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Current Eye Research Feb 2021: The amount of membrane-bound α-crystallin increases significantly with age and cataract formation, accompanied by a corresponding decline in the level of...
: The amount of membrane-bound α-crystallin increases significantly with age and cataract formation, accompanied by a corresponding decline in the level of α-crystallin in the lens cytoplasm. The purpose of this research is to evaluate the binding affinity of α-crystallin to the phospholipid membranes as well as the physical properties of the membranes after α-crystallin binding. : The continuous wave and saturation recovery electron paramagnetic resonance (EPR) methods were used to obtain the information about the binding affinity and the physical properties of the membrane. In this approach, the cholesterol analog spin label CSL was incorporated in the membrane and the binding of α-crystallin to the membrane was monitored by this spin label. Small uni-lamellar vesicles were prepared from 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) with 1% of CSL. The measured membrane properties included the mobility parameter, fluidity, and the oxygen transport parameter. : The binding affinity ( ) of α-crystallin with the POPC membrane was estimated to be 4.9 ± 2.4 µM. The profiles of mobility parameter showed that mobility parameter decreased with an increase in the binding of α-crystallin. The profiles of spin-lattice relaxation rate showed that the spin-lattice relaxation rate decreased with an increase in binding. These results show that the binding of α-crystallin makes the membrane more immobilized near the head group region of the phospholipids. Furthermore, the profiles of the oxygen transport parameter indicated that the oxygen transport parameter decreased with an increase of binding, indicating the binding of α-crystallin forms a barrier for the passage of non-polar molecules which supports the barrier hypothesis. : The binding of α-crystallin to the membrane alters the physical properties of the membranes, and this plays a significant role in modulating the integrity of the membranes. EPR techniques are useful in studying α-crystallin membrane interactions.
Topics: Cataract; Electron Spin Resonance Spectroscopy; Humans; Lens, Crystalline; Phospholipids; Spin Labels; alpha-Crystallins
PubMed: 32564617
DOI: 10.1080/02713683.2020.1786131 -
Trends in Cell Biology Nov 2020Cardiolipin (CL) is a tetra-acylated diphosphatidylglycerol lipid. In physiological conditions, CL presents unsaturated chains and is located in the inner mitochondria... (Review)
Review
Cardiolipin (CL) is a tetra-acylated diphosphatidylglycerol lipid. In physiological conditions, CL presents unsaturated chains and is located in the inner mitochondria membrane (IMM). Dead signals, infection, or disease may change the level of CL saturation and oxidation and cause its translocation to the cytosolic side of the outer mitochondrial membrane (OMM), affecting mitochondrial function and the inflammatory response. In this review, we summarize the emerging proapoptotic, pro-, and anti-inflammatory functions of cytosolic-exposed CL and how they are regulated by CL chain saturation and oxidation. We underline how the unique dimeric phospholipid structure confers peculiar properties on CL in the regulation of cell death and immune system proteins, such as the Nucleotide-binding domain and leucine-rich repeat-containing pyrin protein 3 (NLRP3), caspases (Casp), and Toll-like receptor 4 (TLR4). We also provide an overview of the human diseases in which CL deficiency or modification are implicated and of the use of exogenous unsaturated CL (uCL) as a novel therapeutic approach.
Topics: Animals; Anti-Inflammatory Agents; Cardiolipins; Cell Death; Humans; Immunity, Innate; Mitochondria; Signal Transduction
PubMed: 33011017
DOI: 10.1016/j.tcb.2020.09.004 -
Journal of Lipid Research 2021The field of phosphoinositide signaling has expanded significantly in recent years. Phosphoinositides (also known as phosphatidylinositol phosphates or PIPs) are... (Review)
Review
The field of phosphoinositide signaling has expanded significantly in recent years. Phosphoinositides (also known as phosphatidylinositol phosphates or PIPs) are universal signaling molecules that directly interact with membrane proteins or with cytosolic proteins containing domains that directly bind phosphoinositides and are recruited to cell membranes. Through the activities of phosphoinositide kinases and phosphoinositide phosphatases, seven distinct phosphoinositide lipid molecules are formed from the parent molecule, phosphatidylinositol. PIP signals regulate a wide range of cellular functions, including cytoskeletal assembly, membrane budding and fusion, ciliogenesis, vesicular transport, and signal transduction. Given the many excellent reviews on phosphoinositide kinases, phosphoinositide phosphatases, and PIPs in general, in this review, we discuss recent studies and advances in PIP lipid signaling in the retina. We specifically focus on PIP lipids from vertebrate (e.g., bovine, rat, mouse, toad, and zebrafish) and invertebrate (e.g., Drosophila, horseshoe crab, and squid) retinas. We also discuss the importance of PIPs revealed from animal models and human diseases, and methods to study PIP levels both in vitro and in vivo. We propose that future studies should investigate the function and mechanism of activation of PIP-modifying enzymes/phosphatases and further unravel PIP regulation and function in the different cell types of the retina.
Topics: Phosphatidylinositols
PubMed: 32540927
DOI: 10.1194/jlr.TR120000806 -
International Journal of Molecular... Dec 2019Unconventional myosins are multi-potent molecular motors that are assigned important roles in fundamental cellular processes. Depending on their mechano-enzymatic... (Review)
Review
Unconventional myosins are multi-potent molecular motors that are assigned important roles in fundamental cellular processes. Depending on their mechano-enzymatic properties and structural features, myosins fulfil their roles by acting as cargo transporters along the actin cytoskeleton, molecular anchors or tension sensors. In order to perform such a wide range of roles and modes of action, myosins need to be under tight regulation in time and space. This is achieved at multiple levels through diverse regulatory mechanisms: the alternative splicing of various isoforms, the interaction with their binding partners, their phosphorylation, their applied load and the composition of their local environment, such as ions and lipids. This review summarizes our current knowledge of how unconventional myosins are regulated, how these regulatory mechanisms can adapt to the specific features of a myosin and how they can converge with each other in order to ensure the required tight control of their function.
Topics: Actins; Alternative Splicing; Animals; Humans; Myosins; Phospholipids; Phosphorylation; Protein Interaction Maps; Protein Isoforms; Protein Multimerization
PubMed: 31861842
DOI: 10.3390/ijms21010067 -
Journal of the American Chemical Society Apr 2022TRAAK and TREK2 are two-pore domain K (K2P) channels and are modulated by diverse factors including temperature, membrane stretching, and lipids, such as phosphatidic...
TRAAK and TREK2 are two-pore domain K (K2P) channels and are modulated by diverse factors including temperature, membrane stretching, and lipids, such as phosphatidic acid. In addition, copper and zinc, both of which are essential for life, are known to regulate TREK2 and a number of other ion channels. However, the role of ions in the association of lipids with integral membrane proteins is poorly understood. Here, we discover cupric ions selectively modulate the binding of phosphatidylserine (PS) to TRAAK but not TREK2. Other divalent cations (Ca, Mg, and Zn) bind both channels but have no impact on binding PS and other lipids. Additionally, TRAAK binds more avidly to Cu and Zn than TREK2. In the presence of Cu, TRAAK binds similarly to PS with different acyl chains, indicating a crucial role of the serine headgroup in coordinating Cu. High-resolution native mass spectrometry (MS) enables the determination of equilibrium binding constants for distinct Cu-bound stoichiometries and uncovered the highest coupling factor corresponds to a 1:1 PS-to-Cu ratio. Interestingly, the next three highest coupling factors had a ∼1.5:1 PS-to-Cu ratio. Our findings bring forth the role of cupric ions as an essential cofactor in selective TRAAK-PS interactions.
Topics: Cations, Divalent; Phosphatidylserines; Potassium Channels, Tandem Pore Domain
PubMed: 35421309
DOI: 10.1021/jacs.2c00612 -
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 -
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 -
Viruses Mar 2022HIV-1 viral particle assembly occurs specifically at the plasma membrane and is driven primarily by the viral polyprotein Gag. Selective association of Gag with the... (Review)
Review
HIV-1 viral particle assembly occurs specifically at the plasma membrane and is driven primarily by the viral polyprotein Gag. Selective association of Gag with the plasma membrane is a key step in the viral assembly pathway, which is traditionally attributed to the MA domain. MA regulates specific plasma membrane binding through two primary mechanisms including: (1) specific interaction of the MA highly basic region (HBR) with the plasma membrane phospholipid phosphatidylinositol (4,5) bisphosphate [PI(4,5)P], and (2) tRNA binding to the MA HBR, which prevents Gag association with non-PI(4,5)P containing membranes. Gag multimerization, driven by both CA-CA inter-protein interactions and NC-RNA binding, also plays an essential role in viral particle assembly, mediating the establishment and growth of the immature Gag lattice on the plasma membrane. In addition to these functions, the multimerization of HIV-1 Gag has also been demonstrated to enhance its membrane binding activity through the MA domain. This review provides an overview of the mechanisms regulating Gag membrane binding through the MA domain and multimerization through the CA and NC domains, and examines how these two functions are intertwined, allowing for multimerization mediated enhancement of Gag membrane binding.
Topics: Cell Membrane; HIV-1; Membranes; Phosphatidylinositol 4,5-Diphosphate; Protein Binding; Virus Assembly; gag Gene Products, Human Immunodeficiency Virus
PubMed: 35337029
DOI: 10.3390/v14030622 -
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