Sandbox Reserved 468: Difference between revisions

MMP-1 belongs to a family of enzymes known as Matrix metalloproteinases (MMPs). These enzymes are known as zinc-dependent endopeptidases because of the zinc ions involved in the catalytic site. The MMPs belong to a larger family of proteases known as the metzincin superfamily. MMPs are capable of degrading all kinds of extracellular matrix proteins as well as process a number of other bioactive molecules. They are known to be involved in the cleavage of cell surface receptors, the release of apoptotic ligands (such as the FAS ligand), and chemokine/cytokine in/activation. MMPs are also thought to play a major role on cell behaviors such as cell proliferation, migration (adhesion/dispersion), differentiation, angiogenesis, apoptosis,host defense, embryonic development, reproduction, and tissue remodeling. MMPs are also involved in disease processes, such as arthritis and metastasis [5].  

MMP's were first described in vertebrates in 1962 but have also been found in invertebrates and plants. They are distinguished from other endopeptidases by their dependence on metal ions as cofactors, their ability to degrade extracellular matrix, and their specific evolutionary DNA sequence. MMPs are secreted as inactive proproteins which is later activated when cleaved by extracellular proteases [2][3].

The structure of MMP-1, just like the other members of matrix metalloproteinases family, is formed by different subsections. The structure consists of a <scene name='Sandbox_Reserved_468/Catalytic_domain/2'>Catalytic Domain</scene>, a Linker Region and the <scene name='Sandbox_Reserved_468/Linker_region/1'>Hemopexin-like domain</scene>. The structure was determined by using X-ray crystallography and NMR [2][3].

The Catalytic Domains of all MMPs share very similar characteristics, having a general shape of oblate ellipsoid with a diameter of ~40Å. The <scene name='Sandbox_Reserved_468/Catalytic_domain/2'>Catalytic Domain</scene> of MMP-1 is composed of five highly twisted β-strands, three α-helix and a total of eight loops, enclosing a total of five metal ions, three Ca2+ and two Zn2+, one of which with catalytic role [2]. The Catalytic Domain (CAT) of MMP-1 starts with the F100 as the first amino-acid of the N-terminal loop of the CAT domain. This is different from the first published x-ray structure of the CAT domain was showed the truncated form of this domain, where the first 7 amino-acids are not present [6].

In MMPs the catalytic domain is followed by a stretch of 15–65 amino acid residues referred to as the linker or the hinge region. This region is rich in proline residues and replacement of those with alanine drastically reduced the collagenolytic activity of MMP-8 (neutrophil collagenase),19 indicating that the presence of the correct linker structure is important for collagenolysis [4].

There is not a generally accepted mechanism of action for this enzyme but there are three possible catalytic mechanisms published. In the first mechanism, Browner M.F. and colleagues proposed the base-catalysis mechanism, carried out by the conserved glutamate residue and the Zn2+ ion. In the second mechanism, the Matthews-mechanism, Kester and Matthews suggested an interaction between a water molecule and the Zn2+ ion during the acid-base catalysis. In the third mechanism, the Manzetti-mechanism, Manzetti Sergio and colleagues provided evidence that a coordination between water and zinc during catalysis was unlikely, and suggested a third mechanism wherein a histidine from the HExxHxxGxxH-motif participates in catalysis by allowing the Zn2+ ion to assume a quasi-penta coordinated state, via its dissociation from it. In this state, the Zn2+ ion is coordinated with the two oxygen atoms from the catalytic glutamic acid, the substrate's carbonyl oxygen atom, and the two histidine residues, and can polarize the glutamic acid's oxygen atom, proximate the scissile bond, and induce it to act as reversible electron donor. This forms an oxyanion transition state. At this stage, a water molecule acts on the dissociated scissile bond and completes the hydrolyzation of the substrate.

Research has shown that MMP-1 may have many medical implications. MMP-1 plays an important role in many physiologic processes such as development, tissue morphogenesis, wound repair and the remodeling of collagenous extracellular matrix. The enzyme is expressed by over 30 different cells. Collagen serves as a structural scaffold and a barrier between tissues, and thus collagen catabolism (collagenolysis) is required to be a tightly regulated process in normal physiology. In turn, the destruction or damage of collagen during pathological states plays a role in tumor growth and invasion, cartilage degradation, or atherosclerotic plaque formation and rupture [4].