Scaffolds localize the signaling reaction to a specific area in the cell, a process that could be important for the local production of signaling intermediates. Localization of signaling components in the cell Ste5 has been proposed to direct mating signaling through the Fus3 MAPK by catalytically unlocking this particular kinase for activation by its MAPKK Ste7. An example is the Ste5 scaffold in the mitogen-activated protein kinase ( MAPK) pathway. Such changes may be able to enhance or inhibit the activation of these signaling proteins. Scaffolds may also be catalytic as interaction with signaling proteins may result in allosteric changes of these signaling components. Additionally, some signaling proteins require multiple interactions for activation and scaffold tethering may be able to convert these interactions into one interaction that results in multiple modifications. A common example of how scaffolds enhance specificity is a scaffold that binds a protein kinase and its substrate, thereby ensuring specific kinase phosphorylation. This assembly may be able to enhance signaling specificity by preventing unnecessary interactions between signaling proteins, and enhance signaling efficiency by increasing the proximity and effective concentration of components in the scaffold complex. Scaffolds assemble signaling components of a cascade into complexes. This particular function is considered a scaffold’s most basic function. Scaffold proteins act in at least four ways: tethering signaling components, localizing these components to specific areas of the cell, regulating signal transduction by coordinating positive and negative feedback signals, and insulating correct signaling proteins from competing proteins. The subsequent endocytosis of the activated receptor and its intracellular trafficking further localizes the signal to other specific areas of the cell. In this case, the receptor’s cytoplasmic domain acts as a scaffold, recruiting signaling proteins and initially localizing the signaling response to the plasma membrane. Upon ligand binding to such receptors, tyrosine autophosphorylation occurs in the receptor’s cytoplasmic domain specifically at sites where SRC homology 2 ( SH2)-domain-containing proteins can bind. The first examples of signaling scaffold proteins were receptor tyrosine kinases like epidermal growth factor receptors and platelet-derived growth factor receptor. 2.4 Insulating correct signaling proteins from inactivation.2.3 Coordinating positive and negative feedback.
2.2 Localization of signaling components in the cell.
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