PubMed1990

Dog mast cell chymase: molecular cloning and characterization.

We cloned and characterized a cDNA coding for the complete amino acid sequence of dog mast cell chymase. The cDNA was identified by screening a dog mastocytoma cDNA library with an oligonucleotide probe based on the amino acid sequence of a fragment of dog mastocytoma chymase. The deduced amino acid sequence reveals a putative 21-residue prepropeptide followed by a catalytic domain of 228 residues. The primary structure of the preproenzyme shares features with rat mucosal mast cell chymase (RMCP II), several lymphocyte-associated proteases, and neutrophil cathepsin G. The common characteristics include an apparent activation peptide terminating in glutamic acid, strict conservation of an octapeptide (residues 9-16) in the N-terminal portion of the catalytic domain, and the presence of only six cysteines available for intramolecular disulfide bond formation. However, dog chymase differs in being modified by N-glycosylation. Although the dog chymase catalytic domain exhibits a similar level of sequence identity when compared with both RMCP II and the rat connective tissue mast cell chymase RMCP I (58% and 61%, respectively), the dog enzyme most closely resembles RMCP I in its high predicted net charge (+16) and in the presence of serine at the base of its putative primary substrate binding pocket. The dog chymase differs strikingly from dog mast cell tryptase in the preprosequence and in the structure of the catalytic domain. Therefore, chymase appears not to be closely related to tryptase and may not share a mechanism of activation, even though both enzymes are packaged and released together.

Amino Acid Sequence↗

PubMed1988

Peptide boronic acids, substrate analogs, inhibit chymase, and histamine release from rat mast cells.

Peptide boronic acids, such as methoxysuccinyl-Ala-Ala-Pro-(L)boro-Phe-OH, its pinacol ester, and t-butyloxycarbonyl-Phe-Pro-(L)boro-Phe-pinacol, inhibited the activity of chymase from connective tissue mast cells approximately 40- to 80-fold more than atypical chymase from mucosal mast cells, and did not inhibit trypsin. Only peptide boronic acids containing "L" forms of boronic acids were inhibitory. The Ki values of these peptide boronic acids for chymase were in the 60-170 nM concentration range, like those of the natural inhibitors tested, but all the natural inhibitors tested except Eglin C and chymostatin inhibited both chymase and trypsin. Thus these peptide boronic acids should be useful for selective inhibition of chymase with less inhibitory activity for atypical chymase and without inhibition of trypsin. These peptide boronic acids markedly inhibited histamine release induced by anti-rat immunoglobulin E, suggesting that chymase in connective tissue mast cells plays some role in the process of histamine release. These peptides are assumed to be therapeutically useful for treatment of allergic inflammations catalyzed by chymase.

Animals↗

PubMed1992

Protease composition of exocytosed human skin mast cell protease-proteoglycan complexes. Tryptase resides in a complex distinct from chymase and carboxypeptidase.

We characterized the release and the protease composition of high m.w. complexes released from dispersed human skin mast cells, under conditions that did not disrupt the binding of proteases to proteoglycan. The net percent release ratio of tryptase to histamine, after anti-IgE and calcium ionophore A23187 stimulation was higher than those for chymase or carboxypeptidase. This was explained by the greater cell association of carboxypeptidase and chymase, compared with tryptase, after mast cell degranulation and/or differential cosedimentation of the proteases with mast cells, because treatment of activated mast cells with 1 M NaCl increased the release ratios of chymase and carboxypeptidase more than that of tryptase. Tryptase, after release, was stable in 0.12 M NaCl and had a molecular mass of approximately 200 to 250 kDa, suggesting that it was bound to proteoglycan. We demonstrated that complexes containing chymase and carboxypeptidase were separable from tryptase-containing complexes by gel filtration and by affinity chromatography. First, on fast protein liquid chromatography, released tryptase filtered at a molecular mass of approximately 200 to 250 kDa, compared with chymase and carboxypeptidase at 400 to 560 kDa. Second, by using affinity chromatography with immobilized antitryptase mAb in 0.15 M NaCl, carboxypeptidase and chymase activities were recovered primarily in the effluent and washes of an antitryptase antibody affinity column and cofiltered at 400 to 560 kDa. Tryptase was recovered only in the eluate. Finally, by using potato tuber carboxypeptidase inhibitor-Sepharose affinity chromatography, tryptase activity was found primarily in the effluent and washes, filtered at a molecular mass of 200 kDa on fast protein liquid chromatography, and was stable in 0.12 M NaCl buffer at 37 degrees C. Carboxypeptidase and chymase activities were found primarily in the eluate. These findings suggest that tryptase and carboxypeptidase/chymase reside in distinct macromolecular complexes. Separate complexes containing these proteases may help explain previous ultrastructural observations in which the distributions of chymase and tryptase within a single granule did not always coincide.

Carboxypeptidases↗