Characterization of a Class of Cationic Proteins That Specifically Interact with Intermediate Filaments

We describe a class of cationic structural proteins that associate specifically with intermediate filaments (IF) but not with other types of cytoskeletal proteins. These proteins, for which the term filaggrin is introduced, are isolated from the stratum corneum of mammalian epidermis. They are species-distinct proteins; for example, rat and mouse filaggrin have different molecular weights and amino acid compositions, but are nevertheless chemically and functionally very similar. They interact in vitro with the IF of several different types of cells to form large fibers or macrofibrils in which many IF are highly aligned in parallel arrays. Stoichiometric analyses suggest that two molecules of filaggrin bind to each three-chain building block of the IF, possibly by ionic interactions with the coiled-coil α -helical regions of the IF.