Bovine Peripheral Nervous System Myelin P2 Protein: Chemical and Immunological Characterization of the Cyanogen Bromide Peptides

Cleavage of bovine P2 protein by cyanogen bromide (CNBr) produced peptide fractions CN1, CN2, and CN3 which were isolated by gel filtration chromatography. CN2 was found to contain two NH2-terminals (lysine and valine) and accounted for both of the cysteine residues of P2. When reduced carboxymethylated P2 (RCM-P2) was digested with CNBr, peptides CN1 and CN3 were obtained as were (1) a peptide with NH2-terminal lysine (Lys) that contained no homoserine and only one cysteine residue and (2) a peptide with NH2-terminal valine (Val) that was co-eluted with CN3. These data and the chemical characterization of all the CNBr peptides obtained from P2 and RCM-P2 suggest that isolated P2 protein has a structure composed of the CNBr peptides in the order CN3-CN1-CN2(Val)-CN2(Lys) with an intrachain disulfide bond between the cysteine residues located in the two constituent peptides of CN2, CN2(Lys) and CN2(Val). To locate the neuritogenic region(s) within the P2 protein structure, CN1, CN2, and CN3 were tested for the ability to induced experimental allergic neuritis (EAN) in Lewis rats. The disease-inducing sites of P2 protein were found only in CN1; neither CN2 nor CN3 produced disease. EAN induced by CN1 was comparable to that induced with P2 protein as determined by disease onset, clinical symptoms, and histologic lesions.