Interdomain Interactions Regulate the Localization of a Lipid Transfer Protein at ER-PM Contact Sites

ABSTRACT During phospholipase C-β (PLC-β) signalling in Drosophila photoreceptors, the phosphatidylinositol transfer protein (PITP) RDGB, is required for lipid transfer at endoplasmic reticulum (ER)–plasma membrane (PM) contact sites (MCS). Depletion of RDGB or its mis-localization away from the ER–PM MCS results in multiple defects in photoreceptor function. Previously, the interaction between the FFAT motif of RDGB and the integral ER protein dVAP-A was shown to be essential for accurate localization to ER–PM MCS. Here, we report that the FFAT/dVAP-A interaction alone is insufficient to localize RDGB accurately; this also requires the function of the C-terminal domains, DDHD and LNS2. Mutations in each of these domains results in mis-localization of RDGB leading to loss of function. While the LNS2 domain is necessary, it is not sufficient for the correct localization of RDGB, which also requires the C-terminal DDHD domain. The function of the DDHD domain is mediated through an intramolecular interaction with the LNS2 domain. Thus, interactions between the additional domains in a multi-domain PITP together lead to accurate localization at the MCS and signalling function. This article has an associated First Person interview with the first author of the paper. Summary: This study demonstrates interdomain interactions within a phosphatidylinositol transfer protein that regulate its localization and function at an ER-PM membrane contact site.