Journal
JOURNAL OF CELL SCIENCE
Volume 118, Issue 7, Pages 1363-1372Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jcs.01710
Keywords
sorting; glycosylation; synaptotagmin; RBL-2H3
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We have examined the trafficking of synaptotagmin (Syt) I and II in the mast cell line rat basophilic leukemia (RBL2H3). We demonstrate that both Syt I and Syt II travel through the plasma membrane and require endocytosis to reach their final intracellular localization. However, N- or C-terminal tagging of Syt II, but not of Syt I, prevents its internalization, trapping the tagged protein at the plasma membrane. Furthermore, a chimeric protein comprising a tagged luminal domain of Syt II fused with the remaining domains of Syt I also localizes to the plasma membrane, whereas a chimera consisting of tagged luminal domain of Syt I fused with Syt II colocalizes with Syt I on secretory granules. We also show that endocytosis of both Syt I and Syt II is strictly dependent on O-glycosylation processing, whereby O-glycosylation mutants of either protein fail to internalize and remain at the plasma membrane. Our results indicate that the luminal domains of Syt I and Syt II govern their internalization capacity from the plasma membrane and identify O-glycosylation as playing a crucial role in Syt trafficking in non-neuronal secretory cells.
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