Адам ағзасындағы плектин ақуызының құрылымы мен функциясы

Mammalian protein found in Homo sapiens

Plectin is a giant protein found in nearly all mammalian cells which acts as a link between the three main components of the cytoskeleton: actin microfilaments, microtubules and intermediate filaments. In addition, plectin links the cytoskeleton to junctions found in the plasma membrane that structurally connect different cells. By holding these different networks together, plectin plays an important role in maintaining the mechanical integrity and viscoelastic properties of tissues.

Plectin can exist in cells as several alternatively spliced isoforms, all around 500 kDa and >4000 amino acids. The structure of plectin is thought to be a dimer consisting of a central coiled coil of alpha helices connecting two large globular domains (one at each terminus). These globular domains are responsible for connecting plectin to its various cytoskeletal targets. The carboxy terminal domain is made of 6 highly homologous repeating regions. The subdomain between regions five and six of this domain is known to connect to the intermediate filaments cytokeratin and vimentin. At the opposite end of the protein, in the N terminal domain, a region has been defined as responsible for binding to actin. In 2004, the exact crystal structure of this actin binding domain (ABD) was determined in mice and shown to be composed of two calponin homology (CH) domains. Plectin is expressed in nearly all mammalian tissues. In cardiac muscle and skeletal muscle, plectin is localized to specialized entities known as Z discs. Plectin binds several proteins, including vinculin, DES, actin, fodrin, vimentin and ITGB4. Through the use of gold immunoelectron microscopy, immunoblotting and immunofluorescence experiments plectin has been found to associate with all three major components of the cytoskeleton. In muscle, plectin binds to the periphery of Z discs, Plectin also functions to link cytoskeleton to intercellular junctions, such as desmosomes and hemidesmosomes, which link intermediate filament networks between cells. Plectin has been revealed to localize to the desmosomes and in vitro studies have shown that it can form bridges between the desmosome protein, desmoplakin and intermediate filaments. In hemidesmosomes plectin has been shown to interact with the integrin β4 subunits of the hemidesmosome plaque and function in a clamp like manner to link the intermediate filament cytokeratin to the junction.