Tyrosine phosphorylation of PNS myelin P(0) occurs in the cytoplasmic domain and is maximal during early development.

Abstract

P(0), the major protein of PNS myelin, is considered to play a critical role in the compaction and stabilization of myelin lamellae. The protein undergoes extensive posttranslational modifications, including phosphorylation at multiple serine moieties in the cytoplasmic region. Recently, we demonstrated that P(0) is phosphorylated on one or more tyrosine residues in rat nerve homogenates after incubation. In this study, we show that P(0) phosphorylated on tyrosine is also present in the intact animal. The proportion of P(0) molecules phosphorylated on tyrosine is highest during the first postnatal week, a period that coincides with the most rapid period of myelin deposition in the PNS. A peptide that constitutes the cytoplasmic domain was isolated from purified P(0) and shown by immunochemical and chemical means to be phosphorylated on the tyrosine corresponding to Y(191) in the intact protein. No evidence was obtained supporting the possibility that P(0) is phosphorylated on other tyrosine residues. The sequence of amino acids surrounding Y(191) resemble known substrate phosphorylation sites for some nonreceptor cytoplasmic tyrosine kinases, as well as tyrosine-based recognition signals associated with clathrin vesicle-mediated cndocytosis.