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, microtubule-associating proteins, nuclear laminin B., SPTAN1, vimentin and ITGB4.
Studies employing a plectin knockout mouse have shed light on the functions of plectin. Pups died 2–3 days after birth, and these mice exhibited marked skin abnormalities, including degeneration of keratinocytes. Skeletal and cardiac muscle tissues were also significantly affected.
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