PLAT Domain Protein 1 (PLAT1/PLAFP) Binds to the Arabidopsis thaliana Plasma Membrane and Inserts a Lipid

Harvest yields depend on the plant's ability to fix carbon and deal with changing environmental conditions. Especially during seasonal and diurnal cycles, the plant must constantly adjust its metabolism according to available resources or external stressors. The metabolic changes that a plant undergoes in response to stress are well understood, but the long-distance signaling mechanisms that facilitate communication throughout the plant are less studied. The phloem is considered the predominant conduit for the bidirectional transport of these signals through metabolites, nucleic acids, proteins, and lipids. Lipid trafficking through the phloem in particular attracted our attention due to its reliance on soluble lipid-binding proteins (LBP) that generate and solubilize otherwise membrane-associated lipids. The Phloem Lipid-Associated Family Protein (PLAFP) from Arabidopsis thaliana is generated in response to abiotic stress as is its lipid-ligand phosphatidic acid (PA). PLAFP is proposed to transport PA through the phloem in response to drought stress. To understand the interactions between PLAFP and PA, almost 100 independent systems comprised of the protein and one PA, or a plasma membrane containing varying amounts of PA, were simulated. In the simulations, PLAFP does bind to the plasma membrane independent of the PA concentration, and it adopts a binding pose, where W41 and R82 penetrate the membrane surface and anchor PLAFP. This triggers a separation of the two loop regions containing W41 and R82. Subsequently, PA does insert into PLAFP's beta-sandwich and multiple amino acids besides W41 and R82 are identified that drive the insertion. Fine-tuning the protein-membrane and protein-PA interface by mutating a selection of these amino acids could allow modulating the signaling sensitivity to the climate the plant is supposed to grow in.