Visualization of a 21-nm axial periodicity in shadowed keratin filaments and neurofilaments.

Open Access
Publisher Website
Google Scholar
Abstract
Unidirectional and rotary shadowing techniques were applied in studying the surface structure of 2 types of intermediate filaments. Keratin filaments and neurofilaments demonstrate a .apprx. 21-nm axial periodicity which probably indicates the helical pitch of the outer shell of the filament. Analysis of unidirectionally shadowed keratin showed that the helix is left-handed. The observation of a left-handed of 21-nm pitch supports the 3-stranded protofilament model of Fraser, Macrae and Suzuki, and indicates that keratin filaments probably consist of 10 3-stranded protofilaments surrounding a core of 3 such protofilaments, as predicted by models based on X-ray diffraction of hard keratin filaments. Neurofilaments do not demonstrate an easily identifiable hand, so their consistency with the model is, as yet, uncertain.