Figure 3. Structural polymorphism along keratin filaments.

Computationally reconstituted filaments provide a realistic view of the KIFs at higher resolution (see Materials and methods). (A – D) Scale bar: 20 nm. (A) A typical keratin filament consisting of various regions with helical and straight-line patterns, indicated by red and yellow lines, respectively. (B) Keratin filament displaying diameter fluctuations. Areas of increased diameter are indicated (blue arrows). (C) Keratin filament showing helical patterns exhibiting different pitches, indicating modulations within the ice layer. Short repeating patterns (purple) indicate higher tilt angles in comparison to longer repeating patterns of in-plane filament stretches (green). (D) Keratin filament displaying diameter fluctuations. Areas of decreased diameter are indicated (orange arrows). (E) A collage of six computationally reconstituted keratin filaments showing structural diversity (total n=4460 filaments).

Figure 3—figure supplement 1. Reconstitution of keratin filaments.

(A) Back-mapping of class averages onto the original filaments allowed us to assemble reconstituted, non-straightened keratin filaments in the original cryo-EM micrographs. Reconstituted filaments are displayed in white. (B) Keratin segments that originate from the same filament are plotted as columns of circles. The filaments are composed of helical (blue) and straight (red) class averages. Representative reconstituted filaments are shown and their composition by helical and straight classes is indicated. (C) Examples of reconstituted keratin filaments revealing the extensive heterogeneity in filament architecture.