Oligodendrocyte-specific protein (OSP) is a major component of CNS myelin

An oligodendrocyte-specific protein (OSP) cDNA was recently identified and found to be expressed primarily in oligodendrocytes and has a deduced amino acid sequence similar to that of peripheral myelin protein 22 (PMP-22). We raised antibodies against a synthetic peptide corresponding to OSP amino acid residues 179-194 which reacted with a 22 kd protein in mouse CNS. OSP immunoreactivity localized to spinal cord white matter tracts using immunohistochemistry in a similar distribution to that of MBP. OSP localized to CNS myelin biochemically with more than a 30-fold enrichment measured in purified myelin. We further purified the proteolipid fraction of myelin and determined that OSP contributes approximately 7% of total myelin protein making it the third most abundant protein in CNS myelin. No binding was found to several agglutinins or a HNK1-specific antibody suggesting that OSP is not a glycoprotein.