Immunochemical differentiation of highly conserved forms of myelin proteolipid

1. Myelin proteolipid proteins (PLPs) from five animal species were compared immunochemically. In direct electroblot, ELISA or immunodot analyses, anti-bovine PLP antiserum reacted similarly with bovine, guinea-pig, human, mouse and rat myelin PLP. In contrast, antiserum to bovine BPS4, a fragment obtained by chemical cleavage of bovine PLP, reacted strongly only with the bovine protein. 2. In comparable competitive assays in which antisera were preincubated with PLP from different species prior to reaction with bovine PLP, only preincubation with bovine PLP removed the antibody effectively; PLP from other species competed poorly. 3. The deduced primary structure of human, mouse and rat PLP from their cDNA indicates sequence identity. However, these sequences differ from bovine PLP at four residues, two of them within the BPS4 region. The results suggest that, while anti-PLP antiserum fails to differentiate heterologous from homologous antigen, anti-fragment antiserum can be useful for determining structural relatedness of proteins, especially when used in competitive assays.