Fragments of human fibroblast collagenase: interaction with metalloproteinase inhibitors and substrates

Polyphenolic profile and ethno pharmacological activities of Callistemonsubulatus (Cheel) Craven leaves cultivated in Egypt

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Callistemon (syn. Melaleuca) of the myrtle family (Myrtaceae) has been documented as an integral part in the ethnobotanical system of the indigenous people of Australian mainland and many of its islands. Several Callistemons including the species subulatus were used by aboriginal Australians for making rafts, roofs for shelters, bandages, and food recipes, in addition to the management of wounds, infections, pain, cough, bronchitis, and gastrointestinal tract (GIT) disorders.

AIM OF THE STUDY

The current study is designed to document the therapeutic effect of the aqueous methanolic extract (AME) of C. sabulatus Chell (syn. M. sabulata) leaves in the management of diarrhea and pain. Also, its influence on additional pharmacological modalities that are related to oxidative stress just as skin aging. Ultimately, the polyphenolic profile of the extract is disclosed and correlated to the aforementioned bioactivities.

MATERIALS AND METHODS

The extract was fractionated using various chromatography techniques and the structures of the isolated compounds were determined based on their chemical and spectral data. The antioxidant activity was assessed using multiple models, including 2,2-diphenyl-picrylhydrazyl (DPPH), oxygen radical absorbance capacity (ORAC) and β-carotene bleaching assays. The anti-skin aging effect was evaluated using different relevant enzymatic assays. The antinociceptive activity was investigated using acetic acid-induced writhing, hot plate test, and formalin-induced paw licking in mice models. The antidiarrheal activity was gauge using the castor oil induced diarrhea, enter pooling and gastrointestinal motility in vivo models.

RESULTS

Diverse polyphenols, including quercetin-3-O-β-D-glucuronopyranoside (1), kaempferol-3-O-β-D-glucuronopyranoside (2), strictinin (3), quercetin-3-O-(2``-O-galloyl)-β-D-glucuronopyranoside (4), afzelin (5), di-galloyl glucose (6), mono-galloyl glucose (7), acacetin (8), apigenin-6,7-dimethyl ether (9), kaempferol trimethyl ether (10), dimethoxy chrysin (11), quercetin (12), kaempferol (13), methyl gallate (14), and gallic acid (15) were identified. The extract exhibited as significant antioxidant activity even better than that of Trolox or BHT. Moreover, it exerts elastase, tyrosinase, and collagenase inhibition activities, in addition to the significant peripheral and central analgesic activity in a dose-dependent manner (P < 0.0001). In castor oil induced diarrhea model, AME significantly prolonged the diarrhea onset, decreased the frequency of defecation, and weight of feces. Likewise, it exhibited a significant reduction in the gastrointestinal motility in charcoal meal model (P < 0.0001) and a considerable inhibitory effect on gastrointestinal transit and peristaltic index with all investigated doses (P < 0.0001).

CONCLUSION

Ethnobotanicals are versatile resources for the management of various ailments by indigenous people and the experimental research is utmost to validate and uncover their pharmacological relevance. C. sabulatus leaves have strong antioxidant, analgesic, anti-skin aging, and antidiarrheal activities which are validated for the first time by various in vitro and in vivo models. The metabolic profile of the unprecedented AME of C. sabulatus leaves compromises a wide array of bioactive polyphenolic metabolites including, flavonoids, tannins, and phenolic acids that are correlated to the observed bioactivities. Altogether, ethnobotanicals with high and diverse contents of polyphenols are potential candidates for the management of various human aliments including neuropathies, GIT disorders, and skin aging conditions.

A Novel Biochemical Study of Anti-Ageing Potential of Eucalyptus Camaldulensis Bark Waste Standardized Extract and Silver Nanoparticles

Eucalyptus camaldulensis Dehnh belongs to family Myrtaceae. They are massive in Egypt. Although reputed for high phenolic content, barks are considered waste. Ageing is a natural phenomenon caused by apoptosis and senescence resulting in wrinkles. The phytochemical analysis of the 70% ethanolic Eucalyptus camaldulensis bark extract (EBE) and evaluation of its anti-ageing potential and as silver nanoparticles (AgNPs) were conducted in this study. Ultra performance liquid chromatography / electrospray ionization mass spectrometry of EBE fingerprint revealed twenty compounds, where Rutin was major. EBE was standardized to contain 1.26 % Rutin. AgNPs synthesized by green synthesis, were characterized by transmission electron microscope and zeta potential measurement. Both EBE and AgNPs were subjected to MTT assay in HFB4 cells and cell cycle arrest. Flow cytometry was used to assess apoptosis and p16 ^INK4a. Genetic expression of p53 and p21 and telomerase level were determined. Anti-wrinkle enzyme assays were done. AgNps were spherical, 468.7 nm in size and with Poly dispersity index of 0.817 ± 0.129. EBE and AgNPs with IC₅₀ 0.156 mg/mL ± 0.05 and 2.315 ± 0.07 μg/mL expressed significant difference in % of cells (DNA content) at G2/M, apoptotic cells numbers, p53 and p21expression and p16^INK4a vs aged cells (P < 0.0001). Both expressed significant increase in telomerase (P < 0.0001). They exhibited elastase, collagenase and tyrosinase inhibition (75 ± 4.3 and 75.9 ± 6.8 % at 300 μg/mL, 58 ± 4.8 and 63 ± 2.3, at 500 μg/mL, 51 ± 4.8 and 65 ± 5.87, at 500 μg/mL, respectively. Although it is considered waste, EBE and Ag NPs are anti-ageing candidates as they inhibit apoptosis, senescence and prevent wrinkles formation.

NMR-Based Metabolomics Profiling for Radical Scavenging and Anti-Aging Properties of Selected Herbs

Herbs that are usually recognized as medicinal plants are well known for their therapeutic effects and are traditionally used to treat numerous diseases, including aging. This study aimed to evaluate the metabolite variations among six selected herbs namely Curcurma longa, Oenanthe javanica, Vitex negundo, Pluchea indica, Cosmos caudatus and Persicaria minus using proton nuclear magnetic resonance (¹H-NMR) coupled with multivariate data analysis (MVDA). The free radical scavenging activity of the extract was measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azinobis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) and oxygen radical absorbance capacity (ORAC) assay. The anti-aging property was characterized by anti-elastase and anti-collagenase inhibitory activities. The results revealed that P. minus showed the highest radical scavenging activities and anti-aging properties. The partial least squares (PLS) biplot indicated the presence of potent metabolites in P. minus such as quercetin, quercetin-3-O-rhamnoside (quercitrin), myricetin derivatives, catechin, isorhamnetin, astragalin and apigenin. It can be concluded that P. minus can be considered as a potential source for an anti-aging ingredient and also a good free radical eradicator. Therefore, P. minus could be used in future development in anti-aging researches and medicinal ingredient preparations.

Antioxidant, anti-collagenase and anti-elastase activities of Phyllanthus emblica, Manilkara zapota and silymarin: an in vitro comparative study for anti-aging applications

Context Phyllanthus emblica L. (Euphorbiaceae) (amla), Manilkara zapota L.P. Royen (Sapotaceae) (sapota) and silymarin are reported to contain antioxidant effects. However, information on other biological activities relating to the anti-aging properties is limited. Objective To compare in vitro antioxidants, anti-collagenase (MMP-1 and MMP-2) and anti-elastase properties as well as the phenolic and flavonoid contents of amla, sapota and silymarin as potential anti-aging ingredients. Materials and methods The ethanol amla and sapota fruit extracts were prepared by three cycles of maceration with 24 h duration each. The total phenolic (TPC) and flavonoid (TFC) contents were determined. The antioxidant capacity was evaluated by DPPH and ABTS assays. The effects of MMP-1, MMP-2 and elastase inhibitions were determined by using the EnzChek® assay kits (Molecular-Probes, Eugene, OR). Results Amla exhibited the highest in TPC (362.43 ± 11.2 mg GAE/g) while silymarin showed the highest in TFC (21.04 ± 0.67 mg QE/g). Results of antioxidant activity by DPPH and ABTS methods showed that amla possessed the most potent capacity with IC50 values of 1.70 ± 0.07 and 4.45 ± 0.10 μg/mL, respectively. Highest inhibitions against MMP-1, MMP-2 and elastase were detected for sapota with IC50 values of 89.61 ± 0.96, 86.47 ± 3.04 and 35.73 ± 0.61 μg/mL, respectively. Discussion and conclusion Test extracts offered anti-aging properties in different mechanisms. Amla showed the highest phenolic content and antioxidant property with moderate anti-collagenase. Silymarin exhibited measurable flavonoid content with anti-elastase effect. Sapota showed the highest collagenase and elastase inhibitions with moderate antioxidant effect. Thus, extracts might be added as a mixture to gain the overall anti-aging effects.

Matrix metalloproteinase-1 and thrombin differentially activate gene expression in endothelial cells via PAR-1 and promote angiogenesis

Many tumor types express matrix metalloproteinase-1 (MMP-1); its collagenase activity facilitates both tumor cell invasion and metastasis. MMP-1 expression is also associated with increased angiogenesis; however, the exact mechanism by which this occurs is not clear. MMP-1 proteolytically activates protease activated receptor-1 (PAR-1), a thrombin receptor that is highly expressed in endothelial cells. Thrombin is also present in the tumor microenvironment, and its activation of PAR-1 is pro-angiogenic. It is currently unknown whether MMP-1 activation of PAR-1 induces angiogenesis in a similar or different manner compared with thrombin. We sought to determine the mechanism by which MMP-1 promotes angiogenesis and to compare the effects of MMP-1 with those of thrombin. Our results demonstrate that via PAR-1, MMP-1 activates mitogen-activated protein kinase signaling cascades in microvessel endothelial cells. Although thrombin activation of PAR-1 also induces signaling through these pathways, the time-course of activation appears to vary. Gene expression analysis revealed a possible consequence of these signaling differences as MMP-1 and thrombin induce expression of different subsets of pro-angiogenic genes. Furthermore, the combination of thrombin and MMP-1 is more angiogenic than either protease alone. These data demonstrate that MMP-1 acts directly on endothelial cells as a pro-angiogenic signaling molecule and also suggest that the effects of MMP-1 may complement the activity of thrombin to better facilitate angiogenesis and promote tumor progression.

The mammalian chitinase-like lectin, YKL-40, binds specifically to type I collagen and modulates the rate of type I collagen fibril formation

YKL-40 is expressed in arthritic cartilage and produced in large amounts by cultured chondrocytes, but its exact role is unclear, and the identities of its physiological ligands remain unknown. Purification of YKL-40 from resorbing bovine nasal cartilage and chondrocyte monolayers demonstrated the existence of three isoforms, a major and minor form from resorbing cartilage and a third species from chondrocytes. Affinity chromatography experiments with purified YKL-40 demonstrated specific binding of all three forms to collagen types I, II, and III, thus identifying collagens as potential YKL-40 ligands. Binding to immobilized type I collagen was inhibited by soluble native ligand, but not heat-denatured ligand, confirming a specific interaction. Binding of the chondrocyte-derived species to type I collagen was also demonstrated by surface plasmon resonance analysis, and the dissociation rate constant was calculated (3.42 x 10(-3) to 4.50 x 10(-3) s(-1)). The chondrocyte-derived species was found to prevent collagenolytic cleavage of type I collagen and to stimulate the rate of type I collagen fibril formation in a concentration-dependent manner. By contrast, the cartilage major form had an inhibitory effect on type I collagen fibrillogenesis. Digestion with N-glycosidase F, endoglycosidase H and lectin blotting did not reveal any difference in the carbohydrate component of these two YKL-40 species, indicating that this does not account for the opposing effects on fibril formation rate.

The interaction of metal ions and Marimastat with matrix metalloproteinase 9

The effect of a range of metal ions on the ability of Marimastat to inhibit matrix metalloproteinase 9 (MMP-9) was examined in a fluorescence based proteolytic assay. Whilst none of the metals examined significantly affected the inhibitory ability of Marimastat, several metal ions did have a significant effect on MMP-9 activity itself. In the absence of Marimastat, Zn(II) and Fe(II) significantly inhibited MMP-9 activity at metal ion concentrations of 10 and 100 microM, respectively. In both the absence and presence of Marimastat, Cd(II) significantly inhibited MMP-9 at 100 microM. In contrast, 1 mM Co(II) significantly upregulated MMP-9 proteolytic activity.

Unexpected crucial role of residue 272 in substrate specificity of fibroblast collagenase

Degradation of type I collagen by collagenases is an important part of extracellular remodeling. To understand the role of the hinge region of fibroblast collagenase in its collagenolytic activity, we individually substituted the 10 conserved amino acid residues at positions 264, 266, 268, 296, 272, 277, 284, 289, 307, and 313 in this region of the enzyme by their corresponding residues in MMP-3, a noncollagenolytic matrix metalloproteinase. The general proteolytic and triple helicase activities of all of the enzymes were determined, and their abilities to bind to type I collagen were assessed. Among the mutants, only G272D mutant enzyme exhibited a significant change in type I collagenolysis. The alteration of the Gly(272) to Asp reduced the collagenolytic activity of the enzyme to 13% without affecting its general proteolytic activity, substrate specificity, or the collagen binding ability. The catalytic efficiency of the G272D mutant for the triple helical peptide substrate [C(6)-(GP- Hyp)(4)GPL(Mca)GPQGLRGQL(DPN)GVR(GP-HYP)(4)-NH(2)](3) and the peptide substrate Mca-PLGL(Dpa)AR-NH(2) and its dissociation constant for the triple helical collagen were similar to that of the wild type enzyme, indicating that the presence of this residue in fibroblast collagenase is particularly important for the efficient cleavage of type I collagen. Gly(272) is evidently responsible for the hinge-bending motion that is essential for allowing the COOH-terminal domain to present the collagen to the active site.

Discovery of chemokine substrates for matrix metalloproteinases by exosite scanning: a new tool for degradomics

Increasingly it is being recognized that matrix metalloproteinases (MMPs) are important processing enzymes that regulate cellular behaviour and immune cell function by selective proteolysis of cell surface receptors and adhesion molecules, cytokines and growth factors. These functions will likely prove to be as important in vivo as the proposed roles of MMPs in pathological matrix degradation. To screen for new protease substrates we have reported a novel 'exosite scanning' strategy that utilizes protease substrate-binding exosite domains as yeast two-hybrid baits. We discovered that the chemokine monocyte chemoattractant protein-3 (MCP-3) binds the hemopexin C domain of gelatinase A (MMP-2) leading to its efficient cleavage, converting an agonist to a potent receptor antagonist. We have now found that other MMPs cleave MCP-1, MCP-2, MCP-3, MCP-4, SDF-lalpha and SDF-1beta indicating that the intersection between the chemokine and MMP families is broad with important implications for the control of inflammatory and immune processes. Use of engineered substrates with altered exosite binding affinities further revealed the power of exosites in dictating proteolytic specificity - either directing cleavage of non-preferred sites or in other cases virtually eliminating proteolysis of readily accessible scissile bonds. Hence, bioinformatic searches for protease substrates based on scissile bond preference will only reveal a subset of substrates unless the influence of exosites is considered.

The oxidative inactivation of tissue inhibitor of metalloproteinase-1 (TIMP-1) by hypochlorous acid (HOCI) is suppressed by anti-rheumatic drugs

Tissue inhibitors of metalloproteinases (TIMPs) prevent uncontrolled connective tissue destruction by limiting the activity of matrix metalloproteinases (MMPs). That TIMPs should be susceptible to oxidative inactivation is suggested by their complex tertiary structure which is dependent upon 6 disulphide bonds. We examined the oxidative inactivation of human recombinant TIMP-1 (hr TIMP-1) by HOCl and the inhibition of this process by anti-rheumatic agents. TIMP-1 was exposed to HOCl in the presence of a variety of disease modifying anti-rheumatic drugs. TIMP-1 activity was measured by its ability to inhibit BC1 collagenase activity as measured by a fluorimetric assay using the synthetic peptide substrate (DNP-Pro-Leu-Ala-Leu-Trp-Ala-Arg), best cleaved by MMP-1. The neutrophil derived oxidant HOCl, but not the derived oxidant N-chlorotaurine, can inactivate TIMP-1 at concentrations achieved at sites of inflammation. Anti-rheumatic drugs have the ability to protect hrTIMP-1 from inactivation by HOCl. For D-penicillamine, this effect occurs at plasma levels achieved with patients taking the drug but for other anti-rheumatic drugs tested this occurs at relatively high concentrations that are unlikely to be achieved in vivo, except possibly in a microenvironment. These results are in keeping with the concept that biologically derived oxidants can potentiate tissue damage by inactivating key but susceptible protein inhibitors such as TIMP-1 which form the major local defence against MMP induced tissue breakdown.

Collagen zymography as a sensitive and specific technique for the determination of subpicogram levels of interstitial collagenase

We describe the use of casting native collagen type I in SDS-polyacrylamide gel (collagen zymography) for the determination of interstitial collagenase. As with gelatin, the incorporation of collagen in the gels reduced protein migration and the need for making corrections for an accurate Mr evaluation. This method proved to be very sensitive: 0.1 pg of APMA-activated procollagenase could be detected, and specific levels of active gelatinase or stromelysin lower than 5 ng were inactive under our experimental conditions. It was used to demonstrate the increased expression of collagenase following treatment of human gingival fibroblasts with interleukin-1 beta; the amounts of enzyme quantified by either collagen zymography or immunodot blot assay are comparable.

Computational sequence analysis of the tissue inhibitor of metalloproteinase family

The tissue inhibitor of metalloproteinase (TIMP) family regulates extracellular matrix turnover and tissue remodeling by forming tight-binding inhibitory complexes with matrix metalloproteinases (MMPs). MMPs and TIMPs have been implicated in many normal and pathological processes, such as morphogenesis, development, angiogenesis, and cancer metastasis. This minireview provides information that would aid in classification of the TIMP family and in understanding the similarities and differences among TIMP members according to the physical data, primary structure, and homology values. Calculations of molecular weight, isoelectric point values, and molar extinction coefficients are reported. This study also compares sequence similarities and differences among the TIMP members through calculations of homology within their individual loop regions and the mature region of the molecule. Lastly, this report examines structure-function relationships of TIMPs. Thorough knowledge of TIMP primary and tertiary structure would facilitate the uncovering of the molecular mechanisms underlying metalloproteinase, inhibitory activities and biological functions of TIMPs.

Catalytic domain comparisons of human fibroblast-type collagenase, stromelysin-1, and matrilysin

The propeptide plus the catalytic domain of human fibroblast-type collagenase, stromelysin-1, and matrilysin were expressed in Escherichia coli to directly compare the properties of all three catalytic domains utilizing the same assays. Truncated fibroblast-type collagenase (mini-CL), truncated stromelysin-1 (mini-SL-1), and matrilysin, like their native counterparts, could be activated by organomercurials, trypsin, or SDS. The mini-CL and mini-SL-1 displayed catalytic properties similar to their native counterparts, except that the mini-CL could not cleave native type I collagen. The k(cat)/Km for matrilysin (355 microM(-1) h(-1)) on the synthetic Mca-peptide was much higher than that for mini-CL (69 microM(-1) h(-1)) or mini-SL-1 (23.6 microM(-1) h(-1)). Mini-SL-1 and matrilysin, but not mini-CL, were capable of superactivating collagenase thus increasing the rate of collagen cleavage. Mini-CL and mini-SL-1, but not matrilysin, were able to form SDS-stable complexes with TIMP-1 when co-incubated with an organomercurial and TIMP-1. The second-order rate constant (k(on)) for TIMP-1 inhibition of mini-CL and mini-SL-1 were similar, 0.635 x 10(5) M(-1) s(-1) and 1.52 x 10(5) M(-1) s(-1), respectively. The k(on) for TIMP-1 inhibition of matrilysin was lower (0.130 x 10(5) M(-1) s(-1)) supporting the observation that no SDS stable complexes were detected. This study demonstrates that these catalytic domains are distinct and play a major role in the specificity of these enzymes in regard to rate of catalysis, TIMP-1 binding, and superactivation of collagenase.

The hemopexin-like domain (C domain) of human gelatinase A (matrix metalloproteinase-2) requires Ca2+ for fibronectin and heparin binding. Binding properties of recombinant gelatinase A C domain to extracellular matrix and basement membrane components

The binding properties of the COOH-terminal hemopexin-like domain (C domain) of human gelatinase A (matrix metalloproteinase-2, 72-kDa gelatinase) were investigated to determine whether the C domain has binding affinity for extracellular matrix and basement membrane components. Recombinant C domain (rC domain) (Gly417-Cys631) was expressed in Escherichia coli, and the purified protein, identified using two antipeptide antibodies, was determined by electrospray mass spectrometry to have a mass of 25,925 Da, within 0.1 Da of that predicted. As assessed by microwell substrate binding assays and by column affinity chromatography, the matrix proteins laminin, denatured type I collagen, elastin, SPARC (secreted protein that is acidic and rich in cysteine), tenascin, and MatrigelTM were not bound by the rC domain. Unlike the hemopexin-like domains of collagenase and stromelysin, the rC domain also did not bind native type I collagen. Nor were native or denatured types II, IV, V, and X collagen, or the NC1 domain of type VII collagen bound. However, binding to heparin and fibronectin (Kd, 1.1 x 10(-6) M) could be disrupted by 0.58-0.76 and 0.3 M NaCl, respectively. Using nonoverlapping chymotrypsin-generated fragments of fibronectin, binding sites for the rC domain were found on both the 40-kDa heparin binding and the 120-kDa cell binding fibronectin domains (Kd values, approximately 4-6 x 10(-7) M). The Ca2+ ion, but not the potential structural Zn2+ ion, were found to be essential for maintaining the binding properties of the protein. The apo-form of the rC domain did not bind heparin, and both ethylenediaminetetraacetic acid and the specific Ca2+ ion chelator 1, 2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid, but not the Zn2+ ion chelator 1,10-phenanthroline, eluted the holo form of the rC domain from both heparin-Sepharose and fibronectin. Inductive coupled plasma mass spectrometry also did not detect a Zn2+ ion in the rC domain. In contrast, reduction with 65 mM dithiothreitol did not interfere with heparin binding, further emphasizing the crucial structural role played by the Ca2+ ion. Together, these data demonstrate for the first time that the hemopexin-like domain of gelatinase A has a binding site for fibronectin and heparin, and that Ca2+ ions are important in maintaining the structure and function of the domain.

The catalytic domain of activated collagenase I (MMP-1) is absolutely required for interaction with its specific inhibitor, tissue inhibitor of metalloproteinases-1 (TIMP-1)

Here, we describe the production of recombinant human tissue inhibitor of metalloproteinases-1 (rTIMP-1) and wild-type and mutant human collagenase type I (rMMP-1) proteins in SF9 cells by the baculovirus expression system. Wild-type MMP-1, as well as the MMP-1 mutant lacking the C-terminal hemopexin-like domain [des-(248-450)-MMP-1], exhibit enzymatic activity upon cleavage of the prodomain by treatment with trypsin or 4-aminophenylmercuric acetate. Enzyme activity of both proteins can be inhibited by addition of rTIMP. Deletion of the complete active-site [des-(161-228)-MMP-1] within the catalytic domain, or mutation of a single His residue of the Zn2+ binding domain (His199), generates stable forms of MMP-1 proteins which are unable to digest collagen type I or beta-casein. In addition to co-immunoprecipitation analysis, we have established a rapid and sensitive ELISA assay using immobilized rTIMP to determine the structural requirements of MMP-1 to form complexes with its inhibitor. Only the activated and not the latent forms of wild-type and C-terminal mutant des-(248-450)-MMP-1 proteins are able to form complexes with TIMP. Neither mutation of His199, nor deletion mutants des-(161-228)-MMP-1 and des-(161-228/248-450)-MMP-1, interact with TIMP. This demonstrates that the C-terminal hemopexin domain of MMP-1, in contrast to the corresponding regions of gelatinase A and gelatinase B, does not interact with TIMP-1. In summary, we have shown that the integrity of the catalytic domain of MMP-1 and its ability to bind Zn2+ is absolutely required for complex formation with TIMP-1, which further underlines the importance of this region for proper regulation of enzymatic activity of MMP-1.

The mechanism of inhibition of collagenase by TIMP-1

Tissue inhibitor of metalloproteinase-I (TIMP-1) is a slow, tight-binding inhibitor of fibroblast-type collagenase. Time-course data from inhibition experiments were analyzed by graphic analysis, by nonlinear regression of the analytic integrals of the rate equations and by nonlinear regression with numeric integration of the rate equations. With the same assumptions, approximations and data, all three methods of analysis produced the same model preferences and values for the kinetic parameters. The time-course data for the inhibition of fibroblast-type collagenase by TIMP-1 are best described by the equations for a noncompetitive two-step mechanism, in which an inactive, rapidly formed, reversible complex slowly forms an inactive, tight complex. However, from the analysis of data from experiments at concentrations of TIMP-1 comparable to that of collagenase, it is apparent that free TIMP-1 also functions in the breakdown of the tight complex. The rapidly formed complex has a dissociation constant of 8 nM and reacts to the tight complex with a first-order rate constant of 0.003 s-1. The back reaction of the tight complex to the rapid complex has a second-order rate constant of 5 x 10(4) M-1 s-1. The resulting global dissociation constant of the tight complex is 0.1 nM at 3 nM TIMP-1 and collagenase concentration. Collagenase without the carboxyl-terminal domain (mini-collagenase) is inhibited by TIMP-1 according to a mechanism, in which the rapidly formed complex has such a high dissociation constant (247 nM) that it effectively constitutes a one-step mechanism, in which TIMP-1 binds with an apparent second-order rate constant of 9.6 x 10(4) mol-1 s-1 and the enzyme-TIMP-1 complex dissociates with a first order rate constant of 0.00026 s-1. The apparent global dissociation constant for the tight complex (2.7 nM) is higher than that for the fibroblast-type collagenase. Participation of TIMP-1 in the dissociation is not demonstrable. Therefore, the carboxyl-terminal domain of fibroblast-type collagenase is important for the initial, rapid binding of TIMP-1 and the initial complex contributes to the overall binding.

Collagenase: a key enzyme in collagen turnover

The primary agents responsible for cartilage and bone destruction in joint diseases are active proteinases that degrade collagen and proteoglycan. All four main classes of proteolytic enzymes are involved in either the normal turnover of connective tissue or its pathological destruction. These proteinases are made by different cells found within the joints. Both extracellular and intracellular pathways exist and individual enzymes can be inhibited by specific proteinaceous inhibitors that block their activity. Recent research has implicated the matrix metalloproteinases (MMPs) in many of the processes involved in joint diseases. The metalloproteinases are capable of degrading all components of the extracellular matrix. This family of proteinases contains a group of at least three collagenases that are capable of degrading native fibrillar collagen. Collagen degradation within joint disease is recognized as the irreversible step in the destruction of cartilage that leads to a failure in joint function. The collagenases are the enzymes necessary to initiate collagen turnover in normal connective tissue turnover and in disease.

Metalloproteinase inhibitors and the prevention of connective tissue breakdown

The primary agents responsible for cartilage and bone destruction in joint diseases are active proteinases degrading collagen and proteoglycan. All four main classes of proteolytic enzymes are involved in either the normal turnover of connective tissue or its pathological destruction. These proteinases are made by different cells found within the joints. Both extracellular and intracellular pathways exist, and individual enzymes can be inhibited by specific proteinaceous inhibitors that block their activity. Recent research has implicated the matrix metalloproteinases in many of the processes involved in joint diseases. Conventional treatments do little to affect the underlying disease processes, and recently, the use of proteinase inhibitors has been suggested as a new therapeutic approach. A large variety of different synthetic approaches have been used and highly effective metalloproteinase inhibitors have been designed, synthesised and tested. These metalloproteinase inhibitors can prevent the destruction of animal cartilage in model systems and slow the progression of human tumours. Future patient trials will test the effectiveness of these compounds in vivo for the treatment of joint diseases.

Structure of full-length porcine synovial collagenase reveals a C-terminal domain containing a calcium-linked, four-bladed beta-propeller

BACKGROUND

The collagenases are members of the family of zinc-dependent enzymes known as the matrix metalloproteinases (MMPs). They are the only proteinases that specifically cleave the collagen triple helix, and are important in a large number of physiological and pathological processes. Structures are known for the N-terminal catalytic' domain of collagenases MMP-1 and MMP-8 and of stromelysin (MMP-3). This catalytic domain alone, which comprises about 150 amino acids, has no activity against collagen. A second domain, of 200 amino acids, is homologous to haemopexin, a haem-binding glycoprotein.

RESULTS

The crystal structure of full-length MMP-1 at 2.5 A resolution gives an R-factor of 21.7%. Two domains are connected by an exposed proline-rich linker of 17 amino acids, which is probably flexible and has no secondary structure. The catalytic domain resembles those previously observed, and contains three calcium-binding sites. The haemopexin-like domain contains four units of four-stranded antiparallel beta sheet stabilized on its fourfold axis by a cation, which is probably calcium. The domain constitutes a four-bladed beta-propeller structure in which the blades are scarcely twisted.

CONCLUSIONS

The exposed linker accounts for the difficulty in purifying full-length collagenase. The C-terminal domain provides a structural model for haemopexin and its homologues. It controls the specificity of MMPs, affecting both substrate and inhibitor binding, although its role remains obscure. These structural results should aid the design of site-specific mutants which will reveal further details of the specificity mechanism.

A helping hand for collagenases: the haemopexin-like domain

The structures of the C-terminal domains of rabbit haemopexin and full-length porcine fibroblast collagenase reveal a common beta-propeller fold with pseudo-fourfold symmetry. The interactions of these haemopexin-like domains with target proteins and ligands is, however, still a matter of debate.