Assemblies of psoriatic keratin and their relation to normal intermediate filament structures

Protein extracts from normal human epidermis reassemble in vitro into 8-10 nm diameter filaments characteristic of intermediate filaments, whereas extracts from psoriatic epidermal scales reassemble, under identical conditions, into a variety of paracrystalline bundles. Optical diffraction and image analysis of these paracrystalline bundles reveal an axial repeat of 16.5 nm, which subdivides into three bands of 5.5 nm, and a lateral spacing of 5.1 nm. This information, together with available sequence studies of intermediate filaments and biochemical data, suggests that the subunit of psoriatic keratin is made up essentially from the coiled-coil alpha-helical rod domain of the normal keratin subunits, whereas the random coil domains are missing or greatly reduced in size.