A dual tyrosine‐leucine motif mediates myelin protein P₀ targeting in MDCK cells

Abstract

Differential targeting of myelin proteins to multiple, biochemically and functionally distinct Schwann cell plasma membrane domains is essential for myelin formation. In this study, we investigated whether the myelin protein P0 contains targeting signals using Madin-Darby canine kidney (MDCK) cells. By confocal microscopy, P0 was localized to MDCK cell basolateral membranes. C-terminal deletion resulted in apical accumulation, and stepwise deletions defined a 15-mer region that was required for basolateral targeting. Alanine substitutions within this region identified the YAML sequence as a functional tyrosine-based targeting signal, with the ML sequence serving as a secondary leucine-based signal. Replacement of the P0 ectodomain with green fluorescent protein altered the distribution of constructs lacking the YAML signal. Coexpression of the myelin-associated glycoprotein did not alter P0 distribution in MDCK cells. The results indicate that P0 contains a hierarchy of targeting signals, which may contribute to P0 localization in myelinating Schwann cells and the pathogenesis in human disease.

Neuropathy-related mutations alter the membrane binding properties of the human myelin protein P0 cytoplasmic tail

“…While T216ER behaved very similarly to wt-P0ct, its role in CMT etiology could be of another origin than related to protein-membrane binding. A221T, on the other hand, resides in the YAML-motif, which directs the trafficking of P0 (Kidd et al 2006) and might compromise the function of P0 even without inducing changes in membrane binding, especially when combined with a second mutation in the extracellular domain, such as the deletion of Val42 (Planté-Bordeneuve et al 2001).…”

A nonsense mutation in Myelin Protein Zero causes congenital hypomyelination neuropathy through altered P0 membrane targeting and gain of abnormal function

“…As one of the known functions for P0 cytoplasmic domain, which is truncated in P0Q215X, is to target the protein to myelin (Kidd et al, 2006), we analysed in detail the membrane targeting of the protein, and found that Q215X was increasingly mis-directed to non-myelin plasma membranes.…”

“…P0Q215X lacks a YAML sequence in its C-terminal region, which has previously been implicated in myelin membrane targeting (Kidd et al, 2006). In order to address whether this determines the altered trafficking of P0Q215X, we used an in vitro assay where the YAML motif directs P0 trafficking to the basolateral surface of transfected and polarized MDCK cells (Kidd et al, 2006).…”

“…To date there are over 100 mutations in MPZ, known to cause peripheral neuropathies in patients and, although most of them are located in the extracellular domain of P0, few mutations in the short cytoplasmic domain were also reported (Warner et al, 1996;Baets et al, 2011). The intracellular tail of P0 has several putative functions, including compacting the cytoplasmic apposition in myelin (Martini et al, 1995), modulating adhesion by the P0 ectodomain (Xu et al, 2001;Wong et al, 1994 and and directing trafficking of P0 through the YAML motif (Kidd et al, 2006).…”

Sorting signals and regulation of cognate basolateral trafficking in myelin biogenesis

“…Moreover, both isoforms of MAG contain a sequence resembling a clathrin‐coated pit internalization signal, including a tyrosine, which is crucial for basolateral sorting (Matter and Mellman, 1994). Of further interest, in the myelin protein P 0 , a dual tyrosine‐leucine motif that mediates basolateral targeting in MDCK cells has been identified (Kidd et al, 2006). Finally, PLP contains a dileucine motif that localizes in the N‐terminal region immediately next to the palmitoylation sites, which were reported to be imperative for the proper transport of PLP to the myelin sheet (Pham‐Dinh et al, 1991; Schneider et al, 2005).…”