The three-dimensional structure of trichocyte (hard α-) keratin intermediate filaments: The nature of the repeating unit

Recently, the spatial distribution of the crosslinks induced between lysine residues in trichocyte (α-) keratin intermediate filaments (IF) using disulfosuccinimidyl tartrate was analyzed in detail and the results used to provide information about the three-dimensional structure of the IF [Fraser, R.D.B., Parry, D.A.D., 2005. The three-dimensional structure of trichocyte (hard α-) keratin intermediate filaments: features of the molecular packing deduced from the sites of induced crosslinks. J. Struct. Biol. 151, 171-181.] The presence of small amounts of 0 → ±4 crosslinkages between molecular strands four distant in the network implied that the three-dimensional network of interacting molecules must be deeply puckered, but no specific suggestions were made about the nature of the puckering. Whilst it was recognized that there may be more than one type of molecular environment in the structural repeat the initial analysis was confined to the simplest case in which all molecules had the same environment, that is to say the asymmetric unit comprised a single molecule. Further studies reported here suggest that it is likely that the asymmetric unit consists of at least two and possibly as many as four molecules and the implications of this for modeling the structure of trichocyte IF are discussed.