The transmission of electrical impulses along the axons of the nervous system is only possible because each axon is surrounded by an insulating coat of myelin made by the oligodendrocytes and Schwann cells. How myelin-specific proteins are targeted to this specialized multilamellar membrane is poorly understood. Now, on , Mikael Simons and colleagues report that palmitoylation is an important sorting determinant for protein transport to the myelin membrane. Using a primary oligodendrocyte culture system in which there is excessive deposition of myelin-like membranes (MLMs), the authors show that palmitoylation-deficient mutants of a major myelin protein, proteolipid protein (PLP/DM20), are less efficiently targeted to MLMs than wild-type PLP/DM20. The N-terminal 13 residues of PLP/DM20, which are palmitoylated at three sites, are sufficient to target a fluorescent fusion protein to the MLMs, as are palmitoylation signals from Ha-Ras and neuromodulin. However, note the authors, palmitoylation is probably only one of a hierarchy of sorting determinants that together generate the full complexity of the myelin membrane.
