ENTROPIC EXCLUSION BY NEUROFILAMENT SIDEARMS - A MECHANISM FOR MAINTAINING INTERFILAMENT SPACING

A long-range repulsive force near isolated neurofilaments was detected by exclusion of large molecules and by direct force measurements with atomic force microscopy, Adsorption of isolated native neurofilaments to a solid substrate in a high-salt solution (170 mM NaCl), in the pr esence of coisolating contaminants, shows that the contaminants are ex cluded from a zone that extends 50-100 nm from the core of the filamen t. Force-distance measurements by AFM show the presence of a weak repu lsive force that extends >50 nm from the core of the filament; this re pulsive force is absent in homopolymers of neurofilament L or trypsini zed native filaments that lack the long sidearms present in native fil aments. These results suggest that neurofilament sidearms form an entr opic brush, thereby providing a mechanism for maintaining interfilamen t spacing.