Microtubule-associated protein
In addition to tubulin, there are other proteins in the cell that bind to microtubules. These proteins are collectively referred to as microtubule-associated proteins (MAPs). In general, MAPs can increase the stability of microtubules, promote the assembly of microtubules, and regulate the relationship between microtubules and other cellular components. They are essential components to maintain the structure and function of microtubules. MAPs contain two functional regions, one is the basic microtubule binding domain bound to the side of the microtubules, and the other is the acidic protruding binding domain, which is an outwardly protruding filamentous structure that maintains a horizontal bridge with other cell components or skeletal components, cell membranes, etc.). MAPs have microtubule-binding activity and achieve their functions by regulating the phosphorylation and dephosphorylation of specific amino acids. MAPs mainly include MAP1, MAP2, Tau, and MAP4. The first three are mainly in neurons, while MAP4 is present in various cells.
Functions
MAP binds the tubulin subunits that make up microtubules to regulate its stability. A wide variety of MAPs have been identified in many different cell types and found to have a wide range of functions. These include stabilizing and destabilizing microtubules, directing microtubules to specific cellular locations, cross-linking microtubules, and mediating microtubule interactions with other proteins in the cell. Within the cell, MAPs bind directly to tubulin dimers of microtubules. This binding can occur through polymerized or depolymerized tubulin, and in most cases results in the stabilization of the microtubule structure, thereby further promoting polymerization. Usually, the C-terminal domain of MAP interacts with tubulin, while the N-terminal domain can bind to cell vesicles, intermediate filaments, or other microtubules. MAP-microtubule binding is regulated by MAP phosphorylation. This is achieved through the function of microtubule affinity-regulated kinase (MARK) proteins. MARK phosphorylates MAP and detaches it from any bound microtubules. This separation is often associated with instability of the microtubules, causing them to rupture. In this way, the stabilization of microtubules caused by MAP is regulated intracellularly by phosphorylation.
MARK family
MARK is short for Microtubule-associated protein 2 (MAP-2) on Ser/Thr. The gene encodes a protein belonging to the microtubule-associated protein family. This family of proteins is thought to be involved in microtubule assembly, an essential step in neurogenesis. MAP2 stabilizes microtubule (MT) growth by cross-linking MT with intermediate filaments and other MTs. The products of similar genes in rats and mice are neuron-specific cytoskeleton proteins that are rich in dendrites and play a role in determining and stabilizing dendritic shapes during neuron development. Many alternative splicing variants encoding different isoforms have been described.
Functions
MARK binds the tubulin subunits that make up microtubules to regulate its stability. A wide variety of MAPs have been identified in many different cell types and found to have a wide range of functions. These include stabilizing and destabilizing microtubules, directing microtubules to specific cellular locations, cross-linking microtubules, and mediating the interaction of microtubules with other proteins in the cell. Within the cell, MARK bind directly to tubulin dimers of microtubules. This binding can occur through polymerized or depolymerized tubulin, and in most cases results in the stabilization of the microtubule structure, thereby further promoting polymerization. Usually, the C-terminal domain of MARK interacts with tubulin, while the N-terminal domain can bind to cell vesicles, intermediate filaments, or other microtubules. MARK-microtubule binding is regulated by MAP phosphorylation. This is achieved through the function of microtubule affinity-regulated kinase (MARK) proteins. MARK phosphorylates MAP and detaches it from any bound microtubules. This separation is often associated with instability of the microtubules, causing them to rupture. In this way, the stabilization of microtubules caused by MARK is regulated intracellularly by phosphorylation.
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