Intermediate filaments

Intermediate filaments are protoplasmic strands made up of a diverse range of proteins. They are all around 10 nanometres in diameter, but the monomers proteins which polymerize to form the strands have very variable structures and molecular weights. At least 5 subclasses of protein are recognized, all sharing regions of homologous structure:

• keratins; found in epithelial cells such as keratinocytes
• vimentins; endothelial and smooth muscle cells
• desmins; muscle cells
• glial fibrillary acidic protein; in glial cells, polymerize to produce glial filaments
• neurofilament proteins; in neurons, polymerize to produce neurofilament

Intermediate filaments can bind rigidly to other cellular structures and, unlike microtubules and microfilaments, they do not undergo rapid turnover. Hence, in the form of extensive networks throughout the cell, intermediate filaments provide a relatively permanent endoskeleton to counter physical stresses.