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QuickView for Intermediate filament protein, conserved site (biogroup)
- Description:
- Intermediate filaments (IF) 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 six 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: 'Orphan' IF proteins, which are more distant in terms of their amino acid sequences. All IF proteins are structurally similar in that they consist of: a centralrod domain comprising some 300 to 350 residues which is arranged in coiled-coiled alpha-helices, with at least two short characteristic interruptions; aN-terminal non-helical domain (head) of variable length; and a C-terminaldomain (tail) which is also non-helical, and which shows extreme lengthvariation 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. The IF rod domain is approximately 310 residues long in all cytoplasmic IF proteins andclose to 350 residues in the nuclear ones. The IF rod domain exhibits aninterrupted alpha-helical conformation and reveals apronounced seven-residue periodicity in the distribution of apolar residues.The heptad periodicity within the rod domain is interrupted in several places,which generates four consecutive alpha-helical segments: 1A and 1B, whichtogether form the so-called coil 1, and 2A and 2B, which form coil 2. The fouralpha-helical segments are interconnected by relatively short, variablelinkers L1, L12 and L2.IF proteins have a very strong tendency to dimerize via the formation of analpha-helical coiled coil (CC) by their rod domains.This entry represents a conserved region situated at the very end of the 2B segment, which is critically involved in specific dimer-dimer interactions within the mature filament.
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