Figure 1 - Generalized structure of cytoplasmic intermediate-filament proteins compared to lamins.

Intermediate-filament proteins have a conserved domain structure consisting of a variable globular head domain, a central -helical coiled-coil dimerization domain consisting of four coiled coils, based on heptad repeats, interrupted by flexible linker domains and a variable globular tail domain. The coiled-coil domains are termed 1A, 1B, 2A and 2B, respectively. The linker domains are non-helical. The major differences between lamins and vertebrate cytoplasmic intermediate filaments are that: first, the head domains are very short (about 33 amino acids); second, there is a six-heptad extension of coil 1B; and third, the globular tail domain is usually characterized by possession of a nuclear localization signal sequence and a site for carboxyl methylation, farnesylation and proteolytic cleavage (CaaX).