Intermediate filaments

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Intermediate filaments ( Filamenta intermedialia ) are structures made of proteins in the cytoplasm of a cell , which serve to increase the mechanical stability of the cell. In addition to microtubules and microfilaments, they are among the main structural components of the cytoskeleton . The name comes from the fact that they are around 10 nanometers in diameter between the microfilaments (7 nm) and the microtubules (20 to 30 nm). There are no intermediate filaments in plants .

construction

Structure of an intermediate filament

A single monomer , the subunit of the intermediate filaments, is about 48 nm long and very thin. The monomer has globular domains at both ends that are type-specific, i.e. they can differ from protein to protein. A coiled coil dimer consists of two parallel monomers wound around themselves like ropes. Several of these dimers are antiparallel and slightly shifted by non-covalent bonds to one another to form tetramers. Many of these tetramers in turn form a rope-like filament with a tetramer in the center and seven tetramers wound around it with a total diameter of approx. 10 nm.

The intermediate filaments are connected to one another to form larger bundles ( tonofibrils ) by specific proteins ( intermediate filament-associated proteins , e.g. desmoplakin ) . These proteins also serve to connect the intermediate filaments to the other elements of the cytoskeleton.

Types

There are currently six types of intermediate filaments, some of which are still unclassified, so that up to nine types are conceivable. Some are tissue-specific, lamines are found in all cells.

Type Representative Occurrence
1 (acidic keratin) acidic keratin Epithelia
2 (basic keratins) basic keratin Epithelia
3 ( Desmine ) GFAP (glial fibrillar acidic protein)
Desmin
Vimentin
peripherin
Glial cells , astrocytes,
muscle
cells, cells of mesenchymal origin,
peripheral neurons
4th α-internexin CNS during development
5 ( lamines ) Lamin A
Lamin B
Lamin C
Nucleus
nucleus
nucleus
6 ( neurofilaments ) NF-L
β-internexin
NF-M
NF-H
nestin
Neurons
neurons
neurons
neurons
neuroepithelial stem cells

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