Functional constituents of the active site of human neutrophil collagenase

Catalytic site studies on tuna (Thunnus albacares) pyloric caeca aminopeptidase

Tuna pyloric caeca aminopeptidase (tAP) is a glycosylated zinc-metalloenzyme containing apparently two identical subunits. The enzyme is reversibly inhibited in a time-dependent manner by amastatin. Slow development of tAP inhibition by this inhibitor could be demonstrated. Dissociation of the complex of tAP with amastatin is also slow. Two molar equivalents of the inhibitor are bound by the enzyme suggesting the presence of one catalytic site in each subunit. Chemical modification of tAP with 1-cyclohexyl-3-(2-morpholinoethyl) carbonyl-metho-p-toluene sulfonate and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinone revealed the presence of essential acidic amino acid residues probably located at the active site. Compatible with the presence of arginine and tyrosine residues at the catalytic site of most metalloproteinases, tAP is reversibly inhibited by phenylglyoxal and inactivated by tetranitromethane in a time-dependent fashion. The rate of inhibition by these modifiers could be significantly decreased if the enzyme was previously treated with amastatin suggesting that the modified amino acid residues are located at the catalytic site. Diethylpyrocarbonate did not affect the activity of both native and zinc-depleted tAP suggesting that histidine is not involved in the zinc-ligand formation.

Identification of the thyrotropin-releasing-hormone-degrading ectoenzyme as a metallopeptidase

A time-dependent inhibition of the thyrotropin-releasing-hormone (TRH)-degrading ectoenzyme (EC 3.4.19.-) from rat brain by the metal-complexing agents imidazole, NaCN, EDTA and 1,10-phenanthroline could be demonstrated. In contrast, the inhibition by the non-chelating analogues 4,7- and 1,7-phenanthroline was not time-dependent. At a concentration of 100 microM EDTA the enzymic activity decreased by 50% only after pretreatment for 6 h. It could be restored by addition of Zn2+, Ni2+ and Co2+ but not by other transition metal ions and also not by Ca2+ and Mg2+. Without pretreatment, the enzyme was activated by Co2+ and inhibited by Cu2+, Cd2+ and Hg2+ in a time-dependent manner, but remained unaffected by Ni2+ and Mn2+, as well as by Ca2+ and Mg2+. Compatible with the His-Glu-Xaa-Xaa-His consensus sequence of most zinc-containing metallopeptidases, chemical modification studies with carbodiimide revealed the presence of an essential acidic amino acid residue, probably located at the active site of the enzyme. The catalytically active metal ion could be exchanged for 65Zn and the enzyme could be effectively inhibited by L-pyroglutamyl hydroxamic acid, the chelating derivative of the TRH cleavage product pyroglutamic acid. The TRH-degrading ectoenzyme thus classifies as a member of the zinc-dependent metallopeptidase family.

Purification to homogeneity of latent and active 58-kilodalton forms of human neutrophil collagenase

Latent and active 58-kDa forms of human neutrophil collagenase (HNC) have been purified to homogeneity. Buffy coats were extracted in the presence and absence of phenylmethanesulfonyl fluoride to generate crude starting preparations that contained latent and active HNC, respectively. The buffers used in preparing these extracts and for all subsequent chromatographic steps contained NaCl at a concentration of 0.5 M or greater, 0.05% Brij-35, concentrations of CaCl2 of 5 mM or greater, and (when feasible) 50 microM ZnSO4 to stabilize the HNC. The collagenase activity in the buffy coat extracts was adsorbed to a Reactive Red 120-agarose column at pH 7.5 in 0.5 M NaCl and was eluted when the NaCl concentration was increased to 1 M. The active and p-(chloromercuri)benzoate-activated latent enzymes were next adsorbed to a Sepharose-CH-Pro-Leu-Gly-NHOH affinity resin in 1 M NaCl at pH 7.5 and desorbed at pH 9 to give a fraction containing only HNC and a small amount of neutrophil gelatinase. The latter enzyme was removed by passage over a gelatin-Sepharose column in 1 M NaCl at pH 7.5. The purified samples of active and latent HNC were obtained with typical cumulative yields of 32 and 82% and specific activities toward soluble rat type I collagen at 30 degrees C of 7200 and 12,000 micrograms min-1 mg-1, respectively. These specific activities are markedly higher than previously reported for HNC. Both active and latent HNC exhibit a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis both in the presence and in the absence of 2-mercaptoethanol. The mobility of latent HNC is consistent with a molecular weight of approximately 58K, with the active form exhibiting a slightly lower (less than 1-2K) molecular weight.

The effect of pH, temperature, and D2O on the activity of porcine synovial collagenase and gelatinase

The pH dependence of Vmax and Vmax/Km for hydrolysis of Dnp-Pro-Leu-Gly-Leu-Trp-Ala-D-Arg-NH2 at the Gly-Leu bond by porcine synovial collagenase and gelatinase was determined in the pH range 5-10. Both enzymes exhibited bell-shaped dependencies on pH for these two kinetic parameters, indicating that activity is dependent on at least two ionizable groups, one of which must be unprotonated and the other protonated. For collagenase, Vmax/Km data indicate that in the substrate-free enzyme, these groups have apparent pK values of 7.0 and 9.5, while the Vmax profile indicates similar pK values of 6.8 and 10.1 for the enzyme-substrate complex. The corresponding pH profiles of gelatinase were similar to those of collagenase, indicating the importance of groups with apparent pK values of 5.9 and 10.0 for the free enzyme and 5.9 and 11.1 for the enzyme-substrate complex. When these kinetic constants were determined in D2O using the peptide substrate, there was no significant effect on Vmax or Km for collagenase or Km for gelatinase. However, there was a deuterium isotope effect of approximately 1.5 on Vmax for gelatinase. These results indicate that a proton transfer step is not involved in the rate-limiting step for collagenase, but may be limiting with gelatinase. The Arrhenius activation energies for peptide bond hydrolysis of the synthetic peptide as well as the natural substrates were also determined for both enzymes. The activation energy (81 kcal) for hydrolysis of collagen by collagenase was nine times greater than that determined for the synthetic substrate (9.2 kcal). In contrast, the activation energy for hydrolysis of gelatin by gelatinase (26.3 kcal) was only 2.4 times greater than that for the synthetic substrate (11 kcal).

Characterization and activation of procollagenase from human polymorphonuclear leucocytes. N-terminal sequence determination of the proenzyme and various proteolytically activated forms

Procollagenase of human polymorphonuclear leucocytes was purified to homogeneity using a rapid and reproducible method. The purification procedure included affinity chromatography on zinc chelate Sepharose, ion exchange chromatography on Q-Sepharose fast flow, followed by affinity chromatography on orange Sepharose and finally a gel-permeation step on Sephacryl S-300. It was shown by SDS/PAGE, under reducing conditions, that the latent collagenase of human polymorphonuclear leucocytes consists of a single polypeptide chain with an apparent relative molecular mass of 85,000. Upon deglycosylation by endoglycosidase F digestion, the apparent relative molecular mass of the procollagenase was reduced to 53,000 which is similar to that of the fibroblast enzyme, and indicates a close relationship between both enzymes. Sequence data were determined by direct automated Edman degradation of the purified polymorphonuclear leucocyte procollagenase. The complete sequence of the propeptide region (residue 1-120) was thereby established. The proteolytic activation of the polymorphonuclear leucocyte procollagenase by various enzymes was investigated by determining the N-terminal sequences of the intermediate and final activated forms. Activation by chymotrypsin and cathepsin G led to the active form (Mr 64,000) by cleaving 79 N-terminal residues from the proenzyme. Trypsin activates in a two-step process. Cleavage of 48 N-terminal residues led to a still latent Mr 70,000 species. The final active form (Mr 65,000) was obtained by splitting off 20 additional N-terminal residues.

Activation of neutrophil collagenase by cathepsin G

Collagenase is secreted from neutrophils as a latent or proenzyme. In an effort to understand the mechanism of collagenase activation in inflammation, human peripheral neutrophils (PMNs) were isolated and incubated with the tumor promotor, phorbol myristate acetate (PMA), which induces the neutrophils to degranulate and secrete proteinases. Neutrophil media were then treated with various activators or inhibitors of collagenase and other proteinases, and the collagenase activity was measured. A serine proteinase secreted from neutrophils, cathepsin G, was found to activate latent collagenase, but it was also found to require activation itself. Both hypochlorous acid (HOCl) and oxidized glutathione (GSSG) were tested for their collagenase-activating ability and were found to be successful only in the presence of active cathepsin G. A specific cathepsin G inhibitor (0.5 mM Z-Gly-Leu-Phe-CH2Cl) prevented the activation of latent collagenase by HOCl. To confirm these results, purified neutrophil cathepsin G was incubated with a neutrophil proteinase mixture which contained latent collagenase. The collagenase was shown to be activated upon incubation with purified cathepsin G. These results indicate that cathepsin G is a key mediator in neutrophil collagenase activation.