The proposed amino acid sequence of the P1 protein of rabbit sciatic nerve myelin

Abstract

A basic protein (P1 protein) exists in rabbit sciatic nerve myelin that appears to have the same amino acid sequence as the rabbit A1 protein, a basic protein of central nervous system myelin. The amino acid sequences proposed for the two rabbit proteins are compared with the bovine and human A1 proteins; differences (substitutions, deletions, additions) in approximately 15 residues are observed. The amino acid sequence of each rabbit protein (168 amino acids, M r 18,100) was assessed by amino acid analysis of each tryptic peptide obtained by elution of the ninhydrin-positive spots from the tryptic peptide map. Peptides were judged to have the same or similar sequence if they migrated to the same position on the peptide map as the analogous peptide from the bovine A1 protein, and if they had the same or similar composition as the bovine peptides. Several characteristic features of the bovine A1 protein are preserved in the two rabbit proteins: the region surrounding the molecules single tryptophan residue; the rare triproline sequence; the methylated arginine derivatives localized exclusively at position 107 of the bovine A1 protein; and the reactive threonine residue which serves as an acceptor for glycosylation by the polypeptide: N-acetylgalactosaminyl transferase.