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

Abstract

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 NH-₂-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 induce 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.