English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Parafusin, a cytosolic phosphoglycoprotein of M(r) 63,000, is dephosphorylated and rephosphorylated rapidly in a Ca(2+)-dependent manner upon stimulation of exocytosis in vivo in wild-type (wt) Paramecium. In contrast, the temperature-sensitive exocytosis mutant nd9, grown at the nonpermissive temperature (27 degrees C), does not exocytose or dephosphorylate parafusin upon stimulation in the presence of Ca2+; grown at the permissive temperature (18 degrees C), nd9 cells show a wt phenotype. Parafusin contains two types of phosphorylation sites: one where glucose 1-phosphate is added by an alpha-glucose-1-phosphate phosphotransferase and removed by a phosphodiesterase and one where phosphate from ATP is added directly to a serine residue by a protein kinase and removed by a phosphatase. We show here that, in cell fractions from wt Paramecium, both reactions can be carried out in vitro by using uridine(5'-[beta-[35S]thio])diphospho(1)-glucose (UDP[beta 35S]-Glc) and [gamma-32P]ATP, respectively. The characteristics of these pathways are different. Specifically, in the presence of Ca2+, the amount of UDP[beta 35S]-Glc label in parafusin is reduced. In contrast, identical labeling experiments with [gamma-32P]ATP show that Ca2+ enhances labeling of parafusin. Mg2+ had no appreciable effect on either labeling. Removal of the UDP[beta 35S]-Glc label on parafusin in the presence of Ca2+ correlates with the in vivo dephosphorylation seen upon exocytosis. Incubations with UDP[beta 35S]-Glc were then performed with homogenates and nd9 cell fractions grown at 27 degrees C under the ionic conditions used for wt cells. These labelings were not affected by Ca2+, in contrast to results from wt cells but in accord with those obtained earlier with nd9-27 mutant cells in vivo. Factors responsible for both dephosphorylation and Ca2+ sensitivity were found in the high-speed pellet (P2) in wt cells, suggesting that the putative phosphodiesterase is in this fraction and that the defect in the mutant nd9-27 residues in the Ca2+ activation of the phosphodiesterase. We conclude that the in vivo dephosphorylation of parafusin that occurs upon exocytosis is a dephosphoglucosylation due to removal of the alpha-glucose 1-phosphate and more generally that carbohydrates on cytoplasmic glycoproteins may be cyclically added and/or removed in response to extracellular stimuli.

proceedings of the national academy of sciences of the united states of america

Carbohydrate cycling in signal transduction: parafusin, a phosphoglycoprotein and possible Ca(2+)-dependent transducer molecule in exocytosis in Paramecium.