Intermediate Filament Structure

TL;DR: Together with actin microfilaments and microtubules (MT), intermediate filaments constitute one of the three major systems of protein filaments that form the cytoskeletal networks of virtually all eukaryotic cells.

Abstract: Together with actin microfilaments and microtubules (MT), intermediate filaments (IF, or “intermediate-sized” filaments) constitute one of the three major systems of protein filaments that form the cytoskeletal networks of virtually all eukaryotic cells. However, unlike actin and tubulin, which are highly conserved molecules, IF proteins make up a notably diverse family, whose molecular weights range from ~ 44k to ~ 120k. The helical packing arrangements of protein subunits in actin filaments and MT have long been known, and their quaternary structures have been found (like their primary sequences) to be resistant to evolutionary divergence. In contrast, a conclusive determination of the molecular packing in any kind of IF remains to be achieved, although considerable progress has been made (see Fraser et. al., this volume). Consequently, the extent to which different IF are structurally related—apart from their having roughly similar diameters—has been unclear.