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MECP2 is the key modificator of eukaryotic genomes and has a crucial part in mammalian development.
Human proteins MECP2, MBD1, MBD2, MBD3, and MBD4 form a family of nuclear proteins linked by the existence in each of a methyl-CpG binding domain (MBD). Each one of these proteins, with the exception of MBD3, can bind specifically to methylated DNA. In addition, MECP2, MBD1 and MBD2 can inhibit transcription from methylated gene promoters. Unlike other MBD family members, MECP2 is X-linked and subject to X inactivation. MECP2 is expendable in stem cells, but is vital for embryonic development. MECP2 gene mutations are the cause of most cases of Rett syndrome, a progressive neurologic developmental disorder and one of the most common reasons of mental retardation in females.

Dimethylarginine dimethylaminohydrolase 1, is a part of the Dimethylarginine Dimethylaminohydrolase gene family. DDAH1 participates in nitric oxide generation by regulating cellular concentrations of methylarginines, that in turn inhibit nitric oxide synthase activity. Deficiency of DDAH1 results in ADMA (asymmetric dimethylarginine) increase and a decrease in cGMP generation.

MGMT is an enzyme that repairs O-6-methylguanine, a mutagenic DNA base damaged by endogenous and environmental alkylating agents and takes part in the cellular defense against the biological effects of O-6-methylguanine in DNA. MGMT repairs alkylated guanine in DNA by stoichiometrically transferring the alkyl group at the O-6 position to a cysteine residue in the enzyme. abnormal MGMT expression correlates with the prognosis in human solid cancers. MGMT decrease of expression is correlated with methylation. The human MGMT is a negative regulator of estrogen receptor-mediated transcription upon alkylation DNA damage. MGMT promoter hypermethylation plays an important role in the early steps of colorectal carcinogenesis. Abnormal promoter hypermethylation of MGMT gene is associated with oral squamous cell carcinomas.

Malate dehydrogenase (EC1.1.1.37) is an enzyme in the citric acid cycle that catalyzes the conversion of malate into oxaloacetate (using NAD+) and vice versa (this is a reversible reaction). Malate dehydrogenase is not to be confused with malic enzyme, which catalyzes the conversion of pyruvate using NADPH.
Malate dehydrogenase is also involved in gluconeogenesis, the synthesis of glucose from smaller molecules. Pyruvate in the mitochondria is acted upon by pyruvate carboxylase to form oxaloacetate, a citric acid cycle intermediate. In order to get the oxaloacetate out of the mitochondria, malate dehydrogenase reduces it to malate, and it then traverses the inner mitochondrial membrane. Once in the cytosol, the malate is oxidized back to oxaloacetate by cytosolic malate dehydrogenase. Finally, phosphoenol-pyruvate carboxy kinase (PEPCK) converts oxaloacetate to phosphoenol pyruvate.

Maltose Binding Protein is a member of the maltose/maltodextrin system of E.Coli, which is accountable for the uptake and efficient catabolism of maltodextrins. The maltose/maltodextrin is a complex regulatory and transport system involving many proteins and protein complexes.
MBP elevates the yield of its fusion partner in many cases and is often able to promote the solubility of polypeptides to which it is fused.

Methionine sulfoxide reductase B (MsrB) from Escherichia coli is a member of the msrB Met sulfoxide reductase family. The E.coli msrB carries out the reduction of methionine-R-sulfoxide to methionine. msrB possess a metal binding site composed of 2 CXXC motifs. The bound metal (zinc or iron) may stabilize the conformation of the enzymes.

MAGEA4 is part of the MAGEA family, which directs the expression of tumor antigens that are identified on a human melanoma by autologous cytolytic T lymphocytes (CTL). MAGEA4 participates in embryonal development and tumor transformation or aspects of tumor progression. MAGEA4 is expressed in many tumors of several types, such as melanoma, head and neck squamous cell carcinoma, lung carcinoma and breast carcinoma, but not in normal tissues except for testes and placenta.

Matrix metalloproteinases are a family of zinc and calcium-dependent endopeptidases that break down extracellular matrix proteins. The MMP9 is secreted as a 92kDa zymogen. Cleavage of ProMMP-9 results in the active enzyme, having a molecular weight of approximately 82kDa. MMP9 is composed of the following domains: a gelatin-binding domain consisting of three fibronectin type II units, a catalytic domain containing the zinc-binding site, a proline-rich type V collagen-homologous domain and a hemopexin-like domain. MMP9 is produced by the several cell types: monocytes, macrophages, neutrophils, keratinocytes, fibroblasts, osteoclasts and endothelial cells. MMP9 is involved in inflammatory responses, tissue remodeling, wound healing, tumor growth and metastasis. MMP9 may also play an important part in local proteolysis of the extracellular matrix and in leukocyte migration, as well as in bone osteoclastic resorption. MMP9 cleaves type IV and type V collagens into large C-terminal three quarter fragments and shorter N-terminal one quarter fragments. MMP9 can also degrade fibronectin but not laminin or Pz-peptide.
MMP9 defects may be a cause of susceptibility to intervertebral disc disease (IDD), also known as lumbar disk herniation (LDH).

melA is a member of the glycosyl hydrolase 4 family. melA catalyze the hydrolysis of saccharides containing o-1,6,-galactoside bonds. melA catalyze the same reaction in E.coli, human and yeast but is found in different cellular sections: The E.coli melA is a cytoplasmic protein and the human and yeast melA are secretory proteins. Thus, even though the active enzyme from all three species has almost an equal molecular weight, structural resemblances, as well as dissimilarities, are probable.

Methionine sulfoxide reductase B3 (MSRB3) is a member of the methionine sulfoxide reductases (MSR) family proteins. MSRB3 catalyzes the reduction of methionine sulfoxide to methionine. The MSRB3 enzyme acts as a monomer and requires zinc as a cofactor. MSRs are thought to defend against reactive oxygen species-induced oxidative damage in various organs, including the most environmentally exposed organ, the human skin. MSRB3 has a vital role in cold tolerance by eliminating MetO and ROS which accumulate at the ER during cold acclimation.

Meprin A subunit alpha (MEP1A) is a single-pass type I membrane protein which is a member of the peptidase M12A family. MEP1A is abundantly expressed in the kidney and intestinal epithelial cells, is secreted into the urinary tract and intestinal lumen, and found in leukocytes and cancer cells under certain conditions. MEP1A is capable of proteolytically degrading extracellular matrix proteins, proteolytically processing bioactive proteins, and has a role in inflammatory processes.

MMP-1 can break down a wide range of substrates including types I, II, III, VII, VIII, and X collagens as well as L-Selectin, pro-TNF, IL-1?, IGFBP-3, IGFBP-5, casein, gelatin, ?1 antitrypsin, myelin basic protein, pro-MMP2 and pro-MMP9. A significant function of MMP-1 is the degradation of fibrillar collagens in extracellular matrix remodeling. MMP-1 is expressed in fibroblasts, keratinocytes, endothelial cells, monocytes and macrophages. MMP1 can be divided into a number of distinct domains: a prodomain which is cleaved on activation, a catalytic domain containing the zinc binding site and a short hinge region with a carboxyl terminal domain. MMP1 is part of a cluster of MMP genes which localize to chromosome 11q22.3.

MVK is a member of the GHMP kinase family. Mevalonate is a vital mediator, and MVK an important early enzyme, in isoprenoid and sterol synthesis. MVK deficiency can result in gene mutation associated with Mevalonic aciduria, an illness which causes psychomotor retardation, failure to thrive hepatosplenomegaly, anemia and frequent febrile crises. Mutations in this gene also cause hyperimmunoglobulinaemia D and sporadic fever syndrome, in which the person suffers from recurrent episodes of fever related with lymphadenopathy, skin rash, gastrointestinal dismay and arthralgia.

METTL21A, which is a part of the methyltransferase superfamily, is a Protein-lysine methyltransferase that in vitro methylates HSPA1, HSPA5 and HSPA8.

MAGE belongs to the MAGE gene family, that comprises 12 known genes, of which 6 are expressed in tumors. The Melanoma-associated antigen 3 genes were originally isolated from different kinds of tumors, and based on their virtually limited tumor-specific expression in adult tissues, they were used as targets for cancer immunotherapy. MAGEA3 is a tumor-specific antigen extensively expressed in solid and hematologic malignancies, but not in normal tissues, with the exclusion of testis and placenta. Consequently, MAGEA3 is an outstanding candidate tumor antigen.

MAF1 resembles Maf1 which is a Saccharomyces cerevisiae – a highly conserved protein in eukaryotic cells, localized to the nucleus. MAF1 Interacts with BRF2, MAF1 and functions as a mediator for signals which explicitly inhibit RNA polymerase III (Pol III) activity by inhibiting the association of TFIIIB to DNA. MAF1 reacts to modifications in the cellular environment and represses pol III transcription.

MAP3K12 Binding Inhibitory Protein 1 (MBIP) is a part of the ATAC complex which consists of histones H3 and H4 with a histone acetyltransferase activity. MBIP inhibits the MAP3K12 activity in order to induce the activation of the JNK/SAPK pathway.

Dual specificity mitogen-activated protein kinase kinase 3 (MAP2K3) is a dual specificity protein kinase which is a member of the MAP kinase kinase family. MAP2K3 is activated by mitogenic and environmental stress, and participates in the MAP kinase-mediated signaling cascade. MAP2K3 phosphorylates and consequently activates MAPK14/p38-MAPK.

Matrix metalloproteinase-2 (MMP-2) is involved in endometrial menstrual breakdown, regulation of vascularization and the inflammatory response. MMP-2 contains a number of distinct domains: a prodomain that is cleaved upon activation; a catalytic domain containing the zinc binding site; a fibronectin like domain believed to have a role in substrate targeting; and a carboxyl terminal (hemopexin like) domain containing 2 N-linked glycosylation. The MMP-2 can degrade an extensive array of substrates including type IV, V, VII and X collagens as well as gelatin type I. In addition, MMP-2 interacts with THBS2, TIMP2, Thrombospondin 1, CCL7 and TIMP4. MMP-2 autocatalytic cleavage in the C-terminal generates the anti-angiogenic peptide, PEX. This process seems to be made possible by binding integrinv/beta3. Defects in the MMP-2 are the cause of Torg-Winchester syndrome (TWS), aka multicentric osteolysis nodulosis and arthropathy (MONA).

MMP-3 enzyme is also known as Stromelysin-1or as Transin-1 which hydrolyzes natural collagen at physiological pH and temperature. It dissolves the intervertebral nucleus pulposus and annulus fibrosus of Herniated Lumbar Intervertebral Disk . MMP-3 hydrolyzes components of the extracellular matrix like proteoglycan, laminin, fibronectin, gelatin and collagen types III, IV and IX. It also activates pro-MMP-9 and pro-MMP-8 and superactivates plasmin activated MMP-1. MMP-3 is secreted as a latent proenzyme and is activated by a variety of proteinases, e.g. plasmin, trypsin, chymotrypsin, cathepsin G or human neutrophil elastase. MMP-3 was found to be capable of activating the precursor of IL1-beta.

MSRB2 is a member of the methionine sulfoxide reductases(MSRs) family which are antioxidant repair enzymes. MSRB2 protein catalyzes the decrease of free and protein-bound methionine sulfoxide to methionine. MSRB2 has a part in protecting against oxidative stress in numerous organs.

Mediator Complex Subunit 20 (MED20) is a subunit of the Mediator complex, which is a multiprotein coactivator of RNA transcription that interacts with DNA-bound transcriptional activators, RNA polymerase II, and general initiation factors. The Mediator functions as a link to transmit information from gene-specific regulatory proteins to the basal RNA polymerase II transcription apparatus. Mediator is recruited to promoters by direct interactions with regulatory proteins and functions as a scaffold for the compilation of a functional preinitiation complex with RNA polymerase II and the general transcription factors.

MYC Induced Nuclear Antigen, also known as MINA is an oxygenase which can function both as a histone lysine demethylase and a ribosomal histidine hydroxylase. MINA is involved in the demethylation of trimethylated Lys-9 on histone H3 (H3K9me3), leading to an increase in ribosomal RNA expression. MINA also catalyzes the hydroxylation of 60S ribosomal protein L27a on His-39. In addition, MINA plays a significant role in cell growth and survival. MINA is implicated in ribosome biogenesis, probably in the duration of the assembly process of pre-ribosomal particles.