Control of interorganelle membrane contact formation – CO-CON

Proteomics
Surface plasma resonance
Structural determination of protein complexes involved in the association between two organelles
Writing prediction algorithm for a new consensus motif
In vitro reconstruction of membrane contact sites
In vitro determination of cholesterol transport kinetics in real time
In vivo and in situ analysis of cholesterol fluxes in cell

Inside cells, organelles are connected together in a network built by inter-organelle membrane contact sites. In this network, the endoplasmic reticulum (ER) plays a central role making numerous contacts with all the other cellular organelles. To achieve this, the ER is equipped at its surface with receptors capturing proteins attached to other organelles via protein-protein interactions. However, how the ER manages to make reversible associations with other organelles was not understood. Our collaborative project showed for the first time that phosphorylation acts as a general switch for inter-organelle contacts. This mechanism explains the formation of reversible membrane contact sites between the ER and the other cellular organelles.

Our study has highlighted a novel mechanism of reversible formation of inter-organelle contact sites. The involved proteins identified in our study are embedded in the membranes of the partner organelles, which means that the formation and dissociation of distinct inter-organelle contacts is under the direct control of cell signaling. The next logical and exciting step in this work is the search for the kinases and phosphatases responsible for this mechanism.

Di Mattia T, Martinet A, Ikhlef S, Mc Ewen AG, Nominé Y, Wendling C, Poussin-Courtmontagne P, Eberling P, Ruffenach F, Cavarelli J, Slee J, Levine TP, Drin G, Tomasetto C and Alpy F FFAT motif phosphorylation controls formation and lipid transfer function of inter-organelle contacts. EMBO J (2020)39:e104369https://doi.org/10.15252/embj.2019104369

Eukaryotic cells are compartmentalized in distinct organelles, each of them hosting specialized functions. They are not isolated from each other but physically and transiently connected, through the formation of membrane contact sites (MCS). The endoplasmic reticulum (ER) is the most connected organelle, owing to the presence along its surface of receptors of the VAMP-associated protein (VAP) family. These receptors VAP-A, VAP-B and the recently identified MOSPD2, by recognizing a short linear peptide motif called FFAT, are critical for the formation and the function of ER-organelle contact sites. Yet our knowledge on MCSs reaches its limit. We do not know how these contacts are regulated. The aim of this project is to unveil a new mechanism regulating the formation of MCS and establish the repertoire of constitutive and regulatable complexes bridging the ER with other organelles.