241 human active and 13 inactive phosphatases in total;
194 phosphatases have substrate data;
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336 protein substrates;
83 non-protein substrates;
1215 dephosphorylation interactions;
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299 KEGG pathways;
876 Reactome pathways;
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last scientific update: 11 Mar, 2019
last maintenance update: 01 Sep, 2023
Cytoplasm, Stress granule Note=Colocalizes with NANOS3 inthe stress granules
Function (UniProt annotation)
Functions in the early steps of protein synthesis byforming a ternary complex with GTP and initiator tRNA Thiscomplex binds to a 40S ribosomal subunit, followed by mRNA bindingto form a 43S pre-initiation complex Junction of the 60Sribosomal subunit to form the 80S initiation complex is precededby hydrolysis of the GTP bound to eIF-2 and release of an eIF-2-GDP binary complex In order for eIF-2 to recycle and catalyzeanother round of initiation, the GDP bound to eIF-2 must exchangewith GTP by way of a reaction catalyzed by eIF-2B
RNA transport from the nucleus to the cytoplasm is fundamental for gene expression. The different RNA species that are produced in the nucleus are exported through the nuclear pore complexes (NPCs) via mobile export receptors. The majority of RNAs, such as tRNAs, rRNAs, and U snRNAs, are transported by specific export receptors, which belong to the karyopherin-beta family proteins. A feature of karyopherins is their regulation by the small GTPase Ran. However, general mRNA export is mechanistically different. Nuclear export of mRNAs is functionally coupled to different steps in gene expression processes, such as transcription, splicing, 3'-end formation and even translation.
Autophagy (or macroautophagy) is a cellular catabolic pathway involving in protein degradation, organelle turnover, and non-selective breakdown of cytoplasmic components, which is evolutionarily conserved among eukaryotes and exquisitely regulated. This progress initiates with production of the autophagosome, a double-membrane intracellular structure of reticular origin that engulfs cytoplasmic contents and ultimately fuses with lysosomes for cargo degradation. Autophagy is regulated in response to extra- or intracellular stress and signals such as starvation, growth factor deprivation and ER stress. Constitutive level of autophagy plays an important role in cellular homeostasis and maintains quality control of essential cellular components.
The endoplasmic reticulum (ER) is a subcellular organelle where proteins are folded with the help of lumenal chaperones. Newly synthesized peptides enter the ER via the sec61 pore and are glycosylated. Correctly folded proteins are packaged into transport vesicles that shuttle them to the Golgi complex. Misfolded proteins are retained within the ER lumen in complex with molecular chaperones. Proteins that are terminally misfolded bind to BiP and are directed toward degradation through the proteasome in a process called ER-associated degradation (ERAD). Accumulation of misfolded proteins in the ER causes ER stress and activates a signaling pathway called the unfolded protein response (UPR). In certain severe situations, however, the protective mechanisms activated by the UPR are not sufficient to restore normal ER function and cells die by apoptosis.
Apoptosis is a genetically programmed process for the elimination of damaged or redundant cells by activation of caspases (aspartate-specific cysteine proteases). The onset of apoptosis is controlled by numerous interrelating processes. The 'extrinsic' pathway involves stimulation of members of the tumor necrosis factor (TNF) receptor subfamily, such as TNFRI, CD95/Fas or TRAILR (death receptors), located at the cell surface, by their specific ligands, such as TNF-alpha, FasL or TRAIL, respectively. The 'intrinsic' pathway is activated mainly by non-receptor stimuli, such as DNA damage, ER stress, metabolic stress, UV radiation or growth-factor deprivation. The central event in the 'intrinsic' pathway is the mitochondrial outer membrane permeabilization (MOMP), which leads to the release of cytochrome c. These two pathways converge at the level of effector caspases, such as caspase-3 and caspase-7. The third major pathway is initiated by the constituents of cytotoxic granules (e.g. Perforin and Granzyme B) that are released by CTLs (cytotoxic T-cells) and NK (natural killer) cells. Granzyme B, similarly to the caspases, cleaves its substrates after aspartic acid residues, suggesting that this protease has the ability to activate members of the caspase family directly. It is the balance between the pro-apoptotic and anti-apoptotic signals that eventually determines whether cells will undergo apoptosis, survive or proliferate. TNF family of ligands activates anti-apoptotic or cell-survival signals as well as apoptotic signals. NGF and Interleukin-3 promotes the survival, proliferation and differentiation of neurons or hematopoietic cells, respectively. Withdrawal of these growth factors leads to cell death, as described above.
Non-alcoholic fatty liver disease (NAFLD) represents a spectrum ranging from simple steatosis to more severe steatohepatitis with hepatic inflammation and fibrosis, known as nonalcoholic steatohepatitis (NASH). NASH may further lead to cirrhosis and hepatocellular carcinoma (HCC). This map shows a stage-dependent progression of NAFLD. In the first stage of NAFLD, excess lipid accumulation has been demonstrated. The main cause is the induction of insulin resistance, which leads to a defect in insulin suppression of free fatty acids (FAAs) disposal. In addition, two transcription factors, SREBP-1c and PPAR-alpha, activate key enzymes of lipogenesis and increase the synthesis of FAAs in liver. In the second stage, as a consequence of the progression to NASH, the production of reactive oxygen species (ROS) is enhanced due to oxidation stress through mitochondrial beta-oxidation of fatty acids and endoplamic reticulum (ER) stress, leading to lipid peroxidation. The lipid peroxidation can further cause the production of cytokines (Fas ligand, TNF-alpha, IL-8 and TGF), promoting cell death, inflammation and fibrosis. The activation of JNK, which is induced by ER stress, TNF-alpha and FAAs, is also associated with NAFLD progression. Increased JNK promotes cytokine production and initiation of HCC.
Hepatitis C virus (HCV) is a major cause of chronic liver disease. The HCV employ several strategies to perturb host cell immunity. After invasion, HCV RNA genome functions directly as an mRNA in the cytoplasm of the host cell and forms membrane-associated replication complexes along with non-structural proteins. Viral RNA can trigger the RIG-I pathway and interferon production during this process. Translated HCV protein products regulate immune response to inhibit the action of interferon. HCV core and NS5A proteins appear to be the most important molecules with regulatory functions that modulate transcription, cellular proliferation, and apoptosis.
Measles virus (MV) is highly contagious virus that leads infant death worldwide. Humans are the unique natural reservoir for this virus. It causes severe immunosuppression favouring secondary bacterial infections. Several MV proteins have been suggested to disturb host immunity. After infection of host lymphoid cells via SLAM, MV inhibits cytokine response by direct interference with host signaling systems. Three proteins (P, V, and C) associate with Jak/STAT proteins in interferon-triggered pathway and other important proteins related to apoptosis. Interaction between MV and host brings about the shift towards a Th2 response by decreasing IL-12 production and induces lymphopenia by suppressing cell proliferation.
Influenza is a contagious respiratory disease caused by influenza virus infection. Influenza A virus is responsible for both annual seasonal epidemics and periodic worldwide pandemics. Novel strains that cause pandemics arise from avian influenza virus by genetic reassortment among influenza viruses and two surface glycoproteins HA and NA form the basis of serologically distinct virus types. The innate immune system recognizes invaded virus through multiple mechanisms. Viral non-structural NS1 protein is a multifunctional virulence factor that interfere IFN-mediated antiviral response. It inhibits IFN production by blocking activation of transcription factors such as NF-kappa B, IRF3 and AP1. NS1 further inhibits the activation of IFN-induced antiviral genes. PB1-F2 protein is another virulence factor that induce apoptosis of infected cells, which results in life-threatening bronchiolitis.
Herpes simplex virus (HSV) infections are very common worldwide, with the prevalence of HSV-1 reaching up to 80%-90%. Primary infection with HSV takes place in the mucosa, followed by the establishment of latent infection in neuronal ganglia. HSV is the main cause of herpes infections that lead to the formation of characteristic blistering lesion. HSV express multiple viral accessory proteins that interfere with host immune responses and are indispensable for viral replication. Among these proteins, the immediate early (IE) gene ICP0, ICP4, and ICP27 are essential for regulation of HSV gene expression in productive infection. On the other hand, ORF P and ORF O gene are transcribed during latency and blocks the expression of the IE genes, thus maintaining latent infection.
While circularization of mRNA during translation initiation is thought to contribute to an increase in the efficiency of translation, it also appears to provide a mechanism for translational silencing. This might be achieved by bringing inhibitory 3' UTR-binding proteins into a position in which they interfere either with the function of the translation initiation complex or with the assembly of the ribosome (Mazumder et al 2001). Translational silencing of Ceruloplasmin (Cp) occurs 16 hrs after its induction by INF-gamma (Mazumder et al., 1997). Although the mechanism by which silencing occurs has not yet been determined, this process is mediated by the L13a subunit of the 60s ribosome and thought to require circularization of the Cp mRNA (Sampath et al., 2003; Mazumder et al., 2001; Mazumder et al., 2003). Between 14 and 16 hrs after INF gamma induction, the L13a subunit of the 60s ribosome is phosphorylated and released from the 60s subunit. Phosphorylated L13a then associates with the GAIT element in the 3' UTR of the Cp mRNA inhibiting its translation
PERK (EIF2AK3) is a single-pass transmembrane protein located in the endoplasmic reticulum (ER) membrane such that the N-terminus of PERK is luminal and the C-terminus is cytosolic. PERK is maintained in an inactive form by interaction of its luminal domain with BiP, an ER chaperone. BiP also binds unfolded proteins and so BiP dissociates from PERK when unfolded proteins accumulate in the ER. Dissociated PERK monomers spontaneously form homodimers and the homodimeric form of PERK possesses kinase activity in its cytosolic C-terminal domain. The kinase specifically phosphorylates the translation factor eIF2alpha at Ser52, resulting in an arrest of translation. Thus translation of proteins targeted to the ER is downregulated. The translation arrest also causes depletion of Cyclin D1, a rapidly turned over protein. The depletion of Cyclin D1 in turn causes arrest of the cell cycle in G1 phase
The ATP-binding cassette (ABC) superfamily of active transporters involves a large number of functionally diverse transmembrane proteins. They transport a variety of compounds through membranes against steep concentration gradients at the cost of ATP hydrolysis. These substrates include amino acids, lipids, inorganic ions, peptides, saccharides, peptides for antigen presentation, metals, drugs, and proteins. The ABC transporters not only move a variety of substrates into and out of the cell, but are also involved in intracellular compartmental transport. Energy derived from the hydrolysis of ATP is used to transport the substrate across the membrane against a concentration gradient. Human genome contains 48 ABC genes; 16 of these have a known function and 14 are associated with a defined human disease (Dean et al. 2001, Borst and Elferink 2002, Rees et al. 2009)
The translation initiation complex forms when the 43S complex binds the mRNA that is associated with eIF4F, eIF4B and eIF4H. eIF4G in the eIF4F complex can directly contact eIF3 in the 43S complex. eIF1A is necessary for the formation of this complex
Binding of the methionyl-tRNA initiator to the active eIF2:GTP complex results in the formation of the ternary complex. Subsequently, this Met-tRNAi:eIF2:GTP (ternary) complex binds to the complex formed by the 40S subunit, eIF3 and eIF1A, to form the 43S complex
The 80S ribosome bound to the mRNA moves along the mRNA molecule from its initial site to the initiation codon and forms a 48S complex, in which the initiation codon is base paired to the anticodon of the Met-tRNAi. Proper recognition of the AUG initiation codon depends on base pairing with the anticodon of the Met-tRNAi and requires eIF1, eIF1A, eIF2 and eIF5
Hydrolysis of eIF2-GTP occurs after the Met-tRNAi has recognized the AUG. This reaction is catalyzed by eIF5 (or eIF5B) and is thought to cause dissociation of all other initiation factors and allow joining of the large 60S ribosomal subunit. The 60S subunit joins - a reaction catalyzed by eIF5 or eIF5B - resulting in a translation-competent 80S ribosome. Following 60S subunit joining, eIF5B hydrolyzes its GTP and is released from the 80S ribosome, which is now ready to start elongating the polypeptide chain
The active eIF2:GTP complex may be formed by direct binding of GTP to free eIF2 or by GDP-GTP exchange on the eIF2:GDP:eIF2B complex. The eIF2:GDP complex binds eIF2B forming an eIF2:GDP:eIF2B intermediate complex. eIF2B is a guanine nucleotide releasing factor required to cause GDP release so that a new GTP molecule can bind and activate eIF2. Phosphorylated eIF2:GDP sequesters all eIF2B as an inactive complex, and thus, reuse of eIF2 is inhibited as a consequence of the tight bond it forms with eIF2B, which prevents nucleotide exchange. Therefore, in the absence of free eIF2B, excess eIF2 remains in its inactive GDP-bound form and protein synthesis slows dramatically