Sulfate metabolism of rat P0 glycoprotein: some observations

It has been known for some time that P0, the major intrinsic protein in PNS myelin, contains sulfate. The position of sulfate has been described for beef PNS myelin, but rat PNS myelin differs somewhat from that of the beef, therefore an investigation of the location of sulfate in rat P0 was undertaken. Weanling rat nerves were incubated with [3H] amino acid mixture and [35S]O4, and purified myelin was prepared, and the proteins separated on polyacrylamide gels. The bulk of the [35S]O4 was incorporated into P0, but smaller peaks of sulfate label were found in the higher molecular weight proteins. With tunicamycin in the incubation mixture, sulfate incorporation was inhibited. Incubation of the labeled myelin mixture with endo F or glycanase resulted in total loss of sulfate label on P0, therefore all of the [35S]O4 was incorporated into the oligosaccharide chain, with none on the polypeptide. Castanospermine and deoxymannojirimycin inhibited [35S]O4 incorporation into P0, but no inhibition was exerted by swainsonine. These results indicate that sulfate resides in the core of the oligosaccharide chain, with none in the terminal region. Such a structure would correlate with the lack of an HNK-1 epitope, absent in the rat, but found in P0 of many species.