title: Secretory cargo sorting by Ca2+-dependent Cab45 oligomerization at the trans-Golgi network.
abstract: Sorting and export of transmembrane cargoes and lysosomal hydrolases at the trans-Golgi network (TGN) are well understood. However, elucidation of the mechanism by which secretory cargoes are segregated for their release into the extracellular space remains a challenge. We have previously demonstrated that, in a reaction that requires Ca(2+), the soluble TGN-resident protein Cab45 is necessary for the sorting of secretory cargoes at the TGN. Here, we report that Cab45 reversibly assembles into oligomers in the presence of Ca(2+) These Cab45 oligomers specifically bind secretory proteins, such as COMP and LyzC, in a Ca(2+)-dependent manner in vitro. In intact cells, mutation of the Ca(2+)-binding sites in Cab45 impairs oligomerization, as well as COMP and LyzC sorting. Superresolution microscopy revealed that Cab45 colocalizes with secretory proteins and the TGN Ca(2+) pump (SPCA1) in specific TGN microdomains. These findings reveal that Ca(2+)-dependent changes in Cab45 mediate sorting of specific cargo molecules at the TGN.
authors.affiliation: Physical Chemistry, Department of Chemistry Center for Nanoscience, Nanosystems Initiative Munich and Center for Integrated Protein Science Munich, Ludwig Maximilians University Munich, 81377 Munich, Germany vonblume@biochem.mpg.de alvaro.crevenna@cup.uni-muenchen.de.
authors.forename: Alvaro H
authors.initials: AH
authors.lastname: Crevenna
authors.affiliation: Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Blank
authors.affiliation: Department of Biology II, Ludwig Maximilian University Munich, 82152 Martinsried, Germany Center for Integrated Protein Science, Ludwig Maximilians University Munich, 82152 Martinsried, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Maiser
authors.affiliation: Physical Chemistry, Department of Chemistry Center for Nanoscience, Nanosystems Initiative Munich and Center for Integrated Protein Science Munich, Ludwig Maximilians University Munich, 81377 Munich, Germany.
authors.forename: Derya
authors.initials: D
authors.lastname: Emin
authors.affiliation: Physical Chemistry, Department of Chemistry Center for Nanoscience, Nanosystems Initiative Munich and Center for Integrated Protein Science Munich, Ludwig Maximilians University Munich, 81377 Munich, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Prescher
authors.affiliation: Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Gisela
authors.initials: G
authors.lastname: Beck
authors.affiliation: Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Kienzle
authors.affiliation: Physical Chemistry, Department of Chemistry Center for Nanoscience, Nanosystems Initiative Munich and Center for Integrated Protein Science Munich, Ludwig Maximilians University Munich, 81377 Munich, Germany.
authors.forename: Kira
authors.initials: K
authors.lastname: Bartnik
authors.affiliation: Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Bianca
authors.initials: B
authors.lastname: Habermann
authors.affiliation: Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Mehrshad
authors.initials: M
authors.lastname: Pakdel
authors.affiliation: Department of Biology II, Ludwig Maximilian University Munich, 82152 Martinsried, Germany Center for Integrated Protein Science, Ludwig Maximilians University Munich, 82152 Martinsried, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Leonhardt
authors.affiliation: Physical Chemistry, Department of Chemistry Center for Nanoscience, Nanosystems Initiative Munich and Center for Integrated Protein Science Munich, Ludwig Maximilians University Munich, 81377 Munich, Germany.
authors.forename: Don C
authors.initials: DC
authors.lastname: Lamb
authors.affiliation: Max Planck Institute of Biochemistry, 82152 Martinsried, Germany vonblume@biochem.mpg.de alvaro.crevenna@cup.uni-muenchen.de.
authors.forename: Julia
authors.initials: J
authors.lastname: von Blume
mesh_terms: D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D006023:Glycoproteins / Q000378:metabolism / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D008958:Models, Molecular; D011506:Proteins / Q000378:metabolism; D055571:Secretory Pathway; D021601:trans-Golgi Network / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D006023:Glycoproteins; D011506:Proteins; C099100:SDF4 protein, human; D002118:Calcium