Cryo-Electron Microscopy of Trichocyte (Hard Alpha-Keratin) Intermediate Filaments Reveals a Low-Density Core

The study investigated the structure of trichocyte intermediate filaments (IF) from rat vibrissae and human hair follicles using cryo-electron microscopy. It was found that these filaments had a mass-per-unit-length of approximately 32 kDa/nm, with some human filaments showing half this density, indicating the presence of two protofibrils instead of four. The cryo-electron micrographs revealed a low-density core of about 3 nm in diameter along the filament axis. Additionally, a minor filament species was observed to be surface-decorated with a helical pitch of 9.3 nm, suggesting the presence of associated proteins, possibly "high-sulfur" proteins, which are prepared for integration into the mature hair's filament-matrix biocomposite.