Abstract
Most proteins in the secretory pathway are glycosylated. However, the role of glycans in membrane trafficking is still unclear. Here, we discovered that transmembrane secretory cargos, such as interleukin 2 receptor α subunit or Tac, transferrin receptor, and cluster of differentiation 8a, unexpectedly displayed substantial Golgi localization when their O-glycosylation was compromised. By quantitatively measuring their Golgi residence times, we found that the observed Golgi localization of O-glycan–deficient cargos is due to their slow Golgi export. Using a superresolution microscopy method that we previously developed, we revealed that O-glycan–deficient Tac chimeras localize at the interior of the trans-Golgi cisternae. O-Glycans were observed to be both necessary and sufficient for the efficient Golgi export of Tac chimeras. By sequentially introducing O-glycosylation sites to ST6GAL1, we demonstrated that O-glycan's effect on Golgi export is probably additive. Finally, the finding that N-glycosylated GFP substantially reduces the Golgi residence time of a Tac chimera suggests that N-glycans might have a similar effect. Therefore, both O- and N-glycans might function as a generic Golgi export signal at the trans-Golgi to promote the constitutive exocytic trafficking.
Highlights
Most proteins in the secretory pathway are glycosylated
During our study of secretory cargos, we focused on the cell surface receptor, interleukin 2 (IL2) receptor a subunit, or Tac
By quantitatively measuring the Golgi residence times of transmembrane secretory reporters, we further pinpointed that both O- and N-glycans can function as a signal for the efficient Golgi export
Summary
Most proteins in the secretory pathway are glycosylated. the role of glycans in membrane trafficking is still unclear. The finding that N-glycosylated GFP substantially reduces the Golgi residence time of a Tac chimera suggests that N-glycans might have a similar effect.
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