High resolution crystal structure of the catalytic domain of ADAMTS-5 (aggrecanase-2)

Targeting Aggrecanases for Osteoarthritis Therapy: From Zinc Chelation to Exosite Inhibition

Osteoarthritis (OA) is the most common degenerative joint disease. In 1999, two members of the A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTS) family of metalloproteinases, ADAMTS4 and ADAMTS5, or aggrecanases, were identified as the enzymes responsible for aggrecan degradation in cartilage. The first aggrecanase inhibitors targeted the active site by chelation of the catalytic zinc ion. Due to the generally disappointing performance of zinc-chelating inhibitors in preclinical and clinical studies, inhibition strategies tried to move away from the active-site zinc in order to improve selectivity. Exosite inhibitors bind to proteoglycan-binding residues present on the aggrecanase ancillary domains (called exosites). While exosite inhibitors are generally more selective than zinc-chelating inhibitors, they are still far from fulfilling their potential, partly due to a lack of structural and functional data on aggrecanase exosites. Filling this gap will inform the design of novel potent, selective aggrecanase inhibitors.

Selection and characterization of DNA aptamers inhibiting a druggable target of osteoarthritis, ADAMTS-5

There is a critical need for the development of more potent inhibitors for osteoarthritis (OA) therapy given the poor life quality of arthritis patients. Aggrecanase ADAMTS-5 (a disintegrin and metalloproteinase with thrombospondin motifs 5) is an established drug target identified for osteoarthritis. In this study, we evolved and characterized two new DNA aptamer inhibitors of ADAMTS-5, namely apt21 and apt25. The aptamers exhibited nanomolar binding affinity and high specificity against ADAMTS-5. K_D values of apt21 and apt25 were determined by the Enzyme-linked Oligonucleotide Assay (ELONA) at 1.54 ± 0.16 nM and 1.79 ± 0.08 nM, respectively. Circular Dichroism (CD) analysis demonstrated that both aptamers formed monovalent cation dependent G-quadruplex structures. Calcium ions did not affect the binding of the aptamers to ADAMTS-5. The inhibitory effects of apt21 and apt25 on ADAMTS-5 were evaluated by the Förster Resonance Energy Transfer (FRET) assay, in which IC₅₀ values of apt21 and apt25 were estimated at 52.76 ± 6.70 μM and 61.14 ± 9.67 μM, respectively. These two aptamers are the first DNA G-quadruplex aptamers demonstrated to inhibit ADAMTS-5 and could have value for OA therapy.

Diselenide-selenoester ligation in the chemical synthesis of proteins

Peptides and proteins represent an important class of biomolecules responsible for a plethora of structural and functional roles in vivo. Following their translation on the ribosome, the majority of eukaryotic proteins are post-translationally modified, leading to a proteome that is much larger than the number of genes present in a given organism. In order to understand the functional role of a given protein modification, it is necessary to access peptides and proteins bearing homogeneous and site-specific modifications. Accordingly, there has been significant research effort centered on the development of peptide ligation methodologies for the chemical synthesis of modified proteins. In this chapter we outline the discovery and development of a contemporary methodology called the diselenide-selenoester ligation (DSL) that enables the rapid and efficient fusion of peptide fragments to generate synthetic proteins. The practical aspects of using DSL for the preparation of chemically modified peptides and proteins in the laboratory is described. In addition, recent advances in the application of the methodology are outlined, exemplified by the synthesis and biological evaluation of a number of complex protein targets.

Computational insights into the substrate recognition mechanism of cartilage extracellular matrix degradation

Articular cartilage is connective tissue that forms a slippery load-bearing joint surface between bones. With outstanding mechanical properties, it plays an essential role in cushioning impact and protecting the ends of bones. Abnormal mechanical stimulation, such as repetitive overloading or chondral injury, induces excessive cartilage extracellular matrix (ECM) degradation, leading to osteoarthritis and other joint disorders. A disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS-5) is an aggrecanase that dominates the catalysis of aggrecan, the major proteoglycan in the cartilage ECM. Intriguingly, unlike its critical cleavage site Glu373-374Ala, another potential cleavage site, Glu419-420Ala, composed of the same amino acids in the aggrecan interglobular domain, is not a major cleavage site. It remains unclear how ADAMTS-5 distinguishes between them and hydrolyzes the correct scissile bonds. This research introduces a bottom-up in silico approach to reveal the molecular mechanism by which ADAMTS-5 recognizes the cleavage site on aggrecan. It is hypothesized that the sequence in the vicinity assists ADAMTS-5 in positioning the cleavage site. Specific residues were found to serve as binding sites, helping aggrecan bind more stably and fit into the enzyme better. The findings provide insight into the substrate binding and recognition mechanism for cartilage ECM degradation from a brand new atomic-scale perspective, laying the foundation for prophylaxis and treatment of related joint diseases.

Discovery of GLPG1972/S201086, a Potent, Selective, and Orally Bioavailable ADAMTS-5 Inhibitor for the Treatment of Osteoarthritis

There are currently no approved disease-modifying osteoarthritis (OA) drugs (DMOADs). The aggrecanase ADAMTS-5 is key in the degradation of human aggrecan (AGC), a component of cartilage. Therefore, ADAMTS-5 is a promising target for the identification of DMOADs. We describe the discovery of GLPG1972/S201086, a potent and selective ADAMTS-5 inhibitor obtained by optimization of a promising hydantoin series following an HTS. Biochemical activity against rat and human ADAMTS-5 was assessed via a fluorescence-based assay. ADAMTS-5 inhibitory activity was confirmed with human aggrecan using an AGC ELISA. The most promising compounds were selected based on reduction of glycosaminoglycan release after interleukin-1 stimulation in mouse cartilage explants and led to the discovery of GLPG1972/S201086. The anticatabolic activity was confirmed in mouse cartilage explants (IC₅₀ < 1.5 μM). The cocrystal structure of GLPG1972/S201086 with human recombinant ADAMTS-5 is discussed. GLPG1972/S201086 has been investigated in a phase 2 clinical study in patients with knee OA (NCT03595618).

Exosite inhibition of ADAMTS-5 by a glycoconjugated arylsulfonamide

ADAMTS-5 is a major protease involved in the turnover of proteoglycans such as aggrecan and versican. Dysregulated aggrecanase activity of ADAMTS-5 has been directly linked to the etiology of osteoarthritis (OA). For this reason, ADAMTS-5 is a pharmaceutical target for the treatment of OA. ADAMTS-5 shares high structural and functional similarities with ADAMTS-4, which makes the design of selective inhibitors particularly challenging. Here we exploited the ADAMTS-5 binding capacity of β-N-acetyl-d-glucosamine to design a new class of sugar-based arylsulfonamides. Our most promising compound, 4b, is a non-zinc binding ADAMTS-5 inhibitor which showed high selectivity over ADAMTS-4. Docking calculations combined with molecular dynamics simulations demonstrated that 4b is a cross-domain inhibitor that targets the interface of the metalloproteinase and disintegrin-like domains. Furthermore, the interaction between 4b and the ADAMTS-5 Dis domain is mediated by hydrogen bonds between the sugar moiety and two lysine residues (K532 and K533). Targeted mutagenesis of these two residues confirmed their importance both for versicanase activity and inhibitor binding. This positively-charged cluster of ADAMTS-5 represents a previously unknown substrate-binding site (exosite) which is critical for substrate recognition and can therefore be targeted for the development of selective ADAMTS-5 inhibitors.

Crystal structure and substrate-induced activation of ADAMTS13

Platelet recruitment to sites of blood vessel damage is highly dependent upon von Willebrand factor (VWF). VWF platelet-tethering function is proteolytically regulated by the metalloprotease ADAMTS13. Proteolysis depends upon shear-induced conformational changes in VWF that reveal the A2 domain cleavage site. Multiple ADAMTS13 exosite interactions are involved in recognition of the unfolded A2 domain. Here we report through kinetic analyses that, in binding VWF, the ADAMTS13 cysteine-rich and spacer domain exosites bring enzyme and substrate into proximity. Thereafter, binding of the ADAMTS13 disintegrin-like domain exosite to VWF allosterically activates the adjacent metalloprotease domain to facilitate proteolysis. The crystal structure of the ADAMTS13 metalloprotease to spacer domains reveals that the metalloprotease domain exhibits a latent conformation in which the active-site cleft is occluded supporting the requirement for an allosteric change to enable accommodation of the substrate. Our data demonstrate that VWF functions as both the activating cofactor and substrate for ADAMTS13.

High throughput protease profiling comprehensively defines active site specificity for thrombin and ADAMTS13

We have combined random 6 amino acid substrate phage display with high throughput sequencing to comprehensively define the active site specificity of the serine protease thrombin and the metalloprotease ADAMTS13. The substrate motif for thrombin was determined by >6,700 cleaved peptides, and was highly concordant with previous studies. In contrast, ADAMTS13 cleaved only 96 peptides (out of >10⁷ sequences), with no apparent consensus motif. However, when the hexapeptide library was substituted into the P3-P3′ interval of VWF73, an exosite-engaging substrate of ADAMTS13, 1670 unique peptides were cleaved. ADAMTS13 exhibited a general preference for aliphatic amino acids throughout the P3-P3′ interval, except at P2 where Arg was tolerated. The cleaved peptides assembled into a motif dominated by P3 Leu, and bulky aliphatic residues at P1 and P1′. Overall, the P3-P2′ amino acid sequence of von Willebrand Factor appears optimally evolved for ADAMTS13 recognition. These data confirm the critical role of exosite engagement for substrates to gain access to the active site of ADAMTS13, and define the substrate recognition motif for ADAMTS13. Combining substrate phage display with high throughput sequencing is a powerful approach for comprehensively defining the active site specificity of proteases.

Unusual life cycle and impact on microfibril assembly of ADAMTS17, a secreted metalloprotease mutated in genetic eye disease

Secreted metalloproteases have diverse roles in the formation, remodeling, and the destruction of extracellular matrix. Recessive mutations in the secreted metalloprotease ADAMTS17 cause ectopia lentis and short stature in humans with Weill-Marchesani-like syndrome and primary open angle glaucoma and ectopia lentis in dogs. Little is known about this protease or its connection to fibrillin microfibrils, whose major component, fibrillin-1, is genetically associated with ectopia lentis and alterations in height. Fibrillin microfibrils form the ocular zonule and are present in the drainage apparatus of the eye. We show that recombinant ADAMTS17 has unique characteristics and an unusual life cycle. It undergoes rapid autocatalytic processing in trans after its secretion from cells. Secretion of ADAMTS17 requires O-fucosylation and its autocatalytic activity does not depend on propeptide processing by furin. ADAMTS17 binds recombinant fibrillin-2 but not fibrillin-1 and does not cleave either. It colocalizes to fibrillin-1 containing microfibrils in cultured fibroblasts and suppresses fibrillin-2 (FBN2) incorporation in microfibrils, in part by transcriptional downregulation of Fbn2 mRNA expression. RNA in situ hybridization detected Adamts17 expression in specific structures in the eye, skeleton and other organs, where it may regulate the fibrillin isoform composition of microfibrils.

Adamts18 deletion results in distinct developmental defects and provides a model for congenital disorders of lens, lung, and female reproductive tract development

The ADAMTS family comprises 19 secreted metalloproteinases that cleave extracellular matrix components and have diverse functions in numerous disease and physiological contexts. A number of them remain 'orphan' proteases and among them is ADAMTS18, which has been implicated in developmental eye disorders, platelet function and various malignancies. To assess in vivo function of ADAMTS18, we generated a mouse strain with inactivated Adamts18 alleles. In the C57Bl6/Ola background, Adamts18-deficient mice are born in a normal Mendelian ratio, and are viable but show a transient growth delay. Histological examination revealed a 100% penetrant eye defect resulting from leakage of lens material through the lens capsule occurring at embryonic day (E)13.5, when the lens grows rapidly. Adamts18-deficient lungs showed altered bronchiolar branching. Fifty percent of mutant females are infertile because of vaginal obstruction due to either a dorsoventral vaginal septum or imperforate vagina. The incidence of ovarian rete is increased in the mutant mouse strain. Thus, Adamts18 is essential in the development of distinct tissues and the new mouse strain is likely to be useful for investigating ADAMTS18 function in human disease, particularly in the contexts of infertility and carcinogenesis.

Molecular basis for the mechanism of action of an anti-TACE antibody

Inhibitors of tumor necrosis factor-α converting enzyme (TACE) have potential as therapeutics for various diseases. Many small molecule inhibitors, however, exhibit poor specificity profiles because they target the highly conserved catalytic cleft of TACE. We report for the first time the molecular interaction of a highly specific anti-TACE antagonistic antibody (MEDI3622). We characterized the binding of MEDI3622 using mutagenesis, as well as structural modeling and docking approaches. We show that MEDI3622 recognizes a unique surface loop of sIVa-sIVb β-hairpin on TACE M-domain, but does not interact with the conserved catalytic cleft or its nearby regions. The exquisite specificity of MEDI3622 is mediated by this distinct structural feature on the TACE M-domain. These findings may aid the design of antibody therapies against TACE.

ADAM and ADAMTS Family Proteins and Snake Venom Metalloproteinases: A Structural Overview

A disintegrin and metalloproteinase (ADAM) family proteins constitute a major class of membrane-anchored multidomain proteinases that are responsible for the shedding of cell-surface protein ectodomains, including the latent forms of growth factors, cytokines, receptors and other molecules. Snake venom metalloproteinases (SVMPs) are major components in most viper venoms. SVMPs are primarily responsible for hemorrhagic activity and may also interfere with the hemostatic system in envenomed animals. SVMPs are phylogenetically most closely related to ADAMs and, together with ADAMs and related ADAM with thrombospondin motifs (ADAMTS) family proteinases, constitute adamalysins/reprolysins or the M12B clan (MEROPS database) of metalloproteinases. Although the catalytic domain structure is topologically similar to that of other metalloproteinases such as matrix metalloproteinases, the M12B proteinases have a modular structure with multiple non-catalytic ancillary domains that are not found in other proteinases. Notably, crystallographic studies revealed that, in addition to the conserved metalloproteinase domain, M12B members share a hallmark cysteine-rich domain designated as the “ADAM_CR” domain. Despite their name, ADAMTSs lack disintegrin-like structures and instead comprise two ADAM_CR domains. This review highlights the current state of our knowledge on the three-dimensional structures of M12B proteinases, focusing on their unique domains that may collaboratively participate in directing these proteinases to specific substrates.

ADAMTS13 and von Willebrand factor interactions

PURPOSE OF REVIEW

ADAMTS13 is a zinc-containing metalloprotease that cleaves von Willebrand factor (VWF). Deficiency of plasma ADAMTS13 activity is accountable for a potentially fatal blood disorder thrombotic thrombocytopenic purpura (TTP). Understanding of ADAMTS13-VWF interaction is essential for developing novel treatments to this disorder.

RECENT FINDINGS

Despite the proteolytic activity of ADAMTS13 being restricted to the metalloprotease domain, the ancillary proximal C-terminal domains including the disintegrin domain, first TSP-1 repeat, cysteine-rich region, and spacer domain are all required for cleavage of VWF and its analogs. Recent studies have added to our understandings of the role of the specific regions in the disintegrin domain, the cysteine-rich domain, and the spacer domain responsible for its interaction with VWF. Additionally, regulative functions of the distal portion of ADAMTS13 including the TSP-1 2-8 repeats and the CUB domains have been proposed. Finally, fine mapping of anti-ADAMTS13 antibody epitopes have provided further insight into the essential structural elements in ADAMTS13 for VWF binding and the mechanism of autoantibody-mediated TTP.

SUMMARY

Significant progress has been made in our understandings of the structure-function relationship of ADAMTS13 in the past decade. To further investigate ADAMTS13-VWF interactions for medical applications, these interactions must be studied under physiological conditions in vivo.

Anti-ADAMTS5 monoclonal antibodies: implications for aggrecanase inhibition in osteoarthritis

The extracellular matrix of articular cartilage is structurally specialized for efficient absorption of mechanical impact. In particular, giant aggregates of the large chondroitin sulfate proteoglycan, aggrecan, with the glycosaminoglycan, hyaluronan, allow cartilage to resist compressive load. Proteolysis of aggrecan by members of the proteinase family ADAMTS (A disintegrin-like and metalloproteinase domain with thrombospondin type 1 motif), was identified as an early step in the inexorable destruction of cartilage in osteoarthritis (OA). Of the investigated proteinases, ADAMTS5 has emerged as a principal mediator of aggrecan loss in OA, convincingly so in mouse models, and with high probability in humans. ADAMTS5 has a bipartite organization, comprising a proteinase domain and an ancillary domain containing exosites for interaction with aggrecan and other substrates. In a recent issue of this journal, Santamaria et al. characterized anti-ADAMTS5 monoclonal antibodies isolated from a phage display library. By blocking the catalytic site of the ADAMTS5 immunogen with a synthetic inhibitor, the authors of the paper biased selection of antibodies to the ancillary domain. This work, together with other antibodies targeting ADAMTS5, offers diverse, high-affinity and, as far as can be determined, selective aggrecanase inhibitors. Mapping of their epitopes provided novel insights into ADAMTS5 interactions with aggrecan. These monoclonal antibodies deserve continued investigation for potential arthritis therapy, although their successful use will require a comprehensive understanding of the physiological roles of ADAMTS5, and its regulation, intrinsic properties and intermolecular interactions.

Classification of ADAMTS binding sites: The first step toward selective ADAMTS7 inhibitors

Genome-wide association studies identified ADAMTS7 as a risk locus for coronary artery disease. In carotid arteries of rats, neointima formation after balloon-mediated injury goes along with enhanced Adamts7 expression. Vice versa, Adamts7-deficient mice display reduced neointima formation following vascular injury. Although a causal link between ADAMTS7 and coronary artery disease remains to be proven, inhibition of ADAMTS7 represents a potential new target for intervention in this disease. ADAMTS7, a member of the 'a disintegrin and metalloproteinase with thrombospondin motifs' (ADAMTS) family of proteins, contains a catalytic zinc ion in the binding site of its metalloproteinase domain. The structure of ADAMTS7 and its inhibitors are unknown. In this study, we used in silico methods, including homology modeling and pharmacophore modeling, to analyze the ADAMTS7 metalloproteinase domain, particularly its binding site. The results revealed structural and sequence differences relative to the binding sites of the other ADAMTS proteins; these non-conserved regions represent potential binding regions for selective ADAMTS7 inhibitors. The main contribution of this study is the proposal of a pharmacophore for ADAMTS7. The characterization of the ADAMTS7 binding site and definition of a pharmacophore are the first step toward developing a new therapeutic target for coronary artery disease.

Linker regions and flexibility around the metalloprotease domain account for conformational activation of ADAMTS-13

BACKGROUND

Recently, conformational activation of ADAMTS-13 was identified. This mechanism showed the evolution from a condensed conformation, in which the proximal MDTCS and distal T2-CUB2 domains are in close contact with each other, to an activated, open structure due to binding with von Willebrand factor (VWF).

OBJECTIVES

Identification of cryptic epitope/exosite exposure after conformational activation and of sites of flexibility in ADAMTS-13.

METHODS

The activating effect of 25 anti-T2-CUB2 antibodies was studied in the FRETS-VWF73 and the vortex assay. Cryptic epitope/exosite exposure was determined with ELISA and VWF binding assay. The molecular basis for flexibility was hypothesized through rapid automatic detection and alignment of repeats (RADAR) analysis, tested with ELISA using deletion variants and visualized using electron microscopy.

RESULTS

Eleven activating anti-ADAMTS-13 antibodies, directed against the T5-CUB2 domains, were identified in the FRETS-VWF73 assay. RADAR analysis identified three linker regions in the distal domains. Interestingly, identification of an antibody recognizing a cryptic epitope in the metalloprotease domain confirmed the contribution of these linker regions to conformational activation of the enzyme. The proof of flexibility around both the T2 and metalloprotease domains, as shown by by electron microscopy, further supported this contribution. In addition, cryptic epitope exposure was identified in the distal domains, because activating anti-T2-CUB2 antibodies increased the binding to folded VWF up to ~3-fold.

CONCLUSION

Conformational activation of ADAMTS-13 leads to cryptic epitope/exosite exposure in both proximal and distal domains, subsequently inducing increased activity. Furthermore, three linker regions in the distal domains are responsible for flexibility and enable the interaction between the proximal and the T8-CUB2 domains.

Inhibition of aggrecanases as a therapeutic strategy in osteoarthritis

Over the last decade, there has been a large effort to target aggrecanases, which are responsible for the degradation of the aggrecan in the extracellular matrix of joints, in order to hopefully lead to new treatments for osteoarthritis. Only a few inhibitors have been effective in explants or rodent models and thus only a few have reached the clinic, none of which have proven to be effective. In this article, a survey of chemical series is described, covering historical and recent inhibitors and highlighting how some of their problems were resolved, with a critical overview of the challenges encountered. A large effort should be undertaken in designing smaller compounds with higher residence times, defining new interaction sites on the aggrecanases and exploiting target flexibility.

The D173G mutation in ADAMTS-13 causes a severe form of congenital thrombotic thrombocytopenic purpura. A clinical, biochemical and in silico study

Congenital thrombotic thrombocytopenic purpura (TTP) is a rare form of thrombotic microangiopathy, inherited with autosomal recessive mode as a dysfunction or severe deficiency of ADAMTS-13 (A Disintegrin And Metalloprotease with ThromboSpondin 1 repeats Nr. 13), caused by mutations in the ADAMTS-13 gene. About 100 mutations of the ADAMTS-13 gene were identified so far, although only a few characterised by in vitro expression studies. A new Asp to Gly homozygous mutation at position 173 of ADAMTS-13 sequence was identified in a family of Romanian origin, with some members affected by clinical signs of TTP. In two male sons, this mutation caused a severe (< 3%) deficiency of ADAMTS-13 activity and antigen level, associated with periodic thrombocytopenia, haemolytic anaemia and mild mental confusion. Both parents, who are cousins, showed the same mutation in heterozygous form. Expression studies of the mutant ADAMTS-13, performed in HEK293 cells, showed a severe decrease of the enzyme's activity and secretion, although the protease was detected inside the cells. Molecular dynamics found that in the D173G mutant the interface area between the metalloprotease domain and the disintegrin-like domain significantly decreases during the simulations, while the proline-rich 20 residues linker region (LR, 285-304) between them undergoes extensive conformational changes. Inter-domain contacts are also significantly less conserved in the mutant compared to the wild-type. Both a decrease of the inter-domain contacts along with a substantial conformational rearrangement of LR interfere with the proper maturation and folding of the mutant ADAMTS-13, thus impairing its secretion.

Insights on ADAMTS proteases and ADAMTS-like proteins from mammalian genetics

The mammalian ADAMTS superfamily comprises 19 secreted metalloproteinases and 7 ADAMTS-like proteins, each the product of a distinct gene. Thus far, all appear to be relevant to extracellular matrix function or to cell-matrix interactions. Most ADAMTS functions first emerged from analysis of spontaneous human and animal mutations and genetically engineered animals. The clinical manifestations of Mendelian disorders resulting from mutations in ADAMTS2, ADAMTS10, ADAMTS13, ADAMTS17, ADAMTSL2 and ADAMTSL4 identified essential roles for each gene, but also suggested potential cooperative functions of ADAMTS proteins. These observations were extended by analysis of spontaneous animal mutations, such as in bovine ADAMTS2, canine ADAMTS10, ADAMTS17 and ADAMTSL2 and mouse ADAMTS20. These human and animal disorders are recessive and their manifestations appear to result from a loss-of-function mechanism. Genome-wide analyses have determined an association of some ADAMTS loci such as ADAMTS9 and ADAMTS7, with specific traits and acquired disorders. Analysis of genetically engineered rodent mutations, now achieved for over half the superfamily, has provided novel biological insights and animal models for the respective human genetic disorders and suggested potential candidate genes for related human phenotypes. Engineered mouse mutants have been interbred to generate combinatorial mutants, uncovering cooperative functions of ADAMTS proteins in morphogenesis. Specific genetic models have provided crucial insights on mechanisms of osteoarthritis (OA), a common adult-onset degenerative condition. Engineered mutants will facilitate interpretation of exome variants identified in isolated birth defects and rare genetic conditions, as well as in genome-wide screens for trait and disease associations. Mammalian forward and reverse genetics, together with genome-wide analysis, together constitute a powerful force for revealing the functions of ADAMTS proteins in physiological pathways and health disorders. Their continuing use, together with genome-editing technology and the ability to generate stem cells from mutants, presents numerous opportunities for advancing basic knowledge, human disease pathways and therapy.

Genetically Engineered Mouse Models Reveal the Importance of Proteases as Osteoarthritis Drug Targets

More than two decades of research has revealed a combination of proteases that determine cartilage degradation in osteoarthritis. These include metalloproteinases, which degrade the major macromolecules in cartilage, aggrecan and type II collagen, serine proteases, and cysteine proteases, for example cathepsin K. This review summarizes the function of proteases in osteoarthritis progression, as revealed by studies of genetically engineered mouse models. A brief overview of the biochemical characteristics and features of several important proteases is provided, with the objective of increasing understanding of their function. Published data reveal at least three enzymes to be major targets for osteoarthritis drug development: ADAMTS-5, MMP-13, and cathepsin K. In surgical models of osteoarthritis, mice lacking these enzymes are protected from cartilage damage and, to varying degrees, from bone changes. In-vivo studies targeting these proteases with selective small-molecule inhibitors have been performed for a variety of animal models. Mouse models will provide opportunities for future tests of the therapeutic effect of protease inhibitors, both on progression of structural damage to the joint and on associated pain.

Arylsulfonamide inhibitors of aggrecanases as potential therapeutic agents for osteoarthritis: synthesis and biological evaluation

Aggrecanases, in particular aggrecanase-2 (ADAMTS-5), are considered the principal proteases responsible for aggrecan degradation in osteoarthritis. For this reason, considerable effort has been put on the discovery and development of aggrecanase inhibitors able to slow down or halt the progression of osteoarthritis. We report herein the synthesis and biological evaluation of a series of arylsulfonamido-based hydroxamates as aggrecanase inhibitors. Compound 18 was found to have a nanomolar activity for ADAMTS-5, ADAMTS-4 and MMP-13 and high selectivity over MMP-1 and MMP-14. Furthermore, this compound proved to be effective in blocking ex vivo cartilage degradation without having effect on cell cytotoxicity.

Emerging Roles of ADAMTSs in Angiogenesis and Cancer

A Disintegrin-like And Metalloproteinase with ThromboSpondin motifs—ADAMTSs—are a multi-domain, secreted, extracellular zinc metalloproteinase family with 19 members in humans. These extracellular metalloproteinases are known to cleave a wide range of substrates in the extracellular matrix. They have been implicated in various physiological processes, such as extracellular matrix turnover, melanoblast development, interdigital web regression, blood coagulation, ovulation, etc. ADAMTSs are also critical in pathological processes such as arthritis, atherosclerosis, cancer, angiogenesis, wound healing, etc. In the past few years, there has been an explosion of reports concerning the role of ADAMTS family members in angiogenesis and cancer. To date, 10 out of the 19 members have been demonstrated to be involved in regulating angiogenesis and/or cancer. The mechanism involved in their regulation of angiogenesis or cancer differs among different members. Both angiogenesis-dependent and -independent regulation of cancer have been reported. This review summarizes our current understanding on the roles of ADAMTS in angiogenesis and cancer and highlights their implications in cancer therapeutic development.

Identification of epitopes on ADAMTS13 recognized by a panel of monoclonal antibodies with functional or non-functional effects on catalytic activity

INTRODUCTION

von Willebrand factor (VWF) cleavage by ADAMTS13 is mediated by multi-step interactions between their multi-domain structures. To clarify the relationship between inhibitory effects of monoclonal antibodies and epitopes on each ADAMTS13 domain, we analyzed how each ADAMTS13 domain contributes to catalyze VWF using a mouse anti-ADAMTS13 monoclonal antibody panel.

MATERIALS AND METHODS

FRETS-VWF73 assay was used to examine the effects of 14 anti-ADAMTS13 monoclonal antibodies on the catalytic activity of plasma ADAMTS13. Epitope mapping was performed using phage surface display. Libraries expressing peptide fragments of ADAMTS13 were screened with the monoclonal antibodies.

RESULTS

Eleven epitopes of 14 monoclonal antibodies were successfully defined. Three monoclonal antibodies recognizing metalloprotease or disintegrin-like domains strongly inhibited the catalytic activity and their epitopes were on Gln159-Asp166, Tyr 305-Glu327, and Asn308-Glu376. Five monoclonal antibodies recognizing TSP1-3 to -7 repeats showed weak inhibitory effects, and their epitopes were on Pro744-Ala806, Pro856-Cys864, Gln892-Gly940, Cys1007-Cys1072, and Gln1163-Asn1185. Four monoclonal antibodies recognizing the TSP1-1, TSP1-2, CUB1 or CUB2 domains had no inhibitory effects, and their epitopes, except that for TSP1-1, were Pro682-Cys742, Thr1200-Cys1213, and Gln1409-Glu1414. Two monoclonal antibodies recognizing cysteine-rich and spacer domains showed moderate inhibitory effects, but their epitopes were not determined.

CONCLUSIONS

We revealed the epitopes of 11 monoclonal anti-ADAMTS13 antibodies on each of the domains and clarified their association with inhibitory effects on VWF catalysis under static conditions. Catalytic activity correlated strongly with the epitopes on metalloprotease and disintegrin-like domains, weakly with those on TSP1-3 to -7 repeats, and negatively with those on TSP1-1, -2, and CUB domains.

Structure of human ADAM-8 catalytic domain complexed with batimastat

The role of ADAM-8 in cancer and inflammatory diseases such as allergy, arthritis and asthma makes it an attractive target for drug development. Therefore, the catalytic domain of human ADAM-8 was expressed, purified and crystallized in complex with a hydroxamic acid inhibitor, batimastat. The crystal structure of the enzyme-inhibitor complex was refined to 2.1 Å resolution. ADAM-8 has an overall fold similar to those of other ADAM members, including a central five-stranded β-sheet and a catalytic Zn(2+) ion. However, unique differences within the S1' binding loop of ADAM-8 are observed which might be exploited to confer specificity and selectivity to ADAM-8 competitive inhibitors for the treatment of diseases involving this enzyme.

Genetic and functional linkage between ADAMTS superfamily proteins and fibrillin-1: a novel mechanism influencing microfibril assembly and function

Tissue microfibrils contain fibrillin-1 as a major constituent. Microfibrils regulate bioavailability of TGFβ superfamily growth factors and are structurally crucial in the ocular zonule. FBN1 mutations typically cause the Marfan syndrome, an autosomal dominant disorder manifesting with skeletal overgrowth, aortic aneurysm, and lens dislocation (ectopia lentis). Infrequently, FBN1 mutations cause dominantly inherited Weill-Marchesani syndrome (WMS), isolated ectopia lentis (IEL), or the fibrotic condition, geleophysic dysplasia (GD). Intriguingly, mutations in ADAMTS [a disintegrin-like and metalloprotease (reprolysin-type) with thrombospondin type 1 motif] family members phenocopy these disorders, leading to recessive WMS (ADAMTS10), WMS-like syndrome (ADAMTS17), IEL (ADAMTSL4 and ADAMTS17) and GD (ADAMTSL2). An ADAMTSL2 founder mutation causes Musladin-Lueke syndrome, a fibrotic disorder in beagle dogs. The overlapping disease spectra resulting from fibrillin-1 and ADAMTS mutations, interaction of ADAMTS10 and ADAMTSL2 with fibrillin-1, and evidence that these ADAMTS proteins accelerate microfibril biogenesis, constitutes a consilience suggesting that some ADAMTS proteins evolved to provide a novel mechanism regulating microfibril formation and consequently cell behavior.

Proteoglycan degradation by the ADAMTS family of proteinases

Proteoglycans are key components of extracellular matrices, providing structural support as well as influencing cellular behaviour in physiological and pathological processes. The diversity of proteoglycan function reported in the literature is equally matched by diversity in proteoglycan structure. Members of the ADAMTS (A Disintegrin And Metalloproteinase with ThromboSpondin motifs) family of enzymes degrade proteoglycans and thereby have the potential to alter tissue architecture and regulate cellular function. In this review, we focus on ADAMTS enzymes that degrade the lectican and small leucine-rich repeat families of proteoglycans. We discuss the known ADAMTS cleavage sites and the consequences of cleavage at these sites. We illustrate our discussion with examples from the literature in which ADAMTS proteolysis of proteoglycans makes profound changes to tissue function.

Structure analysis reveals the flexibility of the ADAMTS-5 active site

A ((1S,2R)-2-hydroxy-2,3-dihydro-1H-inden-1-yl) succinamide derivative (here referred to as Compound 12) shows significant activity toward many matrix metalloproteinases (MMPs), including MMP-2, MMP-8, MMP-9, and MMP-13. Modeling studies had predicted that this compound would not bind to ADAMTS-5 (a disintegrin and metalloproteinase with thrombospondin motifs-5) due to its shallow S1' pocket. However, inhibition analysis revealed it to be a nanomolar inhibitor of both ADAMTS-4 and -5. The observed inconsistency was explained by analysis of crystallographic structures, which showed that Compound 12 in complex with the catalytic domain of ADAMTS-5 (cataTS5) exhibits an unusual conformation in the S1' pocket of the protein. This first demonstration that cataTS5 can undergo an induced conformational change in its active site pocket by a molecule like Compound 12 should enable the design of new aggrecanase inhibitors with better potency and selectivity profiles.

Unraveling the scissile bond: how ADAMTS13 recognizes and cleaves von Willebrand factor

von Willebrand factor (VWF) is a large adhesive glycoprotein with established functions in hemostasis. It serves as a carrier for factor VIII and acts as a vascular damage sensor by attracting platelets to sites of vessel injury. VWF size is important for this latter function, with larger multimers being more hemostatically active. Functional imbalance in multimer size can variously cause microvascular thrombosis or bleeding. The regulation of VWF multimeric size and platelet-tethering function is carried out by ADAMTS13, a plasma metalloprotease that is constitutively active. Unusually, protease activity of ADAMTS13 is controlled not by natural inhibitors but by conformational changes in its substrate, which are induced when VWF is subject to elevated rheologic shear forces. This transforms VWF from a globular to an elongated protein. This conformational transformation unfolds the VWF A2 domain and reveals cryptic exosites as well as the scissile bond. To enable VWF proteolysis, ADAMTS13 makes multiple interactions that bring the protease to the substrate and position it to engage with the cleavage site as this becomes exposed by shear. This article reviews recent literature on the interaction between these 2 multidomain proteins and provides a summary model to explain proteolytic regulation of VWF by ADAMTS13.

Mechanism of von Willebrand factor scissile bond cleavage by a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13)

The platelet-tethering function of von Willebrand factor (VWF) is proteolytically regulated by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), which cleaves the Tyr1605-Met1606 (P1-P1') bond in the VWF A2 domain. To date, most of the functional interactions between ADAMTS13 and VWF that have been characterized involve VWF residues that are C terminal to the scissile bond. We now demonstrate that the substrate P3 position in VWF, Leu1603, is a critical determinant of VWF proteolysis. When VWF Leu1603 was substituted with Ser, Ala, Asn, or Lys in a short VWF substrate, VWF115, proteolysis was either greatly reduced or ablated (up to 400-fold reduction in k(cat)/K(m)). As Leu1603 must interact with residues proximate to the Zn(2+) ion coordinated in the active center of ADAMTS13, we sought the corresponding S3 interacting residues. Substitution of 10 candidate residues in the metalloprotease domain of ADAMTS13 identified two spatially separated clusters centered on Leu198 or Val195 (acting with Leu232 and Leu274, or with Leu151, respectively), as possible subsites interacting with VWF. These experimental findings using the short VWF115 substrate were replicated using full-length VWF. It is hypothesized that VWF Leu1603 interacts with ADAMTS13 Leu198/Leu232/Leu274 and that Val195/Leu151 may form part of a S1 subsite. The recognition of VWF Leu1603 by ADAMTS13, in conjunction with previously reported remote exosites C terminal of the cleavage site, suggests a mechanism whereby the VWF P1-P1' scissile bond is brought into position over the active site for cleavage. Together with recently characterized remote exosite interactions, these findings provide a general framework for understanding the ADAMTS family substrate interactions.

Snake venom metalloproteinases: structure, function and relevance to the mammalian ADAM/ADAMTS family proteins

Metalloproteinases are among the most abundant toxins in many Viperidae venoms. Snake venom metalloproteinases (SVMPs) are the primary factors responsible for hemorrhage and may also interfere with the hemostatic system, thus facilitating loss of blood from the vasculature of the prey. SVMPs are phylogenetically most closely related to mammalian ADAM (a disintegrin and metalloproteinase) and ADAMTS (ADAM with thrombospondin type-1 motif) family of proteins and, together with them, constitute the M12B clan of metalloendopeptidases. Large SVMPs, referred to as the P-III class of SVMPs, have a modular architecture with multiple non-catalytic domains. The P-III SVMPs are characterized by higher hemorrhagic and more diverse biological activities than the P-I class of SVMPs, which only have a catalytic domain. Recent crystallographic studies of P-III SVMPs and their mammalian counterparts shed new light on structure-function properties of this class of enzymes. The present review will highlight these structures, particularly the non-catalytic ancillary domains of P-III SVMPs and ADAMs that may target the enzymes to specific substrates. This article is part of a Special Issue entitled: Proteolysis 50years after the discovery of lysosome.

Using fluorogenic peptide substrates to assay matrix metalloproteinases

A continuous assay method, such as the one that utilizes an increase in fluorescence upon hydrolysis, allows for rapid and convenient kinetic evaluation of proteases. To better understand MMP behaviors and to aid in the design of MMP inhibitors, a variety of sequence specificity, phage display, and combinatorial chemistry studies have been performed. Results of these studies have been valuable for defining the differences in MMPs and for creating quenched fluorescent substrates that utilize fluorescence resonance energy transfer (FRET)/intramolecular fluorescence energy transfer (IFET). FRET triple-helical substrates have been constructed to examine the collagenolytic activity of MMP family members. The present chapter provides an overview of MMP and related FRET substrates and describes how to construct and utilize these substrates.

Structural characterization of the ectodomain of a disintegrin and metalloproteinase-22 (ADAM22), a neural adhesion receptor instead of metalloproteinase: insights on ADAM function

ADAMs (a disintegrin and metalloproteinases) are a family of multidomain transmembrane glycoproteins with diverse roles in physiology and diseases, with several members being drug targets for cancer and inflammation therapies. The spatial organization of the ADAM extracellular segment and its influence on the function of ADAMs have been unclear. Although most members of the ADAM family are active zinc metalloproteinases, 8 of 21 ADAMs lack functional metalloproteinase domains and are implicated in protein-protein interactions instead of membrane protein ectodomain shedding. One of such non-proteinase ADAMs, ADAM22, acts as a receptor on the surface of the postsynaptic neuron to regulate synaptic signal transmission. The crystal structure of the full ectodomain of mature human ADAM22 shows that it is a compact four-leaf clover with the metalloproteinase-like domain held in the concave face of a rigid module formed by the disintegrin, cysteine-rich, and epidermal growth factor-like domains. The loss of metalloproteinase activity is ensured by the absence of critical catalytic residues, the filling of the substrate groove, and the steric hindrance by the cysteine-rich domain. The structure, combined with calorimetric experiments, suggests distinct roles of three putative calcium ions bound to ADAM22, with one in the metalloproteinase-like domain being regulatory and two in the disintegrin domain being structural. The metalloproteinase-like domain contacts the rest of ADAM22 with discontinuous, hydrophilic, and poorly complemented interactions, suggesting the possibility of modular movement of ADAM22 and other ADAMs. The ADAM22 structure provides a framework for understanding how different ADAMs exert their adhesive function and shedding activities.

The C-terminal domains of ADAMTS-4 and ADAMTS-5 promote association with N-TIMP-3

We investigated whether the affinity of tissue inhibitor of metalloproteinases (TIMP)-3 for adamalysins with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5 is affected by the non-catalytic ancillary domains of the enzymes. For this purpose, we first established a novel method of purifying recombinant FLAG-tagged TIMP-3 and its inhibitory N-terminal domain (N-TIMP-3) by treating transfected HEK293 cells with sodium chlorate to prevent heparan sulfate proteoglycan-mediated TIMP-3 internalization. TIMP-3 and N-TIMP-3 affinity for selected matrix metalloproteinases and forms of ADAMTS-4 and -5 lacking sequential C-terminal domains was determined. TIMP-3 and N-TIMP-3 displayed similar affinity for various matrix metalloproteinases as has been previously reported for E. coli-expressed N-TIMP-3. ADAMTS-4 and -5 were inhibited more strongly by N-TIMP-3 than by full-length TIMP-3. The C-terminal domains of the enzymes enhanced interaction with N-TIMP-3 and to a lesser extent with the full-length inhibitor. For example, N-TIMP-3 had 7.5-fold better K(i) value for full-length ADAMTS-5 than for the catalytic and disintegrin domain alone. We propose that the C-terminal domains of the enzymes affect the structure around the active site, favouring interaction with TIMP-3.

Analysis of flavonoid-based pharmacophores that inhibit aggrecanases (ADAMTS-4 and ADAMTS-5) and matrix metalloproteinases through the use of topologically constrained peptide substrates

Polyphenolic natural products from green tea and red wine have been identified as metalloproteinase inhibitors. Members from the flavonoid and stilbene families found to possess metalloproteinase inhibitory activities include (-)-epigallocatechin gallate, (-)-epicatechin gallate and piceatannol, but their minimally active pharmacophores have not been evaluated. The present study has examined compounds that are structural components of or structurally related to (-)-epigallocatechin gallate, (-)-epicatechin gallate and piceatannol for inhibition of aggrecanases and four representative matrix metalloproteinases. Piceatannol and pyrogallol were found to inhibit all aggrecanases and matrix metalloproteinases studied, indicating a crucial reliance on multiple hydroxyl groups for (-)-epigallocatechin gallate, (-)-epicatechin gallate and piceatannol activity. Differences in K(i) values for pyrogallol as determined with two structurally distinct substrates indicated the likelihood that this compound binds in a non-competitive modality. Further analysis showed that pyrogallol acts as an exosite inhibitor, consistent with the action of (-)-epigallocatechin gallate. In contrast, piceatannol was shown to be a competitive binding inhibitor and showed no differences in apparent K(i) values as determined by distinct substrates, illustrating the benefits of using two structurally distinct substrates to assist the analysis of protease inhibitors. The compounds identified here could be utilized to develop novel metalloproteinase probes or as fragment components of more active inhibitors.

Structural and inhibition analysis reveals the mechanism of selectivity of a series of aggrecanase inhibitors

Several inhibitors of a series of cis-1(S)2(R)-amino-2-indanol-based compounds were reported to be selective for the aggrecanases, ADAMTS-4 and -5 over other metalloproteases. To understand the nature of this selectivity for aggrecanases, the inhibitors, along with the broad spectrum metalloprotease inhibitor marimastat, were independently bound to the catalytic domain of ADAMTS-5, and the corresponding crystal structures were determined. By comparing the structures, it was determined that the specificity of the relative inhibitors for ADAMTS-5 was not driven by a specific interaction, such as zinc chelation, hydrogen bonding, or charge interactions, but rather by subtle and indirect factors, such as water bridging, ring rigidity, pocket size, and shape, as well as protein conformation flexibility.

Production, crystallization and preliminary crystallographic analysis of an exosite-containing fragment of human von Willebrand factor-cleaving proteinase ADAMTS13

ADAMTS13 is a reprolysin-type metalloproteinase belonging to the ADAMTS (a disintegrin and metalloproteinase with thrombospondin type 1 motif) family. It specifically cleaves plasma von Willebrand factor (VWF) and regulates platelet adhesion and aggregation. ADAMTS13 is a multi-domain enzyme. In addition to the N-terminal metalloproteinase domain, the ancillary domains, including a disintegrin-like domain, a thrombospondin-1 type 1 repeat, a Cys-rich domain and a spacer domain, are required for VWF recognition and cleavage. In the present study, a fragment of the ADAMTS13 ancillary domains (ADAMTS13-DTCS; residues 287-685) was expressed using CHO Lec cells, purified and crystallized. Diffraction data sets were collected using the SPring-8 beamline. Two ADAMTS13-DTCS crystals with distinct unit-cell parameters generated data sets to 2.6 and 2.8 A resolution, respectively.

Essential role of the disintegrin-like domain in ADAMTS13 function

ADAMTS13 is a highly specific multidomain plasma metalloprotease that regulates the multimeric size and function of von Willebrand factor (VWF) through cleavage at a single site in the VWF A2 domain. The precise role that the ADAMTS13 disintegrin-like domain plays in its function remains uncertain. Truncated ADAMTS13 variants suggested the importance of the disintegrin-like domain for both enzyme activity and specificity. Targeted mutagenesis of nonconserved regions (among ADAMTS family members) in the disintegrin-like domain identified 3 of 8 ADAMTS13 mutants (R349A, L350G, V352G) with reduced proteolytic activity. Kinetic analyses revealed a 5- to 20-fold reduction in catalytic efficiency of VWF115 (VWF residues 1554-1668) proteolysis by these mutants. These residues form a predicted exposed exosite on the surface of the disintegrin-like domain that lies approximately 26 A from the active site. Kinetic analysis of VWF115 carrying the D1614A mutation suggested that Arg349 in the ADAMTS13 disintegrin-like domain interacts directly with Asp1614 in VWF A2. We hypothesize that this interaction assists in positioning the scissile bond within the active site of ADAMTS13 and therefore plays a major role in determining cleavage parameters (K(m) and k(cat)), as opposed to binding affinity (K(d)) of ADAMTS13 for VWF, the latter being primarily determined by the spacer domain.

Conserved sequence in the aggrecan interglobular domain modulates cleavage by ADAMTS-4 and ADAMTS-5

BACKGROUND

Cleavage of aggrecan by ADAMTS proteinases at specific sites within highly conserved regions may be important to normal physiological enzyme functions, as well as pathological degradation.

METHODS

To examine ADAMTS selectivity, we assayed ADAMTS-4 and -5 cleavage of recombinant bovine aggrecan mutated at amino acids N-terminal or C-terminal to the interglobular domain cleavage site.

RESULTS

Mutations of conserved amino acids from P18 to P12 to increase hydrophilicity resulted in ADAMTS-4 cleavage inhibition. Mutation of Thr, but not Asn within the conserved N-glycosylation motif Asn-Ile-Thr from P6 to P4 enhanced cleavage. Mutation of conserved Thr residues from P22 to P17 to increase hydrophobicity enhanced ADAMTS-4 cleavage. A P4' Ser377Gln mutant inhibited cleavage by ADAMTS-4 and -5, while a neutral Ser377Ala mutant and species mimicking mutants Ser377Thr, Ser377Asn, and Arg375Leu were cleaved normally by ADAMTS-4. The Ser377Thr mutant, however, was resistant to cleavage by ADAMTS-5.

CONCLUSION

We have identified multiple conserved amino acids within regions N- and C-terminal to the site of scission that may influence enzyme-substrate recognition, and may interact with exosites on ADAMTS-4 and ADAMTS-5.

GENERAL SIGNIFICANCE

Inhibition of the binding of ADAMTS-4 and ADAMTS-5 exosites to aggrecan should be explored as a therapeutic intervention for osteoarthritis.