Dynamic structural order of a low-complexity domain facilitates assembly of intermediate filaments.

The coiled-coil domains of intermediate filament (IF) proteins are flanked by regions of low sequence complexity. Whereas IF coiled-coil domains assume dimeric and tetrameric conformations on their own, maturation of eight tetramers into cylindrical IFs is dependent on either "head" or "tail" domains of low sequence complexity. Here we confirm that the tail domain required for assembly of Tm1-I/C IFs functions by forming labile cross-β interactions. These interactions are seen in polymers made from the tail domain alone, as well as in assembled IFs formed by the intact Tm1-I/C protein. The ability to visualize such interactions in situ within the context of a discrete cellular assembly lends support to the concept that equivalent interactions may be used in organizing other dynamic aspects of cell morphology.