Acceleration of bovine neurofilament L assembly by deprivation of acidic tail domain

Abstract

Functions of the tail region of neurofilament L have, to date, not been clearly elucidated. Bovine neurofilament L was cleaved into tail‐less neurofilament L (50 kDa) and a tail fragment (19 kDa), by thrombin. Tail‐less neurofilament L was deficit of the highly acidic domain of the tail region (∼77% of the entire tail region). Assembly of tail‐less neurofilament L was observed to be accelerated by both fluorometric and centrifugal measurements, compared with intact neurofilament L. The critical concentration of tail‐less neurofilament L, which constitutes the constant unassembled pool, was approximately 0.25‐times lower than that of neurofilament L. Under physiological conditions, tail‐less neurofilament L formed a ribbon‐like structure, wheres tail‐less neurofilament L could from 10‐nm filaments in an extremely low ionic‐strength buffer in the presence of 1 mM MgCl₂. An affinity‐purified antibody directed against the tail fragment also accelerated neurofilament L assembly. The tail fragment neither coassembled with neurofilament L nor affect neurofilament L assembly. The acidic domain of the tail region may regulate neurofilament assembly and may be involved in 10‐nm filament formation under physiological conditions.