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Neuroscience Research Jun 2021Phospholipids are asymmetrically distributed at the plasma membrane. Phosphatidylserine (PtdSer) is exclusively located in the inner leaflet of the cell membrane while... (Review)
Review
Phospholipids are asymmetrically distributed at the plasma membrane. Phosphatidylserine (PtdSer) is exclusively located in the inner leaflet of the cell membrane while phosphatidylcholine (PtdCho) and glycolipids are mainly located in the outer leaflet of the membrane. However, this asymmetry is disrupted in various physiological situations, and PtdSer is exposed on the cell surface. In platelets, exposed PtdSer functions as a scaffold for the coagulation reaction, while in dead cells, exposed PtdSer serves as an "Eat-me" signal for efferocytosis. In the developing brain, synaptic connections are over-formed during the fetal period, but about half of the neurons are removed by apoptosis, and synaptic and dendritic compartments of living neurons are also removed by phagocytes. During these processes, glial cells such as microglia and astrocyte engulf unwanted dead cells and compartments in living cells using several phagocytic receptors, recognizing PtdSer by direct binding or an indirect way using secreted molecules. Based on recent findings, we will discuss how the compartments in living neurons are eliminated for the neuronal circuit plasticity.
Topics: Apoptosis; Brain; Cell Membrane; Phosphatidylserines; Phospholipids
PubMed: 33476682
DOI: 10.1016/j.neures.2021.01.003 -
Biomolecules Oct 2023Metazoan cell nuclei contain non-membrane pools of the phosphoinositide lipid PI(4,5)P2 (PIP2), but how this hydrophobic lipid exists within the aqueous nucleoplasm...
Metazoan cell nuclei contain non-membrane pools of the phosphoinositide lipid PI(4,5)P2 (PIP2), but how this hydrophobic lipid exists within the aqueous nucleoplasm remains unclear. Steroidogenic Factor-1 (NR5A1, SF-1) is a nuclear receptor that binds PIP2 in vitro, and a co-crystal structure of the complex suggests the acyl chains of PIP2 are hidden in the hydrophobic core of the SF-1 protein while the PIP2 headgroup is solvent-exposed. This binding mode explains how SF-1 can solubilize nuclear PIP2; however, cellular evidence that SF-1 expression associates with nuclear PIP2 has been lacking. Here, we examined if tetracycline induction of SF-1 expression would associate with nuclear accumulation of PIP2, using antibodies directed against the PIP2 headgroup. Indeed, tetracycline induction of wild-type SF-1 induced a signal in the nucleus of HEK cells that cross-reacts with PIP2 antibodies, but did not cross-react with antibodies against the lower abundance phosphoinositide PI(3,4,5)P3 (PIP3). The nuclear PIP2 signal co-localized with FLAG-tagged SF-1 in the nuclear compartment. To determine if the nuclear PIP2 signal was dependent on the ability of SF-1 to bind PIP2, we examined a "pocket mutant" of SF-1 (A270W, L345F) shown to be deficient in phospholipid binding by mass spectrometry. Tetracycline induction of this pocket mutant SF-1 in HEK cells failed to induce a detectable PIP2 antibody cross-reactive signal, despite similar Tet-induced expression levels of the wild-type and pocket mutant SF-1 proteins in these cells. Together, these data are the first to suggest that expression of SF-1 induces a PIP2 antibody cross-reactive signal in the nucleus, consistent with X-ray crystallographic and biochemical evidence suggesting SF-1 binds PIP2 in human cells.
Topics: Animals; Humans; Cell Nucleus; Phosphatidylinositols; Receptors, Cytoplasmic and Nuclear; Tetracyclines; Steroidogenic Factor 1
PubMed: 37892191
DOI: 10.3390/biom13101509 -
Langmuir : the ACS Journal of Surfaces... Aug 2022Liposomes represent important drug carrier vehicles in biological systems. A fusogenic liposomal system composed of equimolar mixtures of the cationic lipid DOTAP and...
Liposomes represent important drug carrier vehicles in biological systems. A fusogenic liposomal system composed of equimolar mixtures of the cationic lipid DOTAP and the phospholipid DOPE showed high fusion and delivery efficiencies with cells and lipid vesicles. However, aspects of the thermodynamics involving the interaction of these fusogenic liposomes and biomimetic systems remain unclear. Here, we investigate the fusion of this system with large unilamellar vesicles (LUVs) composed of the zwitterionic lipid POPC and increasing fractions of the anionic lipid POPG and up to 30 mol % cholesterol. The focus here is to concomitantly follow changes in size, zeta-potential, and enthalpy binding upon membrane interaction and fusion. Isothermal titration calorimetry (ITC) data showed that membrane fusion in our system is an exothermic process in the absence of cholesterol, suggesting that electrostatic attraction is the driving force for fusion. An endothermic component appeared and eventually dominated the titration at 30 mol % cholesterol, which we propose is caused by membrane fluidification when cholesterol is diluted upon fusion. The inflection points of the ITC data occurred around 0.5-0.7 POPG/DOTAP for all systems, the same stoichiometry for which zeta-potential and dynamic light scattering measurements showed an increase in size coupled with charge neutralization of the system, which is consistent with the fact that fusion in our system is charge-mediated. Microscopy observations of the final mixtures revealed the presence of giant vesicles, which is a clear indication of fusion, coexisting with intermediate-sized objects that could be the result of both fusion and/or aggregation. The results show that the fusion efficiency of the DOTAP:DOPE fusogenic system is modulated by the charge and membrane packing of the acceptor membrane and explain why the system fuses very efficiently with cells.
Topics: Calorimetry; Cholesterol; Liposomes; Membrane Fusion; Phospholipids; Unilamellar Liposomes
PubMed: 35977420
DOI: 10.1021/acs.langmuir.2c01169 -
Cell Chemical Biology Jul 2022Phospholipids are ligands for nuclear hormone receptors (NRs) that regulate transcriptional programs relevant to normal physiology and disease. Here, we demonstrate that...
Phospholipids are ligands for nuclear hormone receptors (NRs) that regulate transcriptional programs relevant to normal physiology and disease. Here, we demonstrate that mimicking phospholipid-NR interactions is a robust strategy to improve agonists of liver receptor homolog-1 (LRH-1), a therapeutic target for colitis. Conventional LRH-1 modulators only partially occupy the binding pocket, leaving vacant a region important for phospholipid binding and allostery. Therefore, we constructed a set of molecules with elements of natural phospholipids appended to a synthetic LRH-1 agonist. We show that the phospholipid-mimicking groups interact with the targeted residues in crystal structures and improve binding affinity, LRH-1 transcriptional activity, and conformational changes at a key allosteric site. The best phospholipid mimetic markedly improves colonic histopathology and disease-related weight loss in a murine T cell transfer model of colitis. This evidence of in vivo efficacy for an LRH-1 modulator in colitis represents a leap forward in agonist development.
Topics: Animals; Colitis; Ligands; Mice; Phospholipids; Receptors, Cytoplasmic and Nuclear
PubMed: 35316658
DOI: 10.1016/j.chembiol.2022.03.001 -
Emerging Topics in Life Sciences Mar 2023Eukaryotic pathogens with an intracellular parasitic lifestyle are shielded from extracellular threats during replication and growth. In addition to many nutrients,... (Review)
Review
Eukaryotic pathogens with an intracellular parasitic lifestyle are shielded from extracellular threats during replication and growth. In addition to many nutrients, parasites scavenge host cell lipids to establish complex membrane structures inside their host cells. To counteract the disturbance of the host cell plasma membrane they have evolved strategies to regulate phospholipid asymmetry. In this review, the function and importance of lipid asymmetry in the interactions of intracellular protozoan parasites with the target and immune cells of the host are highlighted. The malaria parasite Plasmodium infects red blood cells and extensively refurbishes these terminally differentiated cells. Cholesterol depletion and an altered intracellular calcium ion homeostasis can lead to disruption in erythrocyte membrane asymmetry and increased exposure of phosphatidylserine (PS). Binding to the PS receptor on monocytes and macrophages results in phagocytosis and destruction of infected erythrocytes. Leishmania parasites display apoptotic mimicry by actively enhancing PS exposure on their surface to trigger increased infection of macrophages. In extracellular Toxoplasma gondii a P4-type ATPase/CDC50 co-chaperone pair functions as a flippase important for exocytosis of specialised secretory organelles. Identification and functional analysis of parasite lipid-translocating proteins, i.e. flippases, floppases, and scramblases, will be central for the recognition of the molecular mechanisms of parasite/host interactions. Ultimately, a better understanding of parasitic diseases, host immunity, and immune escape by parasites require more research on the dynamics of phospholipid bilayers of parasites and the infected host cell.
Topics: Animals; Host-Parasite Interactions; Phospholipids; Parasites; Toxoplasma; Eukaryota
PubMed: 36820809
DOI: 10.1042/ETLS20220089 -
Nature Aug 2020Stimulation of the metabotropic GABA receptor by γ-aminobutyric acid (GABA) results in prolonged inhibition of neurotransmission, which is central to brain physiology....
Stimulation of the metabotropic GABA receptor by γ-aminobutyric acid (GABA) results in prolonged inhibition of neurotransmission, which is central to brain physiology. GABA belongs to family C of the G-protein-coupled receptors, which operate as dimers to transform synaptic neurotransmitter signals into a cellular response through the binding and activation of heterotrimeric G proteins. However, GABA is unique in its function as an obligate heterodimer in which agonist binding and G-protein activation take place on distinct subunits. Here we present cryo-electron microscopy structures of heterodimeric and homodimeric full-length GABA receptors. Complemented by cellular signalling assays and atomistic simulations, these structures reveal that extracellular loop 2 (ECL2) of GABA has an essential role in relaying structural transitions by ordering the linker that connects the extracellular ligand-binding domain to the transmembrane region. Furthermore, the ECL2 of each of the subunits of GABA caps and interacts with the hydrophilic head of a phospholipid that occupies the extracellular half of the transmembrane domain, thereby providing a potentially crucial link between ligand binding and the receptor core that engages G proteins. These results provide a starting framework through which to decipher the mechanistic modes of signal transduction mediated by GABA dimers, and have important implications for rational drug design that targets these receptors.
Topics: Binding Sites; Cell Membrane; Cryoelectron Microscopy; GABA-B Receptor Antagonists; Humans; Hydrophobic and Hydrophilic Interactions; Ligands; Models, Molecular; Phospholipids; Protein Domains; Protein Multimerization; Protein Subunits; Receptors, GABA-B; Receptors, Glutamate; Signal Transduction; Structure-Activity Relationship
PubMed: 32580208
DOI: 10.1038/s41586-020-2469-4 -
The Journal of Membrane Biology Dec 2020Spectrin is a multifunctional, multi-domain protein most well known in the membrane skeleton of mature human erythrocytes. Here we review the literature on the crosstalk... (Review)
Review
Spectrin is a multifunctional, multi-domain protein most well known in the membrane skeleton of mature human erythrocytes. Here we review the literature on the crosstalk of the chaperone activity of spectrin with its other functionalities. We hypothesize that the chaperone activity is derived from the surface exposed hydrophobic patches present in individual "spectrin-repeat" domains and show a competition between the membrane phospholipid binding functionality and chaperone activity of spectrin. Moreover, we show that post-translational modifications such as glycation which shield these surface exposed hydrophobic patches, reduce the chaperone function. On the other hand, oligomerization which is linked to increase of hydrophobicity is seen to increase it. We note that spectrin seems to prefer haemoglobin as its chaperone client, binding with it preferentially over other denatured proteins. Spectrin is also known to interact with unstable haemoglobin variants with a higher affinity than in the case of normal haemoglobin. We propose that chaperone activity of spectrin could be important in the cellular biochemistry of haemoglobin, particularly in the context of diseases.
Topics: Animals; Erythrocyte Membrane; Hemoglobins; Humans; Hydrophobic and Hydrophilic Interactions; Membrane Proteins; Molecular Chaperones; Phospholipids; Protein Binding; Protein Processing, Post-Translational; Spectrin
PubMed: 32990795
DOI: 10.1007/s00232-020-00142-1 -
Current Protein & Peptide Science 2022ATP-binding cassette subfamily A member 1 (ABCA1) protein plays an essential role in a variety of events, such as cholesterol and phospholipid efflux, nascent... (Review)
Review
ATP-binding cassette subfamily A member 1 (ABCA1) protein plays an essential role in a variety of events, such as cholesterol and phospholipid efflux, nascent high-density lipoprotein (HDL) biosynthesis, phospholipid translocation. Thus, there has been much research activity aimed at understanding the molecular mechanisms of regulating ABCA1 expression. In this review, we first discuss ABCA1 structure, tissue distribution, cellular localization, and trafficking, as well as its function. Furthermore, current understanding of the molecular mechanisms involved in the regulation of ABCA1 expression is summarized. ABCA1 transcriptional regulation is mediated by a very complicated system, including nuclear receptor systems, factors binding to other sites in the ABCA1 promoter, cytokines, hormones, growth factors, lipid metabolites, enzymes, and other messengers/factors/pathways. In addition, ABCA1 posttranscriptional regulation is mediated by microRNA, long noncoding RNA, RNA-binding proteins, proteases, fatty acids, PDZ proteins, signaling proteins, and other factors. Compared to the transcriptional regulation of ABCA1, which is well established, the post-transcriptional regulation of ABCA1 expression is poorly understood.
Topics: ATP-Binding Cassette Transporters; Cholesterol; Gene Expression Regulation; Lipoproteins, HDL; Phospholipids
PubMed: 35848568
DOI: 10.2174/1389203723666220429083753 -
The Journal of Physical Chemistry. B May 2023In this work, the influence of membrane curvature on the Ca binding to phospholipid bilayers is investigated by means of molecular dynamics simulations. In particular,...
In this work, the influence of membrane curvature on the Ca binding to phospholipid bilayers is investigated by means of molecular dynamics simulations. In particular, we compared Ca binding to flat, elastically buckled, or uniformly bent zwitterionic and anionic phospholipid bilayers. We demonstrate that Ca ions bind preferably to the concave membrane surfaces in both types of bilayers. We also show that the membrane curvature leads to pronounced changes in Ca binding including differences in free ion concentrations, lipid coordination distributions, and the patterns of ion binding to different chemical groups of lipids. Moreover, these effects differ substantially for the concave and convex membrane monolayers. Comparison between force fields with either full or scaled charges indicates that charge scaling results in reduction of the Ca binding to curved phosphatidylserine bilayers, while for phosphatidylcholine membranes, calcium binds only weakly for both force fields.
Topics: Phospholipids; Lipid Bilayers; Calcium; Molecular Dynamics Simulation; Phosphatidylcholines; Ions
PubMed: 37191140
DOI: 10.1021/acs.jpcb.3c01962 -
Nature Communications Nov 2023Asymmetric distribution of phospholipids in eukaryotic membranes is essential for cell integrity, signaling pathways, and vesicular trafficking. P4-ATPases, also known...
Asymmetric distribution of phospholipids in eukaryotic membranes is essential for cell integrity, signaling pathways, and vesicular trafficking. P4-ATPases, also known as flippases, participate in creating and maintaining this asymmetry through active transport of phospholipids from the exoplasmic to the cytosolic leaflet. Here, we present a total of nine cryo-electron microscopy structures of the human flippase ATP8B1-CDC50A complex at 2.4 to 3.1 Å overall resolution, along with functional and computational studies, addressing the autophosphorylation steps from ATP, substrate recognition and occlusion, as well as a phosphoinositide binding site. We find that the P4-ATPase transport site is occupied by water upon phosphorylation from ATP. Additionally, we identify two different autoinhibited states, a closed and an outward-open conformation. Furthermore, we identify and characterize the PI(3,4,5)P binding site of ATP8B1 in an electropositive pocket between transmembrane segments 5, 7, 8, and 10. Our study also highlights the structural basis of a broad lipid specificity of ATP8B1 and adds phosphatidylinositol as a transport substrate for ATP8B1. We report a critical role of the sn-2 ester bond of glycerophospholipids in substrate recognition by ATP8B1 through conserved S403. These findings provide fundamental insights into ATP8B1 catalytic cycle and regulation, and substrate recognition in P4-ATPases.
Topics: Humans; Adenosine Triphosphatases; Substrate Specificity; Cryoelectron Microscopy; Phospholipid Transfer Proteins; Phospholipids; Adenosine Triphosphate; Cell Membrane
PubMed: 37980352
DOI: 10.1038/s41467-023-42828-9