Comparative studies of the neurofilament triplet protein peptide mapping by chemical cleavage

Peptide mapping of the three neurofilament protein subunits with apparent mol. weights of 210 kDa, 160 kDa and 70 kDa was performed with two different reagents: CNBr, BNPS-Skatole leading to the cleavage of methionyl and tryptophanyl bonds respectively. With BrCN we obtained two large fragments resistant to the cleavage, with mol. wts of 85 kDa for the 160 kDa and 135 kDa for the 210 kDa neurofilament proteins respectively. These fragments were located on the C-terminal part of the proteins (the tails) and correspond to specific regions responsible for their physiological identity. On the other hand, the cleavage with BNPS-Skatole at the tryptophanyl bonds gave similar patterns. The 210 kDa and 160 kDa neurofilament proteins gave a doublet of high mol. wt resistant to the cleavage, corresponding very likely to the C-terminal part and 4 fragments of mol. wt between 30 and 40 kDa corresponding to the N-terminal part. The neurofilament triplet share a common 30.5 kDa fragment located on the N-terminal part. From these peptide mapping studies, we conclude that the two neurofilament subunit proteins with mol. wts of 160 kDa and 210 kDa are different but related structures and that the CNBr characterized cleavage fragments of mol. wt 85,000 and 135 kDa are suitable polypeptides for sequence and immunological studies of the C-terminal part of these proteins.