Understanding Periperal Membrane Protein Interactions | BPS Thematic Meeting

Understanding Peripheral Membrane Protein Interactions: Structure, Dynamics, Function and Therapy

Thursday Speaker Abstracts

BRIDGING PROTEIN TTR-53 MEDIATES PHOSPHATIDYLINOSITOL PHOSPHATE SIGNALING FOR CELL CORPSE CLEARANCE Dylan Suriadinata 1 ; Chinmay Phadke 1 ; Riley Harrison 2 ; Julia Frondoni 2 ; Gabriela S Paredes Davalillo 2 ; Ann W Wehman 1,2 ; 1 Texas A&M University, Biochemistry & Biophysics, College Station, TX, USA 2 University of Denver, Biological Sciences, Denver, CO, USA Secreted peripheral membrane proteins recognize phagocytic cargoes by their exposure of cytofacial lipids. Tissue homeostasis and immune responses rely on timely clearance of dying cells and cell debris. The secreted transthyretin-like protein TTR-52 recognizes apoptotic cells for receptor-mediated phagocytosis by bridging phosphatidylserine (PtdSer) and engulfment receptor CED-1 but is not required for the engulfment of all dying cells in Caenorhabditis elegans. We discovered that a closely related secreted protein, TTR-53, also promotes phagocytosis. We tagged endogenous TTR-53 with fluorescent proteins and observed localization to cargo surfaces prior to phagocytosis, including dying polar bodies and midbody remnants. Knocking down or deleting ttr-53 disrupted polar body phagocytosis, but midbody remnant clearance was not delayed in ttr-53 mutants. This indicates that cells can use both TTR 53-dependent and TTR-53-independent pathways for distinct cargoes. To establish whether TTR-53 binds PtdSer similar to TTR-52, we induced PtdSer exposure by disrupting flippase TAT-1. TTR-53 localization was unchanged after tat-1 RNAi treatment or tat-1 deletion, revealing that TTR-53 is unlikely to bind PtdSer. We purified recombinant TTR-53 and discovered that it binds to phosphatidylinositol 3,4,5-trisphosphate (PIP3) and phosphatidylinositol bisphosphate (PIP2) lipids on dot blots in a calcium-dependent manner. Therefore, we propose that TTR-53 acts as a bridging molecule between PIPs and engulfment receptors to promote phagocytosis of dying cells. To determine whether PtdSer and PIP exposure form redundant phagocytic signaling pathways, we asked whether preventing PtdSer synthesis could enhance phagocytic defects when TTR-53 is absent. We found that knocking down the PtdSer synthase pssy-1 enhanced internalization defects in ttr-53 mutants, but pssy-1 knockdown did not disrupt polar body internalization when TTR-53 was present. These data indicate animal cells use interchangeable and conserved lipid-based signaling pathways to recognize dying cells, emphasizing the importance of clearing cell corpses for normal physiology.

CONFORMATIONAL ENSEMBLES AND CONDUCTIVITY MODELING IN TETRAMERIC ION CHANNEL RECEPTORS Maria Kurnikova 1 ; 1 Carnegie Mellon University, Pittsburgh, Pennsylvania, USA No Abstract

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