Self-assembly in vitro of the 68,000 molecular weight component of the mammalian neurofilament triplet proteins into intermediate-sized filaments

The mammalian neurofilament triplet proteins (210, 160 and 68 × 10³M_r proteins) are resolved by anion exchange chromatography in the presence of urea. Upon dialysis against physiological buffers at 37 °C only the 68 × 10³M_r protein shows self-assembly into morphologically normal intermediate-sized filaments. Addition of 210 × 10³M_r protein to 68 × 10₃M_r protein leads to shorter filaments, which upon embedding reveal a rough surface and whisker-like protrusions that are not present on the smooth surface of filaments assembled from 68 × 10₃M_r protein alone. Certain emerging principles of neurofilament structure are discussed, emphasizing a possible relation between neurofilaments and other intermediate-sized filaments.