基质金属蛋白酶13-是一种Zn 2+依赖的基质金属蛋白酶,主要在结缔组织中表达

肝纤维化肝纤维化简介肝纤维化是指肝脏纤维结缔组织的过度沉积,是纤维增生和纤维分解不平衡的结果。

纤维增生是机体对于损伤的一种修复反应，各种病因所致反复或持续的慢性肝实质炎症,坏死可导致肝脏持续不断的纤维增生而形成肝纤维化，从许多慢性肝病，特别是慢性病毒性肝炎的临床及病理演变来看,肝纤维化和肝硬化是连续的发展过程，二者难以截然分开。

病因肝纤维化是由什么原因引起的？肝纤维化的发生机制肝脏贮脂细胞是产生各种细胞外基质的主要来源。

在肝脏纤维化的发生和发展过程中贮脂细胞激活转化为肌成纤维细胞样细胞（Myofibrblast-like cells）和成纤维细胞（Fibroblast），因而贮脂细胞的激活过程已成为肝纤维化发生机制研究的焦点之一。

调节贮脂细胞的因子可分为不溶性和可溶性两类，前者为各种细胞外基质，后者包括各种生长因子、细胞因子。

正常肝脏血窦内皮下的功能性基底膜（Ⅳ型胶原和层连蛋白）对于维持贮脂细胞的静止状态（贮存Vit.A，分泌Ⅳ型胶原）起重要作用，一旦基底膜遭到破坏，贮脂细胞的表型即可发生改变。

调节贮脂细胞的细胞因子和生长因子很多。

能够促进其增殖的有PDGF，EGF，IGF-1,FGF-2，TGF-α；能抑制其增殖的有视黄醇和维甲酸及内皮素；TGF-β本身对贮脂细胞的生长有抑制作用，但通过刺激PDGF和FGF-2的表达又可促进其生长。

在这些细胞因子中以TGF-β1和PDGF研究得较为深入。

在肝脏中TGF-β1主要由贮脂细胞、Kupffer细胞、内皮细胞、血小板及肝细胞产生，通过旁分泌对其他细胞发生调节作用。

TGF-β1可促进贮脂细胞表达和分泌Ⅰ、Ⅲ、Ⅳ型胶原、纤维连接蛋白、细胞粘合素、软骨连接蛋白、血栓粘合素、Biglycan及Decrin。

而且还可通过自分泌作用促进TGF-β1自身的表达，它对金属基质蛋白酶（胶原酶、基质分解素）和纤溶酶原激活物的表达有抑制作用，而且可促进内皮细胞和贮脂细胞表达纤溶酶原激活物抑制因子（PAI-1）和金属蛋白酶组织抑制因子（TIMP）。

生命科学研究LIFE SCIENCE RESEARCH1999年 第3卷 第3期 Vol.3 No.3 1999基质金属蛋白酶吴二喜　王凤飞　Norman McKIE摘　要：基质金属蛋白酶是一类分解细胞外基质组分的锌蛋白酶。

它们在有机体生长发育中的细胞外基质逆转与重塑以及疾病中的病理损害起着极为重要的作用。

基质金属蛋白酶的表达和活性在不同细胞水平受到严密调控，如细胞因子、生长因子以及激素的调节。

基质金属蛋白酶以酶原形式分泌，随后被其它蛋白酶如胞浆素或非蛋白酶类化学物质如有机汞所激活。

所有基质金属蛋白酶都受到天然抑制剂金属蛋白酶组织抑制剂所抑制。

两者的不平衡导致许多疾病的发生，如肿瘤侵入及转移。

合成基质金属蛋白酶组织抑制剂所抑制，如Marimastat能控制肿瘤转移的发生及进一步扩散。

本文将对基质金属蛋白酶的特征、分子区域结构、底物特性、激活机制、调控方式等方面进行最新概述。

关键词：基质金属蛋白酶；金属蛋白酶组织抑制剂；胶原酶；明胶酶；基质酶；膜型基质金属蛋白酶中图分类号：Q51；Q55 文献标识码：AMatrix MetalloproteinasesWU Er-xi1*，WANG Feng-fei1*，Norman McKIE2（1．Department of Human Metabolism and Clinical Biochemistry，University of Sheffield Medical School，Beech Hill Road，Sheffield S10 2RX，UK； 2．Department of Rheumatology，University of Newcastle-upon-Tyne Medical School Framlington Place，Newcastle-upon-Tyne NE2 4HH，UK）Abstract：Matrix metalloproteinases (MMPs) are zinc proteinases that degrade compounds of the extracellular matrix (ECM). These enzymes play a pivotal role in turnover and remodelling of the ECM during organism growth and development and the pathological destruction of tissues in diseases. The activities of metalloproteinases are tightly controlled at several different cellular levels such as modulation by cytokines, growth factors and hormones. MMPs are secreted as zymogens which can be activated by other proteinases such as plasmin or non-proteolytic agents such as organomercurials. All MMPs are inhibited by their natural inhibitors,tissue inhibitors of matrix metalloproteinases(TIMPs). Imbalance between MMPs and TIMPs has been implicated in many diseases such as tumour invasion and metastasis. The synthetic MMP inhibitors such as Marimastat can prevent the growthand further spread of established metastases.Key words：MMPs；TIMPs；collagenases；gelatinases；stromelysins；membrane type MMPsT0　Introduction Matrix metalloproteinases (MMPs) are also called matrixins. Since the first MMP was discovered by Gross and Lapiere in 1962, numerous other MMPs have been described and characterized. To date at least 14 MMPs have been found (Table 1). According to their structural properties and substrate specificities, MMPs can be divided into sub-Table　1　The　matrix　metalloproteinase　family*Enzymes MMP No．**EC No．Mr（kDa）latent/activeExtracellular matrixsubstratesCollagenases Interstitial collagenase MMP1EC 3．4．24．757/48Collagen Ⅰ，Ⅱ，Ⅲ，Ⅶ，Ⅹ；gelatin，entactin，tenascin，aggrecan，progelatinaseA，progelatinase BNeutrophil collagenase MMP8EC3．4．24．3485/65Collagen Ⅰ，Ⅱ，Ⅲ；aggrecanCollagenase 3MMP13　60/48Collagen Ⅰ，ⅡGelatinases Gelatinase A MMP2EC 3．4．24．2472/66Collagen Ⅰ，Ⅳ，Ⅴ，Ⅶ，Ⅹ；gelatin，fibronectin，laminin，aggrecan elastin，progelatinase BGelatinase B MMP9EC 3．4．24．3592/84Collagen Ⅳ，Ⅴ；gelatin，elastin，entactin，aggrecan，vitronectinStromelysins Stromelysin 1MMP3EC 3．4．24．1760/50Collagen Ⅱ，Ⅳ，Ⅸ，Ⅹ，Ⅺ；gelatin，laminin，fibronectin，elastin，tenascin，aggrecan，procollagenase，progelatinase B，neutrophil procollagenaseStromelysin 2MMP10EC 3．4．24．2253/47Collagen Ⅳ，laminin，fibronectin，elastin，aggrecan，procollagenaseStromelysin 3MMP11　65/45Serpins，α1-PI，α2-antiplasmin，insulin-like growth factor-bindingprotein-1Others Matrilysin MMP7EC 3．4．24．2328/21Collagen Ⅳ，gelatins，laminin，fibronectin，entactin，elastin，aggrecan，progelatinaseA，progelatinase B，procollagenaseMetalloelastase MMP12EC．3．4．24．6552/43ElastinMembrane type MMPs MT1-MMP MMP14　63/54Progelatinase A，procollagenase 3，collagen，proteoglycan，fibronectin，tenascinMT2-MMP MMP15　72/61Progelatinase A，procollagenase 3，collagen，proteoglycan，fibronectin，tenascinMT3-MMP MMP16　64/55Progelatinase A MT4-MMP MMP17　70/54Unknown*Compiled from sources including Sang and Douglas[2]；Shingleton et al．[3]；Nagase [4]；Pei et al．[19]；Mari et al．[44]；Murphy et al．[96]；Takino et al．[28，46]andCockett et al．[116]**Some MMPs have been omitted．MMP5 and MMP2 are the same enzyme[5]，MMP4 and MMP6 have been described in only one laboratory and there are no sequence data to date [5]．There are some novel MMPs which have been found recently，see text for details．groups: collagenases, gelatinases, stromelysins, membrane type MMPs (MT-MMP) andothers[1～4]. This review summarises the characteristics, domain structure, substratespecificity, activation mechanisms, regulation, functions of the MMPs.1　Main characteristics of the MMPs All MMPs have a number of common characteristics which are also helpful to identify new members. These properties[2, 5～7]are: 1）they share a common domain structure comprising signal, propeptide, catalytic, and C- terminal hemopexin-like domains (except MMP7) (Fig．1).Fig．1　The domain structure of the matrix metalloproteinases2）They are secreted as zymogens. 3）Their activation can be achieved by other proteinases or organomercurials. 4）Their proteinase activity is blocked by 1,10-phenanthroline and chelating agents. 5）Activation is accompanied by a loss of molecular weight. 6）The active site contains metal ion zinc. 7）Their activity is inhibited by tissue inhibitor of metalloproteinases (TIMPs). 8）The active enzymes cleave one or more components of the extracellular matrix. 9）The enzymes act in neutral pH and need calcium ions for stability.2　Domain structure of MMPs After comparing the primary amino acid sequences of the MMP members, it can be seen that these proteins are divided into several distinct domains that are conserved among family members[1]. The largest MMP member (MMP9) has 7 domains in order from N-terminal: signal, propeptide, catalytic, fibronectin-like,α2V collagen-like, hinge, and C-terminal hemopexin-like. The simplest member MMP7 has only signal, propeptide and catalytic domains. The newly discovered MT-MMPs have a transmembrane domain[8]. All MMPs produce a signal as a leader sequence which cells cleave prior to secretion. The propeptide is lost on activation. For example, the human fibroblast collagenase is synthesized as a preproenzyme of Mr 54 kDa (57 kDa in Table 1) with the signal peptide of19 amino acids[9]. The primary secretion products of human fibroblast collagenase consist ofa minor glycosylated form of Mr 57 kDa and a major unglycosylated polypeptide of Mr 52 kDa[9]. 81 amino acids are removed after proteolytic activation of human fibroblast collagenase[9]. The catalytic domain contains a conserved zinc binding site comprising the sequence HEXGHXXGXXH[2]. The zinc acts as an active site and is ligated by the three-histidine residues of the zinc binding consensus sequence. The glutamic acid residue in the conserved zinc binding site acts as the catalytic base and proton shuttle during proteolysis and is involved in the fixation of a zinc-bound water molecule[10]. The structural integrity of the zinc-binding active site is maintained by a conserved methionine that is called “Met-turn”[10]. The catalytic domain also contains a calcium-binding region where the calcium ion is believed to stabilize the enzyme[11]. With the exception of matrilysin (MMP7), the MMPs contain an additional feature, that is their hemopexin-like or vitronectin-like C-terminal domain[1]. This domain is thought to help determine substrate specificity[1,5]. Thiscould be true, since recently Gohlke et al.[12]have found that the topology and the side chain arrangements of gelatinase A (MMP2) and fibroblast collagenases are very similar, but there are significant differences in surface charge and contouring. They thought these differences may be a factor in allowing the MMP2 C-terminal domain to bind to TIMP2. Very recently, Brooks et al.[13,14]have found that MMP2 can bind αvβ3 through its hemopexin-like domain. Besides the prototype domain structure, the gelatinases contain three tandem domains with sequences similar to the collagen-binding domain of fibronectin. The fibronectin-like domain is thought to be involved in the binding of two gelatinases to their substrate[5]. The MT-MMPs contain a transmembrane domain and a furin recognition site which is also found in stromelysin 3[8,15](Fig．1).3　Substrate specificity of MMPs The collagenases mainly cleave interstitial collagens (type I, II and III), unlike other MMPs, their substrate specificity is well defined. Collagenase action on the α2-macroglobulin results in the cleavage of Gly-Leu Peptide bond[5]．They cleave the Gly-Ile peptide bond of α1(I) chain of collagen and Gly-Leu peptide bond of α2(I) chain of collagen[5]. The substrate cleavage pattern for collagenases is that P1 "residue is invariably hydrophobic (Leu, Ile, Val) and that P1 is usually Gly or a hydrophobic residue[5,16]. The gelatinases cleave denatured collagens and type IV collagen. As shown in table 1, while gelatinase A (MMP2) can also cleave the fibronectin and laminin, major components of the basement membrane, gelatinase B (MMP9) can only cleave the basement membrane component entactin[2]. Stromelysin 1 and 2 have a broad pH optimum and more general activity and are able to degrade many ECM proteins including proteoglycans, gelatins, fibronectin, laminin, elastin, type IV collagen and type IX collagen[17]． Niedzwiecki et al.[18]tested the substrate specificity of the human stromelysin 1 and found the preferences at P3, P2, P1, P1 ", and P2 "are for the hydrophobic amino acids Pro, Leu, Ala, Nva, and Trp, respectively. The mature stromelysin 3 does not degrade any major ECM components. Up to now, the only known substrates for stromelysin 3 are α1-proteinase inhibitor, serine proteinase inhibitors, α2-antiplasmin, and insulin-like growth factor-binding protein-1 [19,20]. However, the substrate specificity overlaps among the MMP members. The gelatinase A (MMP2) can also cleave triple helical type I collagen generating the 3/4 and 1/4 length collagen fragments characteristic of interstitial collagenases[21]. The cleavage site is the same Gly-Ile/Leu bond as the interstitial collagenases[21]. In fact all of the MMPs cleave gelatin and fibronectin at some rate[1]. Almost every MMP degrades an octapeptide containing collagen sequence GPQGIAGQ[5].4　Activation mechanisms of MMPs The MMPs are secreted in a latent form that is subsequently converted into the mature enzymes. The inactive zymogen can be processed into active forms by numerous reagentsincluding proteinases such as trypsin and plasmin; conformational perturbants such as sodium dodecyl sulfate (SDS); heavy metals such as Au (I) compounds and organomercurials; oxidants such as NaSCN; disulfide reagents such as oxidized glutathione; and sulfhydryl alkylating agents such as N-ethylmaleimide[22]. The latent proform of MMPs contains the highly conserved PRCGVNPD sequence with an unpaired cysteine residue. The cysteine residue links to the active site zinc, which blocks the active site. A ‘cysteine switch’　activation mechanism has been proposed[22,23](Fig． 2). In other words, in the latent form of MMPs, the cysteine residue with the thiol group coordinates the catalytically essential zinc ion in the active site of enzyme. Some reagents such as SDS can dissociate the cysteine residue from the zinc ion[22]. From this hypothesis, each MMP should have an unpaired cysteine residue and a zinc-binding site. In fact, all MMPs contain the PRCGVNPD sequence with an unpaired cysteine residue in the propeptide domain and the HEXXHXXGXXH sequence in the catalytic domain. Very recently, it has been shown that he structure of human pro-MMP2 supports this hypothesis[24]. The loops within the propeptide domain act as bait for activating proteinases. The prodomain structure breaks down and its shielding of the catalytic cleft is withdrawn upon cleavage, which allow water to enter and hydrolyze the coordination of the cysteine residue to the zinc ion[24]. All MT-MMPs found to date and stromelysin 3 contain a consensus sequence RXR/KR, which has already been found to be essential in the activation of stromelysin 3 and MT1-MMP by furin [15,25,26]. MMPs also have the ability to activate one another[27]. MT1-MMP[8]and MT3-MMP[28]have been shown to activate MMP2. MMP7 can activate MMP1, MMP2, MMP3 and MMP9[29]. MMP3 activates MMP1[30], MMP8[31], MMP9[32]and MMP13[33]. MMP2 and MT1-MMP activate MMP13[34], while MMP10 activates MMP8[35]. It has also been well documented that MMPs and serine proteinases can act on the proforms of one another [36,37]. Plasmin can cleave the prodomains of MMPs such as collagenase and stromelysin and activate these enzymes[36,37]. MMP7 can catalyze the formation of low molecular weight pro-urokinase and urokinase[38].Fig．2　Cysteine switch mechanism for activation of MMPsProteinases such as trypsin and plasmin cleave the propeptide，ahead of the cysteine to generate intermediate forms．Alternatively，nonproteolytic agents such as aminiphenyl-mercuric acetate （APMA） and sodium dodecy1 sulfate （SDS） will modify the cysteine．In a second step，these intermediate forms can be autoproteolytically cleaved to remove the propeptide and confer permanent activity．5　Regulation of MMPs The activities of metalloproteinases are tightly controlled at several different cellular levels. There are five points: (i) modulation of gene expression by cytokines, growth factors and hormones; (ii) synthesis and secretion of proMMPs; (iii) selective expression of MMP genes in specific tissue/cell types; (iv) activation of proenzymes; and (v) inhibition of the active enzymes[7,36,39,40]. It is known that the MMPs are not constitutively expressed in most tissue types but their mRNAs can be induced by treatment with many kinds of agents such as cytokines, growth factors, hormones, tumour promoter and oncogene products. In some cases the induction of more than one MMP is coordinately regulated, for example, MMP1 and MMP3 are often coordinately expressed[40]. The synthesis of MMP1 and MMP3 can be upregulated by 12-O-tetradecanoyl-phorbol-13-acetate (TPA), interleukin 1 (IL1), tumor necrosis factor α(TNFα), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF) and platelet derived growth factor (PDGF) and be downregulated by transforming growth factor β　(TGF-β), interferon γ (IFN-γ) retinoic acid and dexamethasone[40], and MMP1 is down regulated by IL4[41]. The selective expression of MMP genes in specific tissue/cell types is one method of regulation of MMPs. Interstitial collagenase (MMP1) arises from connective tissue fibroblasts and macrophages. Neutrophil collagenase (MMP8) is only produced by cells of the neutrophil lineage. Stromelysin 1 (MMP3) is not widely expressed normally, but can be readily induced by growth factors, cytokines, tumour promoters and oncogene products in cultured mesenchymal cells such as chondrocytes and connective tissue fibroblasts. Stromelysin 2 (MMP10) is usually expressed in macrophages, keratinocytes and tumour cells[40,42]. Stromelysin 3 (MMP11) is often expressed in tumour stromal cells[37,40,43,44]. Gelatinase A (MMP2) is the most widespead of all MMPs and is frequently elevated in malignancies as well as occurring in connective tissue cells[36,40]. Gelatinase B (MMP9) is expressed in transformed and tumour-derived cells, neutrophil, corneal epithelial cells, cytotrophoblasts and keratinocytes[36]. Matrilysin is expressed in immature monocytes[36]. Metalloelastase (MMP12) is found in macrophages. MT1-MMP is expressed in tumour stroma cells[45]. MT2-MMP is produced by a human oral malignant melanoma and a human placenta[46]. MT3-MMP is expressed in normal tissues such as lung and kidney and cultured cells such as the squamous cell carcinoma cell line OSC-19 and human embryonal lung fibroblasts[28]. MT4-MMP is expressed in primary breast carcinomas and breast cancer cell lines examined[47]. All MMPs are inhibited by natural inhibitors called tissue inhibitors of metalloproteinases (TIMPs) of which four have been described (Table 2). TIMPs 1, 2 and 4 are secreted extracellularly in soluble form whereas TIMP3 binds to the ECM. All TIMPs share 35%～40% sequence identity and considerable higher structural similarity. The TIMPs bind with high affinity and 1∶1 molar ratio to active MMPs resulting in the loss of proteinase activity. All TIMPs contain 12 cysteine residues that have been shown to form disulfide bonds generating 6 loops. The mechanism of inhibition of MMPs by TIMPs is widely felt to be unclear. Murphy[39]. pointed out that the TIMP C-terminal domain has several different MMP binding sites that act to increase the rate of inhibition. Further studies such as site-directed mutagenesis and the crystal structure research of the complex of MMP and TIMP will facilitate understanding of the mechanism. TIMPs play a pivotal role in the regulation of ECM degradation/remodelling. Disruption of the balance between MMPs and TIMPs has been implicated in many diseases such as tumour invasion and metastasis. Besides their inhibitory activities, the TIMPs play a role in growth-promotion[48]. Some effective synthetic MMP inhibitors also can inhibit MMPs[49,50]. For example, the hydroxamate-based inhibitors such as BB94 (batimastat) and BB2516 (marimastat) can inhibit metastatic spread of tumoursand block the process of tumour neovasculariation[51～54]. The hydroxamate group in thesemolecules can combine with the zinc atom in the active site of MMPs[49,50].Table 2　Comparison of TIMP family members*　TIMP1TIMP2TIMP3TIMP4 Molecular mass28kDa21kDa24kDa22kDa Glycosylation yes no no/yes no Binding properties proMMP9proMMP2ECM proMMP2Transcripts0.9kb 1.1 and 3.5kb 4.5,2.8,2.4and 1.2kb1.4，4.1，2.1，1.2，and 0.97kbModulation of gene expression by TGF-β1updown or noobvious effectup not determinedMajor sites ofexpressionOvary，bone Placenta Kidney，brain Heart Chromosome locationof human genexq1117q2522q12.1～13.22p25 *Compiled from sources including Stetler-Stevenson[117]；Greene et al．[118]；Wick et al．[119]；Chamber and Matrisian[120]and Olson et al．[121]6　MMPs in physiological processes and pathological destruction Normal expression of MMPs is associated with turnover and remodelling of the ECM during growth and development. Cawston[7]summarised the involvement of MMPs in the normal turnover of connective tissue matrix. The MMPs are involved in the normal physiological processes such as ovulation and embryo implantation, embryological development, angiogenesis, bone turnover, uterine resorption and cervical ripening[7]. The MMPs are associated with the pathological destruction of tissues in diseases[1,7]. They are implicated in the processes such as wound healing, corneal ulceration, tumour growth and metastasis, periodontal disease, rheumatoid arthritis, arteriosclerosis and aortic aneurism[1,7]. Considerable research has been directed toward understanding both the steps involved in tumour cell invasion and metastasis and the molecular mechanism of the process. MMPs are thought to be one of the main contributors to tumour invasion and metastasis since they can degrade all of the components of basement membranes which the tumour cellsmust traverse[55～58]. Now the gene-targeting experiments have facilitated the examinationsof the effects that their absence, mutation or overexpression, in various physiological and pathological processes[59]. In the following sections more detailed information is presented on several MMP family members.7　Collagenases I, II and III (MMP1, MMP8 and MMP13) The group of enzymes termed collagenases includes 3 members: MMP1 (interstitialcollagenase or fibroblast collagenase), MMP8 (neutrophil collagenase) and MMP13 (collagenase 3). Their sequences share around 50%[33]. They cleave all three α chains of native types I, II, III collagens at a single site resulting in fragments corresponding to three-quarters and one-quarter of their initial length by hydrolyzing the peptide bond Gly-[Ile orLeu][60～62]. They do not degrade collagen IV and V, which are cleaved by otherproteinases[63～66]. The collagenases can also cleave type X collagen[67]. The threecollagenases have their own preference in cleaving the collagens. The preferred substrate of collagenase 3 (MMP13) is collagen type II[33], fibroblast collagenase (MMP1) preferentially cleaves collagen type III[68]and neutrophil collagenase (MMP8) prefers to cleave type I collagen[69]. Also collagenase 3 has a much stronger gelatinolytic activity than its homologous counterparts MMP1 and MMP8[33]. To date MMP1 expression has not been found in rats or mice[33]. All collagenases are located in the human chromosome 11q22.3 cluster[70,71]and share a highly conserved gene structure[72,73]. The expression of MMP13 in cartilage and its preference to degrade type II collagen suggests that it plays a critical role in the arthritides[74]. X ray crystallographic analyses of MMP1 and MMP8 are available now. The structures show that their catalytic domains harbour two zinc ions and one or twocalcium ions[75～77]. The structure consists of a five-stranded β sheet and three α helices[75].8　Gelatinases A and B (MMP2 and MMP9) Gelatinases, also called type IV collagenases, contain two members: MMP2 and MMP9. They degrade denatured collagens, type IV, V, VII, X, and XII collagens,vitronectin, aggrecan, elastin, galectin 3 and laminin[78～83]. Recently, it has beendemonstrated that MMP2 degrades native interstitial collagens[21]. MMP2 is the most widely distributed MMP[1]. Overexpression of gelatinases has been demonstrated in many tumorsystems and has been linked to tumour invasion[84～87]. While the proMMP2 is often foundcomplexed with the TIMP2 and is activated by MT1-MMP[88,89], the proMMP9 is associated with the TIMP1[78,90]. The regulation of MMP2 and MMP9 gene expression is different[91]. The promoter of MMP9 gene has a TATA-like sequence and a TPA response element, while MMP2 gene has no TATA motif-like sequence in the vicinity of the start site for transcription and TPA response element in its promoter[91]. There is a structural difference between MMP2 and MMP9 that comprises an extended 54 amino acid hinge region sequence which shares some homology with the α2 chain of type V collagen[78]. Brooks et al.[13,14]have found that MMP2 can directly bind integrin αvβ3. They further demonstrated that MMP2 binds αvβ3 through its hemopexin-like domain. It is likely to be distinct from other αvβ3-directed ligands as MMP2 has no RGD sequence[13,14]. Brooks et al.[14]have also found that PEX, a fragment of MMP2, which contains the C-terminal hemopexin-like domain, prevents MMP2 binding to αvβ3 and blocks cells surfacecollagenolytic activity. PEX is likely to be a natural breakdown product of MMP2 since the active form (62 kDa) of MMP2 can be further processed to a smaller species (43 kDa) resulting from autocatalytic removal of the 29　kDa hemopexin-like domain without the presence of TIMP2[14,92]. Both MMP2 and MMP9 are located on human chromosome 16[93].9　Stromelysins 1, 2 and 3 (MMP3, MMP10 and MMP11) MMP3 (stromelysin 1), MMP10 (stromelysin 2) and MMP11 (stromelysin 3) belong to this group. Stromelysins have wide substrate specificity. Stromelysin 1 degrades aggrecan, fibronectin， gelatin， laminin， type II， IV， IX， X， XI collagens and elastin[2,94]. It also participates in activation of other proMMPs such as proMMP1, proMMP8 and proMMP9[31,32,80]. MMP3 is not readily expressed in tissue but can be induced by cytokines such as IL1 and TNFα, growth factors and tumour promoters such as PMA[1,5,95]. Stromelysin 2 cleaves aggrecan, laminin, fibronectin, elastin and type IV[2]. It is transcriptionally active in normal human cells such as keratinocytes and it encodes the secreted Stromelysin 2[42]. Stromelysin 3 is a newly characterized MMP. It can degrade serpin, α1-proteinase inhibitor (α1-PI), α2-antiplasmin, and insulin-like growth factor-binding protein-1[19,20]; the truncated stromelysin 3 can also degrade fibronectin, laminin, aggrecan and type IV[96]. Stromelysin 3 is often found expressed in stromal cells surrounding primary and metastatic carcinomas[43]and may be involved in promoting local tumor development. Recently it has been suggested that the tumor-specific processing of stromelysin 3 to the 35 kDa protein is likely to be an important regulatory mechanism, since the generation of 35 kDa stromelysin in tumour/stroma coculture requires basic fibroblast growth factor (bFGF) and an MMP-like enzyme[44]. Unlike other MMPs, prodomain of stromelysin 3 contains a furin cleavage site, and therefore stromelysin 3 can be processed directly to its 45 kDa active form by furin within the constitutive secretory pathway[15]. MMP3 and MMP10 are located in the human chromosome cluster 11q22.3[70,72], while MMP11 is mapped to the Q11.2 region of chromosome 22[97]．10　Membrane type-matrix metalloproteinases (MMP15, MMP16, MMP17 and MMP18) Membrane type matrix metalloproteinases (MT-MMPs), comprising MT1-MMP, MT2-MMP2, MT3-MMP and MT4-MMP (MMP14, MMP15, MMP16 and MMP17, respectively) are a novel subgroup of MMPs which contain a transmembrane domain and a short cytoplasmic domain in addition to the signal, pro-, catalytic, hemopexin-like and C-terminal domains which are common to other MMPs. To date, four MT-MMPs have been described [8,28,47,98]. From the alignment of amino acid sequences for MT-MMPs[47], it can be seen that they have at least 30% sequence homology to each other. Like other MMPs, they contain cysteine switch sequence, zinc binding site and Met-turn. However, they have an insertion between the propeptide and the catalytic domain in addition to the above mentionedmembrane-binding domain and short cytoplasmic domain. This insertion as in stromelysin 3 contains a potential cleavage site of furin or furin like convertase[8,15]. It has already been demonstrated that furin can cleave this sequence in pro-stromelysin 3 and proMT1-MMP [15,25,26]. However, the proMT1-MMP is proteolytically activated by human plasmin[99]. Okumura et al.[99]proposed that this is an extracellular proteinase activator of proMT1-MMP whereas the intracellular mechanism of activation is mediated by furin or a furin-like enzyme. The second insertion is found in proteinase domain; the function of these 8 amino acids is not known. The third insertion which contains the hydrophobic transmembrane domain is located in the C-terminal. The transmembrane domain of MT-MMPs plays an essential role in the progelatinase A (proMMP2) activation function of MT-MMPs, although some portions of the truncated form remain on the cell surface after the removal of this domain[100]. In MT1-MMP, the activation complex is a trimer comprising MT1-MMP, progelatinase A and TIMP2[88,89]. A recent study has suggested that MT1-MMP is a TIMP2 receptor[101]. This is further confirmed by another recent study[73]that TIMP2 and MT1-MMP form a complex for activation of progelatinase A. TIMP2 and TIMP3 can efficiently inhibit MT1-MMP whereas TIMP1 is a poor inhibitor for MT1-MMP[102]. Will et al.[102] also demonstrated that TIMP2 and TIMP3 can bind more rapidly to the catalytic domain of MT1-MMP than to the catalytic domain of MMP2. At the same time, two groups showed that MMP14, MMP15 and MMP16 locate in chromosomes 14, 16 and 8, respectively [103,104]. The MT-MMP gene loci are dispersed whereas most MMPs are clustered on chromosome 11q22.3[70,71], suggesting that the MT-MMPs may be a genetically distinct subgroup of MMPs. It has been suggested that the MT-MMPs play a critical role in tumor cell invasion and in ECM degradation[8,57,102]. MT-MMPs also can degrade ECM components[25,105,106].11　Others This group includes MMPs such as matrilysin (MMP7) and metalloelastase (MMP12). Matrilysin, also called putative metalloproteinase 1 (pump 1), is the smallest member of the MMP family. Unlike other MMPs, it lacks a C-terminal hemopexin-like domain. MMP7 can degrade various ECM components. It also can activate other proMMPs such as proMMP1, 3, 2 and 9[29]. Metalloelastase (MMP12) is also called macrophage elastase (ME). The expression of human macrophage elastase (HME) is mainly restricted to tissue macrophages [107]. Besides the substrate elastin listed in Table 1, the purified recombinant HME can degrade fibronectin, laminin, entactin, type IV collagen, chondroinan sulfate, and heparan sulfate[108]. Chandler et al.[109]also demonstrated that HME can degrade myelin basic protein and processes a TNF α fusion protein. Therefore Gronski et al.[108]suggested that HME may be essential for macrophages to penetrate basement membranes and remodel injured tissue during inflammation. MMP7 and MMP12 are allocated in the human chromosome cluster 11q22.3[70,72,107].。

基质金属蛋白酶识别位点全文共四篇示例，供读者参考第一篇示例：基质金属蛋白酶是一类重要的蛋白水解酶，具有广泛的生物学功能，参与细胞信号传导、细胞凋亡、生长因子的处理等多个生物过程。

基质金属蛋白酶通过特定的识别位点来识别和切割底物蛋白，其活性和底物的结合受到这些识别位点的影响。

本文将探讨基质金属蛋白酶的识别位点的特点及其在蛋白水解中的作用。

基质金属蛋白酶主要分为三个家族，包括MMP家族（基质金属蛋白酶）、ADAM家族（金属蛋白酶，TACE）以及ADAMTS家族（胶原蛋白酶）。

这些家族在底物识别和水解的方式上略有不同，但都需要通过识别位点来与底物蛋白结合并进行水解。

识别位点是一段特定的氨基酸序列，在底物蛋白中具有较强的保守性，基质金属蛋白酶通过与识别位点的结合来确定底物的切割位置。

基质金属蛋白酶的识别位点通常包括一个受氨基酸序列和一个特定的酶切位点。

受氨基酸序列是指位于识别位点周围的氨基酸序列，这些氨基酸在与基质金属蛋白酶结合时起到辅助作用。

酶切位点是指在受氨基酸序列和底物蛋白之间的具有特殊功能的氨基酸，基质金属蛋白酶在识别位点与酶切位点结合后进行切割。

不同的基质金属蛋白酶具有不同的受氨基酸序列和酶切位点，这也决定了它们的底物特异性。

基质金属蛋白酶在识别位点与底物蛋白结合后，通过底物蛋白的构象变化来促进水解反应的进行。

一般来说，底物蛋白在与基质金属蛋白酶结合时会发生构象变化，使得酶切位点更容易被基质金属蛋白酶识别和切割。

这种构象变化是基质金属蛋白酶与底物蛋白结合的关键步骤，也是水解反应进行的前提。

第二篇示例：基质金属蛋白酶（Matrix Metalloproteinase，MMPs）是一类在许多生物学和病理学过程中起关键作用的蛋白酶。

它们参与细胞外基质的降解和重塑，促进组织的发育和修复，同时也在许多疾病的发生和发展中扮演重要角色。

识别基质金属蛋白酶的底物位点对于研究其功能和生物学效应至关重要。

本文将就基质金属蛋白酶的识别位点展开讨论，以帮助读者更好地理解这些重要的酶类的作用机制。

基质金属蛋白酶在骨关节炎症性疾病中的研究进展发布时间：2022-04-28T04:50:17.945Z 来源：《世界复合医学》2022年2期作者：戴炯华，刘芳通信作者[导读] 基质金属蛋白酶（Matrix metalloproteinases，MMPs）是一类锌依赖性蛋白酶家族，其可通过降解细胞外基质、调控相应信号通路来参与细胞增殖、迁移、和分化等多种生物学过程[1]。

戴炯华，刘芳通信作者南华大学衡阳医学院岳阳市人民医院研究生协作培养基地，湖南衡阳421001【摘要】基质金属蛋白酶（Matrix metalloproteinases，MMPs）是一类锌依赖性蛋白酶家族，其可通过降解细胞外基质、调控相应信号通路来参与细胞增殖、迁移、和分化等多种生物学过程[1]。

MMPs在正常关节组织中低水平表达，而在关节炎症病理状态下表达明显增高，其参与调节炎症反应的各个方面，在骨关节炎、痛风性关节炎、类风湿性关节炎等发挥重要作用，本文对基质金属蛋白酶与骨关节常见炎症性疾病相关性研究进展做一综述，为科研提供便利。

【关键词】基质金属蛋白酶；骨关节炎；痛风性关节炎；类风湿性关节炎Research progress of matrix metalloproteinases in inflammatory diseases of bone and joint[Abstract]Matrix metalloproteinases(MMPs)are a family of zinc-dependent proteases,which can participate in various biological processes such as cell proliferation,migration and differentiation by degrading extracellular Matrix and regulating corresponding signal pathways[1].MMPs low level expression in normal joint tissues,and expressed in joint inflammation pathological condition significantly increased,to participate in the aspects of regulating the inflammatory response,in osteoarthritis,rheumatoid arthritis,gouty arthritis,etc play an important role,in this paper,matrix metalloproteinases and common inflammatory joint disease correlation research progress.[Key words]matrix metalloproteinase;osteoarthritis;gout arthritis;rheumatoid arthritis1.基质金属蛋白酶的概述人体正常的生长发育过程离不开细胞外基质(Extracellular matrix，ECM)适时的降解，ECM是一种大分子网络，其中胶原是ECM中最丰富的蛋白质，MMPs是唯一能够降解胶原的酶。

蛋白多糖-又称黏多糖，为基质的主要成分，是多糖分子与蛋白质结合而成的复合物蛋白多糖-又称黏多糖，为基质的主要成分，是多糖分子与蛋白质结合而成的复合物。

多糖部分为糖胺多糖，又称氨基已糖多糖，由成纤维细胞产生，主要分硫酸化和非硫酸化两类。

前一类主要有硫酸软骨素、硫酸角质素、硫酸肝素等；后一类为透明质酸，是曲折盘绕的长链大分子，构成蛋白质多糖复合物的主干，其他糖胺多糖则与蛋白质结合，形成蛋白多糖亚单位，后者再通过结合蛋白链与透明质酸长链分子形成蛋白多糖聚合体。

学术术语来源——温阳益髓中药干预兔膝骨关节炎软骨基质金属蛋白酶的表达文章亮点：1 实验的特点为发现温阳益髓中药对骨关节炎软骨中基质金属蛋白酶13表达的抑制作用极其显著，可以降低基质金属蛋白酶1的表达，其作用效果较盐酸氨基葡萄糖要略弱，对基质金属蛋白酶3表达具有显著的抑制作用，其作用强度比盐酸氨基葡萄糖更强。

2 作者认为，温阳益髓中药可以有效抑制软骨基质中基质金属蛋白酶的表达，通过抑制基质金属蛋白酶的表达减少软骨基质的降解，从而对关节软骨起到保护作用。

关键词：组织构建；软骨组织工程；温阳益髓；中药；骨关节炎；基质金属蛋白酶；软骨；盐酸氨基葡萄糖；北京市自然科学基金主题词：骨关节炎；软骨；中草药；基质金属蛋白酶摘要背景：目前临床上关于温阳益髓中药治疗膝骨关节炎对软骨基质金属蛋白酶表达影响的研究还较少有报道。

目的：制作兔膝骨关节炎模型观察温阳益髓中药对软骨基质金属蛋白酶表达的影响。

方法：健康成年新西兰大白兔96只，随机选取72只采用石膏外固定方法制作兔膝骨关节炎模型。

确定造模成功后再随机分为3组，模型组不做处理；中药治疗组每日灌胃方药提取液24 mL/kg，药物对照组每日灌胃葡立胶囊(盐酸氨基葡萄糖)24 mg/kg，1次/d，至造模成功后8周。

另外24只新西兰大白兔作为空白对照。

结果与结论：PCR方法定量分析骨关节炎模型组软骨组织中基质金属蛋白酶1、基质金属蛋白酶3、基质金属蛋白酶13表达水平均显著高于其他3组。

基质金属蛋白酶识别位点概述说明以及解释1. 引言1.1 概述:基质金属蛋白酶（matrix metalloproteinases, MMPs）是一类具有重要生物学功能的酶家族，广泛存在于人体和其他生物体内。

它们在细胞外基质的代谢、细胞迁移、炎症反应、组织修复等多种生物过程中扮演着关键角色。

基质金属蛋白酶通过降解与调控胶原蛋白、纤维连接蛋白等基质成分的结构，参与了许多疾病的发展和进展，如肿瘤转移、心脏病变以及风湿性关节炎等。

1.2 文章结构:本文将依次介绍基质金属蛋白酶的概述、识别位点的重要性以及该领域的研究方法和技术。

首先，我们将对基质金属蛋白酶进行分类定义，并探讨它们在结构和功能特点上的差异。

随后，我们将深入讨论基质金属蛋白酶在生理和病理过程中识别位点的意义，并介绍一些重要识别位点的例子和作用机制。

接下来，我们将详细介绍实验室技术手段、生物信息学分析方法以及基于计算模型预测识别位点的方法。

最后，我们将对基质金属蛋白酶识别位点研究现状进行总结归纳，并展望未来可能的研究方向和应用前景。

1.3 目的:本文旨在全面深入地探讨基质金属蛋白酶识别位点的概述、意义以及相关研究方法和技术。

通过对该领域的综述，我们希望能够提高人们对基质金属蛋白酶与其识别位点之间关系的理解，并促进该领域的进一步研究和应用。

同时，我们也期望为未来开展相关疾病治疗、药物设计等方面的工作提供参考和借鉴。

2. 基质金属蛋白酶概述：2.1 定义与分类：基质金属蛋白酶是一类广泛存在于细胞内和细胞外的酶，其特点在于能够催化多种蛋白质的降解和修饰过程。

它们主要通过断裂或修改细胞外基质中的蛋白质分子，从而参与了许多重要的生物学过程，如组织发育、炎症反应和肿瘤转移等。

基质金属蛋白酶按照结构、底物特异性以及金属离子需求等方面进行了分类，包括胶原酶、凝血酶样蛋白酶、凝血素样活化剂等多个亚族。

2.2 结构与功能特点：基质金属蛋白酶通常由一个完整的蛋白结构域组成，该结构域含有保守性高的催化位点和底物结合位点。

金属蛋白酶基质金属蛋白酶(matrix metalloproteinase,MMP)是一类结构中含Zn2+和Ca2+的蛋白水解酶类，主要参与细胞外基质的代谢。

它们在血管形成、伤口愈合、肿瘤浸润和纤维化等方面起着重要的作用，因此备受关注.1.1分类和功能目前已发现的基质金属蛋白酶已经超过14种，主要分为五类：间质胶原酶类，可降解间质胶原(Ⅰ、Ⅱ、Ⅲ型胶原)，包括MMP1、MMP8和MMP3；另一类为Ⅳ型胶原酶/明胶酶等，可降解基底膜Ⅳ型胶原和变性的间质胶原(明胶)，包括MMP2和MMP9；第三类为基质分解素类，可降解蛋白多糖、层粘连蛋白、纤维连接蛋白和Ⅳ型胶原，包括MMP3、MMP7和MMP10；第四类为膜型金属蛋白酶类(membrane-type MMP3,MT-MMPs)，是最近克隆克出来的MMP家庭新成员，并迅速成为研究热点，它包括MMP14、MMP15、MMP16和MMP17。

膜型金属蛋白酶类有双重功效：激活MMP2酶原(proMMP2)，降解细胞外基质；第五类包括MMP11和MMP12。

1.2 特性基质金属蛋白酶类有许多共同的特性；(1)其催化机制依赖于含锌离子的活化中心；(2)以酶原形式泌出；(3)酶原需经蛋白酶等水解和修饰后才有活性；(4)结构相似，cDNA序列上显示同源性；(5)能裂解一种或多种细胞外基质；(6)可被金属蛋白酶组织抑制剂(tissue inhibitor of metalloprotein-ase,TIMPs)或螯合剂EDTA所抑制。

1.3 金属蛋白酶组织抑制剂TIMPs同MMPs活性的主要抑制剂，目前已发现的有TIMP-1、TIMP-2、TIMP-3和TIMP-4四型。

关于TIMP的作用机理，可能是通过其17～19位上的亮氨酸—缬氨酸—异亮氨酸与MMP的S1′-S2′-S3′区结合，与MMP第16位上天冬氨酸残基的羧基和其活性中心的锌结合，从而抑制其活性。

TIMP不仅能与酶的催化位点结合，使酶失活，还能与酶原的某些位点结合，阻止酶原活化。

基质金属蛋白酶的调节及其疾病的治疗基质金属蛋白酶（MMPs）是一类参与异常细胞增生和组织修复的酶。

它们可以调节细胞外基质的降解和修复，参与维护组织的稳态和生长发育。

然而，MMPs过度活化或异常表达也可能导致多种疾病，如肿瘤、心脏病、风湿性关节炎等。

因此，对MMPs的调控和阻断正在成为治疗这些疾病的重要策略之一。

MMPs的结构和功能MMPs是一类具有高度保守结构域的Zn2+依赖性内切酶。

MMPs基本结构包括一个信号肽、一个质量约为120-130 kDa的前体蛋白、一个prodomain、一个catalytic domain、一个hemopexin-like domain和一个transmembrane domain。

这些结构域的组合和位置不同导致MMPs的活性和位置不同。

MMPs在细胞内和细胞外分别表达和调控。

它们能够降解和修复胶原蛋白、基质小分子和蛋白质等结构要素。

另外，MMPs还可以促进细胞迁移、增生和凋亡等与细胞信号传导有关的生物学进程。

MMPs的调控和疾病治疗MMPs的异常表达和活化在多种疾病中发挥作用。

例如，在肿瘤中，过度MMP-2活化可促进转移、侵袭和治疗难度；在心脏病中，MMP-9异常表达则能够促进心肌细胞凋亡和炎症反应。

因此，对MMPs的调控和阻断成为治疗这些疾病的重要策略之一。

目前，有多种方法可以调控和抑制MMPs的活性。

一些天然物质，如维生素D3和omega-3脂肪酸，已被证明可以调控MMPs的表达和活性。

此外，制备针对MMPs的抑制剂也成为治疗疾病的研究热点之一，这些抑制剂可以选择性抑制不同的MMPs亚型，并被广泛应用于肿瘤、心血管疾病的治疗中。

此外，其他一些方法也被应用于治疗相关疾病。

例如，在肿瘤治疗中，联合应用靶向药物和MMPs抑制剂能够提高治疗效果和减轻副作用。

在心脏病治疗中则使用心脏辅助装置来降低心脏负荷和减少MMPs的表达。

结论MMPs是一类重要的酶，在生物学进程中发挥重要作用。