VAP-A intrinsically disordered regions enable versatile tethering at membrane contact sites

VAP-A is a receptor at the surface of the endoplasmic reticulum (ER) for hundreds of proteins containing a FFAT motif and having a wide range of structures and functions. VAP-A is also required for creating multiple membrane contact sites (MCSs) between the ER and other compartments, which notably enable non-vesicular lipid exchanges between membranes. For example, the lipid-transfer protein (LTP) OSBP interacts with VAP at ER/Golgi MCS to transport cholesterol through coupled counter-exchange and hydrolysis of PI4P. It is well known that VAP-A partners contain a FFAT motif specifically recognized by the Major-Sperm-Protein (MSP) domain of VAP, however, how this receptor adapts to its different targets in MCSs that are so different in geometry and lifetime is not understood.In this study, we used a multidisciplinary approach to demonstrate that VAP-A contains two intrinsically disordered linkers that provide it with a high degree of flexibility to enable functional organization of different MCSs. A VAP-A mutant without flexible linkers is restricted in its subcellular localization, and does not support lipid transport by OSBP and CERT at ER/Golgi MCS. However, this mutant is present at ER/mitochondria MCS by interacting with VPS13A and PTPIP51, and thus facilitates lipid transport contributing to cardiolipin metabolism and mitochondrial fusion.In conclusion, this work indicates that VAP-A conformational flexibility mediated by its intrinsically disordered regions is key to ensure membrane tethering especially at short-lived MCSs; it also demonstrates the implication of VAP-A in mitochondrial fusion.