FFAT motif phosphorylation controls formation and lipid transfer function of inter‐organelle contacts

• Published in: The EMBO journal Vol. 39; no. 23; pp. e104369 - n/a
• Main Authors: Di Mattia, Thomas, Martinet, Arthur, Ikhlef, Souade, McEwen, Alastair G, Nominé, Yves, Wendling, Corinne, Poussin‐Courmontagne, Pierre, Voilquin, Laetitia, Eberling, Pascal, Ruffenach, Frank, Cavarelli, Jean, Slee, John, Levine, Timothy P, Drin, Guillaume, Tomasetto, Catherine, Alpy, Fabien
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.12.2020; Blackwell Publishing Ltd; EMBO Press; John Wiley and Sons Inc
• Subjects: Algorithms; Amino Acid Motifs; Apposition; Binding Sites; Cellular Biology; cholesterol; Domains; EMBO20; EMBO57; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Endosomes; Endosomes - metabolism; Humans; inter‐organelle contact; Life Sciences; Lipid Metabolism; lipid transfer protein; Lipids; Membrane Proteins - chemistry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Membranes; Models, Molecular; Organelles; Peptides; Phosphorylation; Protein Binding; Proteins; Proteomes; Receptors; Receptors, Chemokine - chemistry; Receptors, Chemokine - genetics; Receptors, Chemokine - metabolism; regulation; Residues; Serine; small linear motif; Steroidogenic acute regulatory protein; Sterols; Subcellular Processes; Tethering; Threonine; Transfer functions; Vesicular Transport Proteins - chemistry; Vesicular Transport Proteins - genetics; Vesicular Transport Proteins - metabolism; inter‐organelle contact; cholesterol; regulation; small linear motif; lipid transfer protein; inter-organelle contact
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.2019104369

Organelles are physically connected by membrane contact sites. The endoplasmic reticulum possesses three major receptors, VAP‐A, VAP‐B, and MOSPD2, which interact with proteins at the surface of other organelles to build contacts. VAP‐A, VAP‐B, and MOSPD2 contain an MSP domain, which binds a motif named FFAT (two phenylalanines in an acidic tract). In this study, we identified a non‐conventional FFAT motif where a conserved acidic residue is replaced by a serine/threonine. We show that phosphorylation of this serine/threonine is critical for non‐conventional FFAT motifs (named Phospho‐FFAT) to be recognized by the MSP domain. Moreover, structural analyses of the MSP domain alone or in complex with conventional and Phospho‐FFAT peptides revealed new mechanisms of interaction. Based on these new insights, we produced a novel prediction algorithm, which expands the repertoire of candidate proteins with a Phospho‐FFAT that are able to form membrane contact sites. Using a prototypical tethering complex made by STARD3 and VAP, we showed that phosphorylation is instrumental for the formation of ER‐endosome contacts, and their sterol transfer function. This study reveals that phosphorylation acts as a general switch for inter‐organelle contacts. Synopsis Membrane contact sites (MCS) are subcellular domains formed by close apposition between the membranes of two organelles, which regulate lipid transport and organelle dynamics. Here, phosphorylation of a non‐conventional FFAT motif on Endoplasmic Reticulum (ER) receptor partner proteins is shown to mediate MCS formation and lipid transport. The ER receptors VAP‐A, VAP‐B and MOSPD2 bind a non‐conventional FFAT motif via their MSP domain. The alternative FFAT motif (Phospho‐FFAT) is characterized by a key phosphorylated serine/threonine residue. Structural analyses show that conventional FFATs and alternative phospho‐FFATs bind to VAP differently. An algorithm to predict Phospho‐FFAT motifs reveals that Phospho‐FFATs are as common as conventional FFATs in the human proteome. Phosphorylation acts as a switch that activates the ER–endosome MCS formation and sterol exchange. Graphical Abstract Phosphorylation of a non‐conventional FFAT motif promotes ER‐endosome membrane contact sites and sterol exchange.