Determinant of Myelin Basic

Myelin encephalitogenic or basic protein (BP) 1 accounts for 30% of the protein in central nervous system (CNS) myelin (1), where BP is postulated to serve a structural role. BP is unique to myelin, and a similar, if not identical, protein designated P1 (2) is present in peripheral nervous system (PNS) myelin (2-4). BP has a monomeric mol wt of 18,500 daltons and is comprised of 169 amino acids. The amino acid sequence has been determined for BP from human (5) and bovine (6) sources and the small BP of the rat (7). In addition to its extensively investigated property of inducing experimental allergic encephalomyelitis (EAE), BP may also sensitize lymphocytes and stimulate antibody formation. Lymphocyte sensitization and antibody formation to BP may occur independent of each other and of EAE (8-10). The molecular portion of BP responsible for inducing EAE is different for the guinea pig (11), rabbit (12, 13), and Lewis rat (14), and there appear to be differences in the antigenic determinants recognized by guinea pig (15) and rabbit (16) antibodies to BP. The conformation of BP is likely to be important in the stability of the myelin sheath and in influencing the immune response after injection. The conformation of BP in the CNS myelin membrane and in solution is unresolved (17). While some studies have indicated that BP has only random-coil structure (1823) other investigations have provided findings suggestive of a prolate ellipsoid conformation (24, 25). In a previous study of the antigenic determinants of bovine BP (16), we reported that peptide 43-88 had limited participation as an antigenic determinant recognized by complement (C)-fixing antibodies in two rabbit antisera to BP. This finding prompted speculation that peptide 43-88