Cytoplasmic intermediate filaments (IF) can be divided into 5 subclasses based on their biochemical properties, immunologic specificity and tissue distribution: keratins in epithelial cells, vimentin, desmin in muscle cells, glial filaments (GFAP) in astrocytes, and neurofilaments in neurons. The different types of intermediate filament proteins share common structural features.
Intermediate filament proteins constitute a highly diverse family of fibrous proteins in metazoans, which assemble into 10-nm-thick filaments in the cytoplasm and the nucleus. The in vitro assembly mechanism have revealed principal differences in the formation of cytoplasmic and nuclear filaments.
Intermediate filaments are a structurally related family of cellular proteins that appear to be intimately involved with the cytoskeleton. The intermediate filaments are built up of rope-like polymers composed of protein subunits with linear a-helical content, and form a complex family of five different groups of filaments, one of which is the epithelial filaments.
Structure
The different sequence data show that the intermediate filament proteins contain a similar alpha-helical domain of conserved length capable of forming coiled-coils.
The common structural motif shared by all IFs is a central alpha-helical 'rod domain' flanked by variable N- and C-terminal domains. The rod domain, the canonical feature of IFs, has been highly conserved during evolution. The variable terminals, however, have allowed the known IFs to be classified into 6 distinct types by virtue of their differing amino acid sequences.
Types
Types I and II
Type III
Type IV
Type V
Type VI
The vimentin, desmin, and glial fibrillary acidic protein genes each contains 8 introns at identical positions, 6 of the introns being located within the regions encoding alpha-helical sequences. A majority of the introns in the less closely related keratin genes occurred at similar or identical positions.
Localization
cytoplasmic filaments
nuclear filaments
intermediate filament-related dermatopathies (fibrillar dermatopathies)
intermediate filament-related myopathies (myofibrillar myopathies)
intermediate filament-related neuropathies
By systems
intermediate filaments in neuropathology
See also
intermediate filament inclusion bodies
intermediate filament polypeptides
interactions with molecular motors
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