| Autor: |
Ramazanov BR; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510., Parchure A; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510., Di Martino R; Institute of Biochemistry and Cell Biology, National Research Council, Naples 80131, Italy., Kumar A; Yale Cardiovascular Research Center, Yale University School of Medicine, New Haven, CT 06510., Chung M; Yale Cardiovascular Research Center, Yale University School of Medicine, New Haven, CT 06510., Kim Y; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510., Griesbeck O; Max Planck Institute of Neurobiology, Martinsried 82152, Germany., Schwartz MA; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510.; Yale Cardiovascular Research Center, Yale University School of Medicine, New Haven, CT 06510.; Department of Biomedical Engineering, Yale University, New Haven, CT 06511., Luini A; Institute of Biochemistry and Cell Biology, National Research Council, Naples 80131, Italy., von Blume J; Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510. |
| Abstrakt: |
Ca 2+ influx into the trans -Golgi Network (TGN) promotes secretory cargo sorting by the Ca 2+ -ATPase SPCA1 and the luminal Ca 2+ binding protein Cab45. Cab45 oligomerizes upon local Ca 2+ influx, and Cab45 oligomers sequester and separate soluble secretory cargo from the bulk flow of proteins in the TGN. However, how this Ca 2+ flux into the lumen of the TGN is achieved remains mysterious, as the cytosol has a nanomolar steady-state Ca 2+ concentration. The TGN forms membrane contact sites (MCS) with the Endoplasmic Reticulum (ER), allowing protein-mediated exchange of molecular species such as lipids. Here, we show that the TGN export of secretory proteins requires the integrity of ER-TGN MCS and inositol 3 phosphate receptor (IP3R)-dependent Ca 2+ fluxes in the MCS, suggesting Ca 2+ transfer between these organelles. Using an MCS-targeted Ca 2+ FRET sensor module, we measure the Ca 2+ flow in these sites in real time. These data show that ER-TGN MCS facilitates the Ca 2+ transfer required for Ca 2+ -dependent cargo sorting and export from the TGN, thus solving a fundamental question in cell biology. |
