Implication of the extracellular disulfide bond on myelin protein zero expression

Mutations in myelin protein zero (PO) are responsible for several periphera l neuropathies. We studied transport and membrane integration of the trunca ted PO mutants using transfected oligodendroglial cell line (Oln93). Starti ng with rat cDNA, we produced two PO deletions. The first, called PO-Tyr co ntains a 66 amino acid deletion in the extracellular domain and a tyrosine at the new position 32. In the second, called PO-Cys, the tyrosine 32 is re placed by a cysteine. This replacement restores a disulfide bond in the ext racellular domain. Our results show that PO proteins, truncated or not, wer e expressed in the plasma membrane of the transfected cells. Transcription rates of both mutants were normal. However, PO-Tyr was detected in only 3-5 % of the cells compared to the PO-Cys and the wild type. Thus, the disulfid e bond in the extracellular domain is important for stability and correct a ddressing of the PO protein.