ERK3/4 MAP kinase
InterPro Protein Domain record
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<p>Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process. Protein kinases fall into three broad classes, characterised with respect to substrate specificity [<cite idref="PUB00005115"/>]:</p><p> <ul> <li>Serine/threonine-protein kinases</li><li>Tyrosine-protein kinases</li><li>Dual specific protein kinases (e.g. MEK - phosphorylates both Thr and Tyr on target proteins)</li> </ul> </p><p>Protein kinase function has been evolutionarily conserved from <taxon tax_id="562">Escherichia coli</taxon> to human [<cite idref="PUB00020114"/>]. Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation [<cite idref="PUB00015362"/>]. Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins. The catalytic subunits of protein kinases are highly conserved, and several structures have been solved [<cite idref="PUB00034898"/>], leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases [<cite idref="PUB00034899"/>].</p><p>MAP (Mitogen Activated Protein) kinases participate in kinase cascades,whereby at least 3 protein kinases act in series, culminating in activationof MAP kinase [<cite idref="PUB00011603"/>]. MAP kinases are activated by dual phosphorylationon both tyrosine and threonine residues of a conserved TXY motif.</p><p>ERKs (Extracellularly Regulated Kinases) belong to the family of MAPkinases. ERK 3 and 4, however, have no more similarity to ERK 1 and 2 thando the other major classes of MAP kinase, JNK and p38. ERK3 isconstitutively located in the nucleus, despite the lack of a traditionalnuclear localisation signal [<cite idref="PUB00011604"/>]. It is unique among MAP kinases incontaining in its activation loop only a single phosphorylation site (serine189) - other MAP kinases have the sequence TXY in this loop, but ERK3contains SEG, with glycine in place of tyrosine.</p><p>ERK3 has no homologues in nematode or yeast genomes, indicating that it mayhave arisen from a relatively late gene duplication. Its structure,based on similarity to ERK2, contains segregated alpha and beta regions.</p>
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