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1. Open-channel structure of a pentameric ligand-gated ion channel reveals a mechanism of leaflet-specific phospholipid modulation

   https://doi.org/10.1038/s41467-022-34813-5  

   Petroff, II, John T.; Dietzen, Noah M.; Santiago-McRae, Ezry; Deng, Brett; Washington, Maya S.; Chen, Lawrence J.; Trent Moreland, K.; Deng, Zengqin; Rau, Michael; Fitzpatrick, James A. J.; et al (November 2022, Nature Communications)

   Abstract Pentameric ligand-gated ion channels (pLGICs) mediate synaptic transmission and are sensitive to their lipid environment. The mechanism of phospholipid modulation of any pLGIC is not well understood. We demonstrate that the model pLGIC, ELIC (Erwinialigand-gated ion channel), is positively modulated by the anionic phospholipid, phosphatidylglycerol, from the outer leaflet of the membrane. To explore the mechanism of phosphatidylglycerol modulation, we determine a structure of ELIC in an open-channel conformation. The structure shows a bound phospholipid in an outer leaflet site, and structural changes in the phospholipid binding site unique to the open-channel. In combination with streamlined alchemical free energy perturbation calculations and functional measurements in asymmetric liposomes, the data support a mechanism by which an anionic phospholipid stabilizes the activated, open-channel state of a pLGIC by specific, state-dependent binding to this site. 

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2. Arabidopsis   PROTODERMAL FACTOR2 binds lysophosphatidylcholines and transcriptionally regulates phospholipid metabolism

   https://doi.org/10.1111/nph.19917  

   Wojciechowska, Izabela; Mukherjee, Thiya; Knox‐Brown, Patrick; Hu, Xueyun; Khosla, Aashima; Subedi, Bibek; Ahmad, Bilal; Mathews, Graham L; Panagakis, Ashley A; Thompson, Kyle A; et al (July 2024, New Phytologist)

   Summary Plant homeodomain leucine zipper IV (HD‐Zip IV) transcription factors (TFs) contain an evolutionarily conserved steroidogenic acute regulatory protein (StAR)‐related lipid transfer (START) domain. While the START domain is required for TF activity, its presumed role as a lipid sensor is not clear.Here we used tandem affinity purification fromArabidopsiscell cultures to demonstrate that PROTODERMAL FACTOR2 (PDF2), a representative member that controls epidermal differentiation, recruits lysophosphatidylcholines (LysoPCs) in a START‐dependent manner. Microscale thermophoresis assays confirmed that a missense mutation in a predicted ligand contact site reduces lysophospholipid binding.We additionally found that PDF2 acts as a transcriptional regulator of phospholipid‐ and phosphate (Pi) starvation‐related genes and binds to a palindromic octamer with consensus to a Pi response element. Phospholipid homeostasis and elongation growth were altered inpdf2mutants according to Pi availability. Cycloheximide chase experiments revealed a role for START in maintaining protein levels, and Pi starvation resulted in enhanced protein destabilization, suggesting a mechanism by which lipid binding controls TF activity.We propose that the START domain serves as a molecular sensor for membrane phospholipid status in the epidermis. Our data provide insights toward understanding how the lipid metabolome integrates Pi availability with gene expression. 

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3. Biomimetic construction of phospholipid membranes by direct aminolysis ligations

   https://doi.org/10.1098/rsfs.2023.0019  

   Souto-Trinei, Federica A.; Brea, Roberto J.; Devaraj, Neal K. (October 2023, Interface Focus)

   Construction of artificial cells requires the development of straightforward methods for mimicking natural phospholipid membrane formation. Here we describe the use of direct aminolysis ligations to spontaneously generate biomimetic phospholipid membranes from water-soluble starting materials. Additionally, we explore the suitability of such biomimetic approaches for driving the in situ formation of native phospholipid membranes. Our studies suggest that non-enzymatic ligation reactions could have been important for the synthesis of phospholipid-like membranes during the origin of life, and might be harnessed as simplified methods to enable the generation of lipid compartments in artificial cells. 

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4. Electromechanics of lipid-modulated gating of potassium channels

   https://doi.org/10.1177/10812865211060071  

   Thomas, Nidhin; Mandadapu, Kranthi_K; Agrawal, Ashutosh (December 2021, Mathematics and Mechanics of Solids)

   Experimental studies reveal that the anionic lipid phosphatidic acid (POPA), non-phospholipid cholesterol, and cationic lipid DOTAP inhibit the gating of voltage-sensitive potassium (Kv) channels. Here, we develop a continuum electromechanical model to investigate the interaction of these lipids with the ion channel. Our model suggests that: (i) POPA lipids may restrict the vertical motion of the voltage-sensor domain through direct electrostatic interactions; (ii) cholesterol may oppose the radial motion of the pore domain of the channel by increasing the mechanical rigidity of the membrane; and (iii) DOTAP can reduce the effect of electrostatic forces by regulating the dielectric constant at the channel–lipid interface. The electromechanical model predictions for the three lipid types match well with the experimental observations and provide mechanistic insights into lipid-dependent gating of Kv channels. 

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5. Sterol–lipids enable large-scale, liquid–liquid phase separation in bilayer membranes of only two components

   https://doi.org/10.1073/pnas.2401241121  

   Wilson, Kent J; Nguyen, Huy Q; Gervay-Hague, Jacquelyn; Keller, Sarah L (September 2024, Proceedings of the National Academy of Sciences)

   Despite longstanding excitement and progress toward understanding liquid–liquid phase separation in natural and artificial membranes, fundamental questions have persisted about which molecules are required for this phenomenon. Except in extraordinary circumstances, the smallest number of components that has produced large-scale, liquid–liquid phase separation in bilayers has stubbornly remained at three: a sterol, a phospholipid with ordered chains, and a phospholipid with disordered chains. This requirement of three components is puzzling because only two components are required for liquid–liquid phase separation in lipid monolayers, which resemble half of a bilayer. Inspired by reports that sterols interact closely with lipids with ordered chains, we tested whether phase separation would occur in bilayers in which a sterol and lipid were replaced by a single, joined sterol–lipid. By evaluating a panel of sterol–lipids, some of which are present in bacteria, we found a minimal bilayer of only two components (PChemsPC and diPhyPC) that robustly demixes into micron-scale, liquid phases. It suggests an additional role for sterol–lipids in nature, and it reveals a membrane in which tie-lines (and, therefore, the lipid composition of each phase) are straightforward to determine and will be consistent across multiple laboratories. 

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