Local mechanical disruption of neurofilaments with the atomic force microscope

Neurofilaments reassembled from purified NF-L were investigated by atomic force microscopy. Filaments adsorbed well to both mica and unmodified silicon surfaces. Air-dried filaments imaged by ambient tapping mode AFM revealed the well-known 21-nm repeat and had a morphology similar to that seen by electron microscopy. However, air-dried filaments appeared significantly compressed and measured only 3-4 nm in thickness (from the substrate). Filaments imaged by tapping mode in solution did not show the 21-nm repeat but were 10-12 to- nm thick, in good agreement with the known dimensions of these filaments. Repeated scanning of the reassembled NF- L.filaments produced disruptions in filaments and loss of segments internally and at the ends. This segmental disruption appears to be caused by a mechanical interaction of the AFM tip with the sample. Therefore, the AFM may provide a novel tool for investigating mechanical stability of neurofilaments and other intermediate filaments.