Differences between the two myelin basic proteins of the rat central nervous system: A deletion in the smaller protein

Abstract

Myelin of the rat central nervous system contains two highly basic proteins which differ in molecular size, amino acid composition, and encephalitogenic activity. The larger rat protein is very similar to the myelin basic proteins of beef and human in total polypeptide chain length, amino acid composition, encephalitogenic activity, and length of the polypeptide chain between the two methionyl residues. The length of polypeptide chain between the two methionyl residues of the smaller rat protein is considerably less than the corresponding segment of the larger. Both proteins contain 1 mole of tryptophan per mole of protein. The difference in amino acid compositions of the two rat proteins, together with the amino acid compositions of the tryptic peptides present in the larger rat protein but missing in the smaller indicate a deletion in the smaller protein corresponding to bovine and human residues 117–156 or 118–157. The new tryptophan-containing peptide created by the deletion has the composition (Phe, Ser, Trp, Gly 2) Arg. This deletion removes a major part of the peptide reported to be encephalitogenic in the guinea pig. Loss of the Gln-Lys portion of this latter peptide explains our observation that the smaller protein is much less encephalitogenic in the guinea pig than the larger.