Proteolysis of the neurofilament 68 kDa protein explains several previously described brain proteins of unique composition and high acidity

Neurofilaments follow the structural principles of non-neuronal intermediate filaments but contain additional sequences which are carboxyterminally located and increase in length between triplet proteins (68 kDa, 160 kDa and 200 kDa). The tailpiece domain has been sequenced in the case of the porcine 68 kDa protein. It has a unique amino acid composition. Within 106 residues there are only 12 different amino acid types, and glutamic acid accounts for 46% of the sequence. Examination of the literature on highly acidic brain proteins leads us to the proposal that microglutamic acid-rich protein, Glu-50, macroglutamic protein, as well as some unusual components of the S100 class, are most likely proteolytic degradation products of the neurofilament 68 kDa protein.