Intermediate filament protein (IPR001664)
Short name: IF
Overlapping homologous superfamilies
- Intermediate filament protein (IPR001664)
- Alpha-internexin (IPR027703)
- Desmin (IPR027698)
- Glial fibrillary acidic protein (IPR027701)
- Intermediate filament, ifa/ifb (IPR016451)
- Keratin, type I (IPR002957)
- Keratin, type II (IPR003054)
- Nestin (IPR031211)
- Neurofilament heavy polypeptide (IPR033183)
- Neurofilament light polypeptide (IPR027692)
- Neurofilament medium polypeptide (IPR027697)
- Syncoilin (IPR027702)
- Synemin (IPR030634)
- Vimentin (IPR027699)
Intermediate filaments (IF) [PMID: 8771189, PMID: 3052284, PMID: 2183847] are proteins which are primordial components of the cytoskeleton and the nuclear envelope. They generally form filamentous structures 8 to 14 nm wide.
IF proteins are members of a very large multigene family of proteins which has been subdivided in five major subgroups:
- Type I: Acidic cytokeratins.
- Type II: Basic cytokeratins.
- Type III: Vimentin, desmin, glial fibrillary acidic protein (GFAP), peripherin, and plasticin.
- Type IV: Neurofilaments L, H and M, alpha-internexin and nestin.
- Type V: Nuclear lamins A, B1, B2 and C.
- Type VI: Nestin.
All IF proteins are structurally similar in that they consist of: a central rod domain comprising some 300 to 350 residues which is arranged in coiled-coiled alpha-helices, with at least two short characteristic interruptions; a N-terminal non-helical domain (head) of variable length; and a C-terminal domain (tail) which is also non-helical, and which shows extreme length variation between different IF proteins.
While IF proteins are evolutionary and structurally related, they have limited sequence homologies except in several regions of the rod domain.