Expression and Purification of a Matrix Metalloprotease Transmembrane Domain in Escherichia coli

Membrane tethered matrix metalloproteases are bound to the plasma membrane by a glycosylphosphatidylinositol-anchor or a transmembrane domain. To date, most studies of membrane-bound matrix metalloprotease have focused on the globular catalytic and protein-protein interaction domains of these enzymes. However, the transmembrane domains have been poorly studied even though they are known to mediate intracellular signaling via interaction with various cellular proteins. The expression and purification of the transmembrane domain of these proteins can be challenging due to their hydrophobic nature. In this chapter we describe the purification of a transmembrane domain for a membrane-bound matrix metalloprotease expressed in E. coli and its initial characterization by NMR spectroscopy.

Identification and characterization of an amphioxus matrix metalloproteinase homolog BbMMPL2 responding to bacteria challenge

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases mainly involved in extracellular matrix (ECM) degradation. We have cloned and identified BbMMPL2 as homolog of MMPs from adult amphioxus. Recombinant BbMMPL2 proteins underwent self-processing during refolding in vitro. The final ~23 kDa polypeptide displayed proteolytic activity against ECM components like casein, gelatin, collagen IV and fibrinogen, but not laminin, fibronectin or α1-PI. This activity could be inhibited by GM6001 and TIMP-1/2. In addition, real-time RT-PCR analysis revealed that BbMMPL2 expressed in all issues/organs in adult amphioxus we tested. Its transcription was significantly up-regulated 12 h post immune challenge by Escherichia coli in epidermis and hepatic diverticulum but only slightly increased by Staphyloccocus aureus in epidermis. Furthermore, recombinant BbMMPL2-EGFP expressed in 293T and NIH/3T3 cells showed aggregation in cytoplasm and induced cell death. Our results provided new evidence that MMP was involved in immune response which could be conserved through evolution.

Prevention of ischemia/reperfusion-induced accumulation of matrix metalloproteinases in rat lung by preconditioning with nitric oxide

BACKGROUND

Pulmonary ischemia/reperfusion (I/R) injury is associated with degradation of structural proteins. Preconditioning by short-term inhalation of nitric oxide (NO) ameliorates some of the severe consequences of an I/R cycle. The aim of this study was to evaluate the effects of NO preconditioning on I/R-induced changes of matrix metalloproteinase (MMP) activity.

MATERIALS AND METHODS

Left lung in situ ischemia in rats was maintained for 1 h, followed by reperfusion for 30 min or 4 h. In the NO group, animals inhaled NO (15 ppm) for 10 min directly before ischemia. Changes of expression or activity of MMPs (MMP-2, MMP-7, MMP-9, MMP-14) and of neutrophil elastase (NE) in bronchoalveolar lavage fluid (BALF), lung tissue, and arterial plasma were analyzed by zymography and Western blotting. Western blotting was also used to detect tissue inhibitors of matrix proteases, the extracellular metalloproteinase inducer (EMMPRIN or CD147), and endostatin, a proteolytic collagen fragment.

RESULTS

Ischemia resulted in an increase of lavagable MMP activity (12.3-fold MMP-2, 8.1-fold MMP-7) at 30 min reperfusion. The activity of MMP-9 and NE in lung tissue progressively increased with time, whereas MMP-14 and MMP-2 were constant. Inhalation of NO prevented the early increase of MMP-2 and MMP-7 in BALF, but the level of MMP-9 and NE in tissue was not affected. The expression of tissue inhibitors of matrix proteases and EMMPRIN did not respond to any treatment. The release of endostatin proceeded in parallel to the level of MMPs in BALF. Significant correlations between MMP-9 and myeloperoxidase in lung tissue and between MMP-2/MMP-7 and plasma protein extravasation were found.

CONCLUSIONS

The early rise of MMP-2 and MMP-7 in BALF resulted from plasma protein extravasation, whereas MMP-9 and NE were imported into lung tissue via leukocyte invasion. The effect of NO inhalation on lavagable MMPs was secondary to the sealing of the permeability barrier.

Neural MMP-28 expression precedes myelination during development and peripheral nerve repair

Mammalian matrix metalloproteinase 28 (MMP-28) is expressed in several normal adult tissues, and during cutaneous wound healing. We show that, in frog and mouse embryos, MMP-28 is expressed predominantly throughout the nervous system. Xenopus expression increases during neurulation and remains elevated through early limb development where it is expressed in nerves. In the mouse, neural expression peaks at embryonic day (E) 14 but remains detectable through E17. During frog hindlimb regeneration XMMP-28 is not initially expressed in the regenerating nerves but is detectable before myelination. Following hindlimb denervation, XMMP-28 expression is detectable along regenerating nerves before myelination. In embryonic rat neuron-glial co-cultures, MMP-28 decreases after the initiation of myelination. Incubation of embryonic brain tissue with purified MMP-28 leads to the degradation of multiple myelin proteins. These results suggest that MMP-28 plays an evolutionarily conserved role in neural development and is likely to modulate the axonal-glial extracellular microenvironment.

Characterization of matrix metalloproteinase expressed by human embryonic kidney cells

There is little information available on the proteases expressed by human embryonic kidney (HEK) cells, which are often used for expression of recombinant proteins and production of adenovirus vector. The expression profile of proteases in HEK cell line was investigated using zymography, mRNA analysis, western blotting and protein array. The major protease was gelatinase A [or matrix metalloproteinase (MMP)-2]. Beside, other MMPs, such as MMP-1, -2, -3, -8, -9, -10, -13 and membrane type (MT) 1- and 3-MMP, as well as tissue inhibitors of metalloproteinase (TIMP)-1, -2 and -3, were also expressed by HEK cells. Characterization of MMP and TIMP profiles expressed by HEK cells provides the basis for degradation control of recombinant protein and adenovirus vector during culture and purification processes.

MMP-20 is predominately a tooth-specific enzyme with a deep catalytic pocket that hydrolyzes type V collagen

Matrix metalloproteinase-20 (MMP-20, enamelysin) has a highly restricted pattern of expression. In healthy tissues, MMP-20 is observed in the enamel organ and pulp organ of developing teeth and is present only as an activated enzyme. To identify other tissues that may express MMP-20, we performed a systematic mouse tissue expression screen. Among the non-tooth tissues assayed, MMP-20 transcripts were identified only in minute quantities within the large intestine. The murine Mmp20 promoter was cloned, sequenced, and assessed for potential tooth-specific regulatory elements. In silico analysis identified four promoter modules that were common to Mmp20 and at least two of three coregulated predominantly tooth-specific genes that encode ameloblastin, amelogenin, and enamelin. We asked if the highly restricted MMP-20 expression pattern was associated with a broad substrate specificity that might preclude its expression in other tissues. An iterative mixture-based random doedecamer peptide library screen with Edman sequencing of MMP-20 cleavage products revealed that, among MMPs previously screened, MMP-20 had unique substrate preferences. These preferences indicate that MMP-20 has a deep and wide catalytic pocket that can accommodate substrates with large aromatic residues in the P1' position. On the basis of matrices derived from the peptide library data, we identified and then confirmed that type V collagen is an MMP-20 substrate. Since type V collagen is not present in dental enamel but is an otherwise widely distributed collagen, and since only active MMP-20 has been observed in teeth, our data suggest that control of MMP-20 activity is primarily regulated by transcriptional means.

Activity-Based Matrix Metallo-Protease Enrichment Using Automated, Inhibitor Affinity Extractions

An automated inhibitor affinity extraction method for the activity-based enrichment of matrix metallo-proteases (MMPs) is presented. Samples containing purified MMP-12 were first extracted at different flow rates in a syringe pump setup, using cartridges packed with an MMP inhibitor affinity sorbent based on an immobilized hydroxamic acid containing peptide (PLG-NHOH) with mumol/L MMP affinity. Faster extractions, a reduced number of manual manipulations, and higher extraction yields (98.9%-99.3%) were obtained over the whole flow rate range compared to batch extractions. Application of the method to synovial fluid from a rheumatoid arthritis patient followed by gelatin-zymography revealed a strong enrichment of distinct MMPs from this biological sample that were not clearly visible in the original sample. The use of an auto-sampler and a solid-phase extraction (SPE) workstation allowed full automation of the extraction procedure with the potential for on-line coupling to further sample preparation and analytical steps. MMP-12 extractions were optimized showing that ligand density is an important factor with a clear extraction yield optimum around 5 to 7.5 mmol/L. Conditioning of the stationary phase for 1 week prior to use resulted in a further slight increase in extraction yield. Under optimal conditions, an extraction yield of 99.5% was reached with a cartridge contact time of only 13 s for MMP-12. The efficacy of the extraction method for activity-based MMP profiling was further improved by the use of a broad-spectrum MMP inhibitor with nmol/L affinity (TAPI-2). This resulted in an increased extraction yield for all tested MMPs. For MMP-1, -7, -8, -10, -12, and -13 extraction yields of at least 98.8% were obtained, while for MMP-9 (full length and catalytic domain) an extraction yield of at least 96.1% was reached.

Mapping and partial characterization of proteases expressed by a CHO production cell line

The proteolytic activities expressed by a Chinese hamster ovary (CHO) cell line in the cultivation supernatant during the production of recombinant factor VIII were mapped with a broad spectrum protease assay and a series of different types of protease inhibitors. The destabilizing effect on the product emanated from a metalloproteinase, which could be effectively blocked by chelating agents to lead to product stabilization. Amino acid sequences of the isolated metalloproteinase were found to have sequence homology with matrix metalloproteinases (MMPs) MMP3, MMP10, and MMP12. Several species with metalloproteinase activity were characterized and found to be related to each other. The results indicate that an MMP pro-enzyme of >/=200 kDa was released from the CHO cells during the production phase. The enzyme expressed collagenase/gelatinase activity when activated. Due to autoproteolysis, a number of smaller, less specific MMPs were formed with the smallest form, a 19.4 kDa protein, being the most active. These results may be of particular relevance for other production processes using CHO cells for the expression of recombinant proteins.

CHARACTERIZATION OF A NOVEL METALLOPROTEINASE IN DUVERNOY'S GLAND OF RHABDOPHIS TIGRINUS TIGRINUS

During the characterization of hemorrhagic factor in venom of Rhabdophis tigrinus tigrinus, so-called Yamakagashi in Japan, one of the Colubridae family, a novel metalloproteinase with molecular weight of 38 kDa in the Duvernoy's gland of Yamakagashi was identified by gelatin zymography and by monitoring its proteolytic activity using a fluorescence peptide substrate, MOCAc-PLGLA2pr(Dnp)AR-NH2, which was developed for measuring the well-known matrix metalloproteinase (MMP) activity. After purification by gel filtration HPLC and/or column switch HPLC system consisting of an affinity column, which was immobilized with a synthetic BS-10 peptide (MQKPRCGVPD) originating from propeptide domain of MMP-7 and a reversed-phase column, the N-terminal amino acid sequence of the 38 kDa metalloproteinase was identified as FNTFPGDLK which shared a high homology to Xenopus MMP-9. The 38 kDa metalloproteinase required Zn2+ and Ca2+ ions for its proteolytic activity. In addition, the proteolytic activity was almost completely inhibited by BS-10, a MMP inhibitor, but not by the serine proteinase inhibitors, cysteine proteinase inhibitors and aspartic proteinase inhibitors. Together these results demonstrated that the 38 kDa proteinase is a novel snake verom metalloproteinase (SVMP) containing HExGHxxGxxH motif which possesses high affinity to the BS-10 peptide, into its molecule, and the enzymatic properties are closed to that of MMPs. Based on the results obtained in the present study, we concluded that the 38 kDa metalloproteinase is a novel metalloproteinase whose activity may be regulated by the cysteine switch mechanism, and could be classified as one of the matrix metalloproteinases rather than snake venom metalloproteinases.

Filter sterilization of highly infectious samples to prevent false negative analysis of matrix metalloproteinase activity

Matrix metalloproteinases (MMPs) are implicated in the immunopathology of numerous infectious diseases. High risk samples such as those generated after infection with Mycobacterium tuberculosis require filter sterilization for safe analysis of MMP concentrations. Here, we report that commercial filter membranes may cause artefacts by binding MMPs. Anopore 0.2 microM membrane filtration reduced MMP-1 concentrations to undetectable levels by zymography and Western blotting. Polypropylene 0.45 microM filtration removed some MMP-1, while Polysulphone, Durapore and Bio-inert 0.2 microM membranes did not remove MMP-1. Anopore filtration also removed all MMP-7 and -9 activity, suggesting that the conserved MMP catalytic domain binds the membrane. This study demonstrates the importance of selecting the appropriate filter in MMP analysis to avoid incorrectly excluding MMP involvement in infection-related immunopathology.

Matrix metalloproteinase-26 is associated with estrogen-dependent malignancies and targets alpha1-antitrypsin serpin

Proteases exert control over cell behavior and affect many biological processes by making proteolytic modification of regulatory proteins. The purpose of this paper is to describe novel, important functions of matrix metalloproteinase (MMP)-26. alpha1-Antitrypsin (AAT) is a serpin, the primary function of which is to regulate the activity of neutrophil/leukocyte elastase. Insufficient antiprotease activity because of AAT deficiency in the lungs is a contributing factor to early-onset emphysema. We recently discovered that AAT is efficiently cleaved by a novel metalloproteinase, MMP-26, which exhibits an unconventional PH(81)CGVPD Cys switch motif and is autocatalytically activated in cells and tissues. An elevated expression of MMP-26 in macrophages and polymorphonuclear leukocytes supports the functional role of MMP-26 in the AAT cleavage and inflammation. We have demonstrated a direct functional link of MMP-26 expression with an estrogen dependency and confirmed the presence of the estrogen-response element in the MMP-26 promoter. Immunostaining of tumor cell lines and biopsy specimen microarrays confirmed the existence of the inverse correlations of MMP-26 and AAT in cells/tissues. An expression of MMP-26 in the estrogen-dependent neoplasms is likely to contribute to the inactivation of AAT, to the follow-up liberation of the Ser protease activity, and because of these biochemical events, to promote matrix destruction and malignant progression. In summary, we hypothesize that MMP-26, by cleaving and inactivating the AAT serpin, operates as a unique functional link that regulates a coordinated interplay between Ser and metalloproteinases in estrogen-dependent neoplasms.

Three small integrin‐binding ligand N‐linked glycoproteins (SIBLINGs) bind and activate specific matrix metalloproteinases

Matrix metalloproteinases (MMPs) are critical for development, wound healing, and for the progression of cancer. It is generally accepted that MMPs are secreted in a latent form (proMMP) and are activated only upon removal of their inhibitory propeptides. This report shows that three members of the SIBLING (Small, Integrin-Binding LIgand, N-linked Glycoprotein) family can specifically bind (Kd approximately equal nM) and activate three different MMPs. Binding of SIBLING to their corresponding proMMPs is associated with structural changes as indicated by quenching of intrinsic tryptophan fluorescence, increased susceptibility to plasmin cleavage, and decreased inhibition by specific natural and synthetic inhibitors. Activation includes both making the proMMPs enzymatically active and the reactivation of the TIMP (tissue inhibitors of MMP) inhibited MMPs. Bone sialoprotein specifically binds proMMP-2 and active MMP-2, while osteopontin binds proMMP-3 and active MMP-3, and dentin matrix protein-1 binds proMMP-9 and active MMP-9. Both pro and active MMP-SIBLING complexes are disrupted by the abundant serum protein, complement Factor H, thereby probably limiting SIBLING-mediated activation to regions immediately adjacent to sites of secretion in vivo. These data suggest that the SIBLING family offers an alternative method of controlling the activity of at least three MMPs.

Direct activation of pro-matrix metalloproteinase-2 by leukolysin/membrane-type 6 matrix metalloproteinase/matrix metalloproteinase 25 at the asn(109)-Tyr bond

Leukolysin/membrane-type 6 matrix metalloproteinase (leukolysin/MT6-MMP), a glycosylphosphatidylinositol-anchored neutrophil matrix metalloproteinase, is also abnormally expressed in brain cancer tissues. Yet, little is known about its role in cancer progression. Here we show that MT6-MMP is capable of activating proMMP-2, an enzyme implicated in tumor invasion and metastasis. Although MT6-MMP is only 10% as active as MT5-MMP in mediating proMMP-2 activation, it generates a higher ratio of mature/intermediate forms of MMP-2 than MT5-MMP. Consistently, purified CAT of MT6-MMP converts proMMP-2 into mostly the mature form. Using the catalytically inactive mutant MMP-2EA (the E404A mutant of proMMP-2), which cannot autocatalytically mature from the intermediate form into the mature one, we show that MT6-MMP cleaves not only the known MT-MMP-processing site at Asn(66)-Leu but also the previously unsuspected Asn(109)-Tyr to yield a fully mature molecule. Despite their difference in mediating proMMP-2 activation in transfected cells, the CAT of MT6-MMP appears to be as efficient as that of MT5-MMP in cleaving proMMP-2EA in buffer, suggesting that its CAT is a strong proMMP-2 activator. Indeed, the CAT of MT6-MMP can partially substitute the CAT of prototypical MT1-MMP in mediating proMMP-2 activation. Taken these facts together, we conclude that MT6-MMP may participate in tumor invasion and metastasis by directly converting proMMP-2 into active form.

Extracellular metalloproteinase activity in Phytomonas françai

Extracellular proteolytic activities were detected in Phytomonas françai culture supernatant. A 67-kDa enzyme was purified by ammonium sulfate precipitation and gel filtration in a HPLC system. This proteinase was optimally active at 28 degrees C and pH 5.0; and the use of proteolytic inhibitors indicated that it belongs to the metalloproteinase class. This is the first report on the purification of an extracellular metalloproteinase from a Phytomonas species.

Molecular mechanism involved in matrix dependent upregulation of matrix metalloproteinases in monocyte/macrophage

Production of macrophage specific matrix metalloproteinases (MMPs) by monocyte/macrophage (mo/mphi) maintained in vitro on matrix protein substrata has been examined to study the mechanism of matrix protein dependent upregulation of macrophage specific activity. Using specific blocking reagents we have found that interaction of peripheral blood mononuclear cells (PBMC) with extracellular matrix components is crucial for its differentiation to macrophages. Multiwell zymography has shown that production of MMPs was significantly inhibited in cells maintained on fibronectin (FN) pretreated with antibodies to alpha(5), beta(1) integrins and synthetic peptide RGDS. Further, quantification by ELISA showed a significant inhibition in MMP production in cells pretreated with these blocking reagents. Genistein, a non-specific inhibitor of tyrosine kinases, significantly reduced production of MMPs in cells maintained on FN and collagen type IV (COL IV). Immunoblotting analysis has shown that tyrosine phosphorylation occurs in 30 min and two proteins of approximately 115 and approximately 72 kDa are being phosphorylated upon PBMC-FN interaction. These results indicate that integrin mediated downstream signalling involving tyrosine phosphorylation is required for mediating intracellular events associated with differentiation of monocytes to macrophages.

Matrix metalloproteinases induction by pseudomonal virulence factors and inflammatory cytokines in vitro

The pathogenesis of pseudomonal keratitis was investigated by focusing on induction and activation of matrix metalloproteinases (MMPs) by pseudomonal virulence factors and proinflammatory cytokines. Corneal lesions and MMP induction in vivo were evaluated in rabbit corneas infected with a clinical isolate of Pseudomonas aeruginosa. Effects of pseudomonal virulence factors [elastase, alkaline protease, exotoxin A and lipopolysaccharide (LPS)], tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta on MMP induction and activation were further examined in vitro in rabbit corneal fibroblasts (RCF) and human fibrosarcoma (HT1080) cells using reverse transcriptase-polymerase chain reaction (RT-PCR), zymography and immunoblotting. Corneal ulcers with typical ring abscesses were observed 12-24 h after infection, and MMPs, particularly MMP-9, were upregulated in infected corneas. Pseudomonal elastase caused the most extensive damage to both cell types. RCF treated with pseudomonal exoproteases or LPS expressed and secreted MMP-9. Exotoxin A had no effect on MMP expression. Both IL-1beta and TNF-alpha augmented MMP-9 expression in HT1080 cells. Pseudomonal elastase proteolytically activated MMP-2 and MMP-9 released from the cells. In conclusion, corneal destruction seen with P. aeruginosa infections may result from enhanced expression of MMPs by corneal stromal cells stimulated with pseudomonal exoproteases and proinflammatory cytokines and the proteolytic activation of MMPs by pseudomonal elastase.

Expression of a novel matrix metalloproteinase gene during Cynops early embryogenesis

Matrix metalloproteinases (MMPs) are thought to play important roles in the gastrulation of Cynops pyrrhogaster embryos. MMP cDNAs were cloned from Cynops pyrrhogaster and we report here a novel MMP called CyMMP, which has strong similarity to MMP-21 (XMMP) in Xenopus. Reverse transcription-polymerase chain reaction (RT-PCR) analysis demonstrated that CyMMP mRNA was already present in cleavage stage embryos. The amount of the mRNA then gradually decreased, but increased again starting in late gastrula. There were regional differences in the level of CyMMP mRNA expression at late gastrula: the involved archenteron roof was the predominant site of expression of the gene, while there was weak expression in the neuroectoderm and epidermal ectoderm. We also found that the gene was activated in artificially mesodermalized ectoderm. The present findings indicate that CyMMP mRNA expression is activated in differentiating mesoderm during gastrulation, suggesting that CyMMP plays a role in gastrulation-related cell movement.

A matrix metalloproteinase gene is expressed at the boundary of senescence and programmed cell death in cucumber

Cell-cell and extracellular cell matrix (ECM) interactions provide cells with information essential for controlling morphogenesis, cell-fate specification, and cell death. In animals, one of the major groups of enzymes that degrade the ECM is the matrix metalloproteinases (MMPs). Here, we report the characterization of the cucumber (Cucumis sativus L. cv Marketmore) Cs1-MMP gene encoding such an enzyme likely to play a role in plant ECM degradation. Cs1-MMP has all the hallmark motif characteristics of animal MMPs and is a pre-pro-enzyme having a signal peptide, propeptide, and zinc-binding catalytic domains. Cs1-MMP also displays functional similarities with animal MMPs. For example, it has a collagenase-like activity that can cleave synthetic peptides and type-I collagen, a major component of animal ECM. Cs1-MMP activity is completely inhibited by a hydroxamate-based inhibitor that binds at the active site of MMPs in a stereospecific manner. The Cs1-MMP gene is expressed de novo at the end stage of developmental senescence, prior to the appearance of DNA laddering in cucumber cotyledons leaf discs and male flowers. As the steady-state level of Cs1-MMP mRNA peaks late in senescence and the pro-enzyme must undergo maturation and activation, the protease is probably not involved in nutrient remobilization during senescence but may have another function. The physiological substrates for Cs1-MMP remain to be determined, but the enzyme represents a good candidate for plant ECM degradation and may be involved in programmed cell death (PCD). Our results suggest that PCD occurs only at the culmination of the senescence program or that the processes are distinct with PCD being triggered at the end of senescence.

Secreted and membrane-associated matrix metalloproteinases of IL-2-activated NK cells and their inhibitors

We have previously documented that rat IL-2-activated NK (A-NK) cells produce matrix metalloproteinase-2 (MMP-2) and MMP-9. In this study, we describe mouse A-NK cell-derived MMPs, including MT-MMPs, and also TIMPs. RT-PCR analysis from cDNA of mouse A-NK cells revealed mRNA for MMP-2, MMP-9, MMP-11, MMP-13, MT1-MMP, MT2-MMP, TIMP-1, and TIMP-2. MMP-2 and MMP-9 expression was confirmed by gelatin zymography. Moreover, we report for the first time that MT-MMPs are expressed by NK cells, i.e., large granular lymphocytes as determined by both RT-PCR and Western blots. TIMP-1 expression was detected as a 29-kDa protein in Western blots. It is intriguing that TIMP-2 protein from A-NK cells was also detected as a 29-kDa protein, which is clearly different from the previously reported molecular mass of 21 kDa in mouse and human cells. In addition, inhibition of MMPs by BB-94, a selective inhibitor of MMP, significantly inhibited the ability of mouse A-NK cells to migrate through Matrigel, a model basement membrane. Taken together, these findings suggest that A-NK cells may therefore use multiple MMPs in various cellular functions, including degradation of various extracellular matrix molecules as they extravasate from blood vessels and accumulate within cancer metastases following their adoptive transfer.

Proteinases in developing dental enamel

For almost three decades, proteinases have been known to reside within developing dental enamel. However, identification and characterization of these proteinases have been slow and difficult, because they are present in very small quantities and they are difficult to purify directly from the mineralizing enamel. Enamel matrix proteins such as amelogenin, ameloblastin, and enamelin are cleaved by proteinases soon after they are secreted, and their cleavage products accumulate in the deeper, more mature enamel layers, while the full-length proteins are observed only at the surface. These results suggest that proteinases are necessary for "activating" enamel proteins so the parent proteins and their cleavage products may perform different functions. A novel matrix metalloproteinase named enamelysin (MMP-20) was recently cloned from tooth tissues and was later shown to localize primarily within the most recently formed enamel. Furthermore, recombinant porcine enamelysin was demonstrated to cleave recombinant porcine amelogenin at virtually all of the sites that have previously been described in vivo. Therefore, enamelysin is at least one enzyme that may be important during early enamel development. As enamel development progresses to the later stages, a profound decrease in the enamel protein content is observed. Proteinases have traditionally been assumed to degrade the organic matrix prior to its removal from the enamel. Recently, a novel serine proteinase named enamel matrix serine proteinase-1 (EMSP1) was cloned from enamel organ epithelia. EMSP1 localizes primarily to the early maturation stage enamel and may, therefore, be involved in the degradation of proteins prior to their removal from the maturing enamel. Other, as yet unidentified, proteinases and proteinase inhibitors are almost certainly present within the forming enamel and await discovery.

Matrix metalloproteinase homologues from Arabidopsis thaliana. Expression and activity

Five genes potentially encoding novel matrix metalloproteinases (MMPs) have been identified on the Arabidopsis thaliana data base. The predicted proteins have a similar domain structure to mammalian MMP-7, with a propeptide and catalytic domain but no C-terminal hemopexin-like domain. Four of the A. thaliana MMPs (At-MMPs) have a predicted C-terminal transmembrane domain. The At-MMPs are differentially expressed in flower, leaf, root, and stem tissues from 14-day-old plants. The cDNA for one of the At-MMPs (At1-MMP) was cloned and expressed in Escherichia coli. Following refolding and purification, the proenzyme At1-MMP was shown to undergo autolytic activation in the presence of an organomercurial with a concomitant decrease in M(r). In contrast to this, trypsin-treatment led to the formation of an inactive product. The activated At1-MMP digested myelin basic protein, but was unable to digest gelatin or casein. Three peptide substrates for MMPs were also cleaved by At1-MMP. The enzyme activity of At1-MMP was inhibited by human tissue inhibitors of metalloproteinases 1 and 2 and the hydroxamate inhibitor BB-94.

Isolation, characterization, and chromosomal location of the mouse enamelysin gene

Mouse enamelysin (Mmp20), a member of the matrix metalloproteinase (MMP) family of extracellular matrix degrading enzymes, shows a high degree of homology with other MMPs, particularly those of the stromelysin/collagenase subfamilies. It is expressed exclusively in ameloblasts and odontoblasts. The mouse enamelysin gene (Mmp20) is made up of 10 exons spanning approximately 65 kb within the MMP gene cluster at the centromeric end of chromosome 9.

Biochemical characterization of the catalytic domain of membrane-type 4 matrix metalloproteinase

A C-terminal truncated form of membrane-type 4 matrix metalloproteinase (MT4-MMP; MMP 17), lacking the hemopexin-like and transmembrane domain, was expressed in Escherichia coli. The catalytic domain was produced by tryptic activation of the recombinant proenzyme and proved to be catalytically active towards the fluorogenic substrate for matrix metalloproteinases (7-methoxycoumarin-4-yl) acetyl-Pro-Leu-Gly-Leu(3-(2,4-dinitrophenyl)-L-2,3-diaminopro-p ionyl)-Ala-Arg-NH2. In contrast to the other three MT-MMPs (MT1-, MT2-, and MT3-MMP), the catalytic domain of MT4-MMP does not activate progelatinase A, nor does it hydrolyze one of the offered extracellular matrix (ECM) proteins, such as collagen types I, II, III, IV, and V, gelatin, fibronectin, laminin or decorin. TIMP-1, a poor inhibitor of MT1-, MT2- and MT3-MMP, suppresses MT4-MMP activity effectively. The progelatinase A/TIMP-2 complex that usually reacts like TIMP-2 also inhibits MT4-MMP. TIMP-2, a strong inhibitor of other MT-MMPS, inhibits MT4-MMP at low concentrations. With increasing TIMP-2 concentration, however, activity passes through a minimum and then increases until at high TIMP-2 concentration the activity is the same as in the absence of TIMP-2. TIMP-1 or the progelatinase A/TIMP-2 complex do not prevent reactivation of MT4-MMP catalytic domain at high TIMP-2 concentrations.