Electron microscopy supports a fibrous substructure for lens intermediate filaments

Area of Science:

• Cell Biology
• Biophysics

Background:

• Intermediate filaments are crucial cytoskeletal components.
• Understanding their substructure is key to cell mechanics and function.

Purpose of the Study:

• To elucidate the detailed substructure of intermediate filaments from bovine lens cortical fiber cells.
• To compare native and reconstituted filaments.

Main Methods:

• Electron microscopy (negative staining, positive staining of sections).
• Regeneration of synthetic filaments from purified subunits.

Main Results:

• Filaments from various sources showed identical morphology, except for one subunit.
• Filaments are solid cylinders with helical arrangement of two 5nm strands.
• Each strand comprises two 2nm protofilaments in a right-handed helix (11.6 nm periodicity).
• Filament diameter (8-14.8 nm) correlates linearly with strand helical angle.

Conclusions:

• Bovine lens intermediate filaments possess a conserved, complex helical substructure.
• The protofilament arrangement dictates filament diameter and properties.