On the assembly mechanism of neurofilaments

1. Isolated individual components of the triplet of neurofilaments from bovine brain can reassemble to make filaments with a specific structure, contrary to the already reported result that NF-H and NF-M cannot make filaments alone but can only make filaments by co-polymerization with NF-L. 2. This result suggests an alternative mechanism of assembly of the neurofilaments in which individual components of the triplet make filaments first, and then these aggregate to form the intact neurofilaments. 3. The triplet components of neurofilaments are reduced to a monomeric form in 8 M urea and 1% beta-mercaptoethanol (beta-ME) solution. However, in the absence of beta-ME, a part of each component of the triplet was preserved as oligomeric forms. 4. Among them, a stable tetramer of NF-L was isolated by DE-52 column chromatography using 6 M urea solution in the absence of beta-ME. 5. This results supports the hypothesis that this tetramer can be considered as a protofilament of the neurofilament structure.