MMP9 (matrix metallopeptidase 9 (gelatinase B, 92kDa gelatinase, 92kDa type IV collagenase))

	Domain structure of the MMP9. Pre: signal sequence; Pro: propeptide with a free zinc-ligating thiol (SH) group; Zn: zinc-binding site; II: collagen-binding fibronectin type II inserts; H: hinge region; The hemopexin/vitronectin-like domain contains four repeats with the first and last linked by a disulfide bond.
Description	MMP-9 is a Zn+2 dependent endopeptidase, synthesized and secreted in monomeric form as zymogen. The structure is almost similar to MMP2, another member of matrixmetalloproteinase family. The nascent form of the protein shows an N-terminal signal sequence ("pre" domain) that directs the protein to the endoplasmic reticulum. The pre domain is followed by a propeptide-"pro" domain that maintains enzyme-latency until cleaved or disrupted, and a catalytic domain that contains the conserved zinc-binding region. A hemopexin/vitronectin-like domain is also seen, that is connected to the catalytic domain by a hinge or linker region. The hemopexin domain is involved in TIMP (Tissue Inhibitors of Metallo-Proteinases) binding e.g. TIMP-1 & TIMP-3, the binding of certain substrates, membrane activation, and some proteolytic activities. It also shows a series of three head-to-tail cysteine-rich repeats within its catalytic domain. These inserts resemble the collagen-binding type II repeats of fibronectin and are required to bind and cleave collagen and elastin. Like other proteolytic enzymes, MMP-9 is first synthesized as inactive proenzyme or zymogens. Activation of proMMP-9 is mediated by plasminogen activator/plasmin (PA/plasmin) system. The regulation of MMP-9 activity is also controlled through TIMP-3.
Expression	MMP-9 expression is regulated by several cytokines and growth factors, including interleukins, interferons, EGF (Epidermal growth factor), NGF (Nerve growth factor), basic FGF (Fibroblast growth factor), VEGF (Vascular endothelial growth factor), PDGF (Platelet derived growth), TNF-a (Tumor necrosis factor), TGF-b (Tranforming growth factor), the extracellular matrix metalloproteinase inducer EMMPRIN and also osteopontin. Many of these stimuli induce the expression and/or activation of c-fos and c-jun proto-oncogene products, which heterodimerize and bind activator protein-1 (AP-1) sites within of MMP9 gene promoters.
Localisation	Peri/extracellular
Function	Primary function is degradation of proteins in the extracellular matrix. It proteolytically digests decorin, elastin, fibrillin, laminin, gelatin (denatured collagen), and types IV, V, XI and XVI collagen and also activates growth factors like proTGFb and proTNFa. Physiologically, MMP-9 in coordination with other MMPs, play a role in normal tissue remodeling events such as neurite gowth, embryonic development, angiogenesis, ovulation, mammary gland involution and wound healing. MMP-9 with other MMPs is also involved in osteoblastic bone formation and/or inhibits osteoclastic bone resorption.
Homology	Homology in amino acid sequence is seen with the other members of Metalloproteinase family especially with MMP-2.

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