N-Linked Glycosylation of the p24 Family Protein p24δ5 Modulates Retrograde Golgi-to-ER Transport of K/HDEL Ligands in Arabidopsis.

The K/HDEL receptor ERD2 mediates the transport of soluble endoplasmic reticulum (ER)-resident proteins containing a C-terminal K/HDEL signal from the Golgi apparatus back to the ER via COPI (COat Protein I)-coated vesicles. Sorting of ERD2 within COPI vesicles is facilitated by p24 proteins. In Arabidopsis, p24δ5 has been shown to interact directly with ERD2 via its luminal GOLD (GOLgi Dynamics) domain and with COPI proteins via its cytoplasmic C-terminal tail at the acidic pH of the Golgi apparatus. Several members of the p24 family in mammals and yeast have been shown to be glycosylated, but whether Arabidopsis p24 proteins are glycosylated and the role of the sugar moiety in p24 function remain unclear. Here, we show that Arabidopsis p24δ5 protein is N-glycosylated in its GOLD domain. Furthermore, we demonstrate that this post-translational modification is important for its coupled transport with p24β2 at the ER-Golgi interface, for its interaction with the K/HDEL receptor ERD2, and for retrograde transport of ERD2 and K/HDEL ligands from the Golgi apparatus back to the ER.