Abstract
ABSTRACTDuring 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.
Highlights
The close approximation of intracellular membranes without fusion between them is emerging as a theme in cell biology (Gatta and Levine, 2017)
The protein with a single phosphatidylinositol transfer domain (PITPd) and FFAT motif of Retinal Degeneration B (RDGB) is insufficient for RDGB function at endoplasmic reticulum (ER)-plasma membrane (PM) contact sites When the PITPd of RDGB is expressed in photoreceptors, it is distributed diffusely in the cell body
We generated a truncated construct of RDGB removing everything C-terminal to the FFAT motif named as RDGBPITPd-FFAT (Fig. 1B- RDGBPITPd-FFAT), and expressed it in rdgB9 photoreceptors (Fig. S1A)
Summary
The close approximation of intracellular membranes without fusion between them is emerging as a theme in cell biology (Gatta and Levine, 2017). Such apposition of membranes, referred to as membrane contact sites (MCS) can occur between multiple cellular organelles; most frequently, the endoplasmic reticulum (ER) which is the largest organelle, makes MCS with other cellular organelles including the plasma membrane (PM) (Cohen et al, 2018). The transfer of lipids between organelle membranes is a key function proposed for MCS. In the case of ER-PM contact sites, multiple lipids are thought to be transferred including. Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bengaluru 560065, India.
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