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International Journal of Molecular... Apr 2023Phafins are PH (Pleckstrin Homology) and FYVE (Fab1, YOTB, Vac1, and EEA1) domain-containing proteins. The Phafin protein family is classified into two groups based on... (Review)
Review
Phafins are PH (Pleckstrin Homology) and FYVE (Fab1, YOTB, Vac1, and EEA1) domain-containing proteins. The Phafin protein family is classified into two groups based on their sequence homology and functional similarity: Phafin1 and Phafin2. This protein family is unique because both the PH and FYVE domains bind to phosphatidylinositol 3-phosphate [PtdIns(3)P], a phosphoinositide primarily found in endosomal and lysosomal membranes. Phafin proteins act as PtdIns(3)P effectors in apoptosis, endocytic cargo trafficking, and autophagy. Additionally, Phafin2 is recruited to macropinocytic compartments through coincidence detection of PtdIns(3)P and PtdIns(4)P. Membrane-associated Phafins serve as adaptor proteins that recruit other binding partners. In addition to the phosphoinositide-binding domains, Phafin proteins present a poly aspartic acid motif that regulates membrane binding specificity. In this review, we summarize the involvement of Phafins in several cellular pathways and their potential physiological functions while highlighting the similarities and differences between Phafin1 and Phafin2. Besides, we discuss research perspectives for Phafins.
Topics: Carrier Proteins; Phosphatidylinositols; Phosphatidylinositol Phosphates; Intracellular Membranes; Apoptosis; Endosomes; Protein Binding
PubMed: 37175801
DOI: 10.3390/ijms24098096 -
Journal of Cell Science Mar 2022Lipid droplets (LDs) are ubiquitous organelles that store and supply lipids for energy metabolism, membrane synthesis and production of lipid-derived signaling...
Lipid droplets (LDs) are ubiquitous organelles that store and supply lipids for energy metabolism, membrane synthesis and production of lipid-derived signaling molecules. While compositional differences in the phospholipid monolayer or neutral lipid core of LDs impact their metabolism and function, the proteome of LDs has emerged as a major influencer in all aspects of LD biology. The perilipins (PLINs) are the most studied and abundant proteins residing on the LD surface. This Cell Science at a Glance and the accompanying poster summarize our current knowledge of the common and unique features of the mammalian PLIN family of proteins, the mechanisms through which they affect cell metabolism and signaling, and their links to disease.
Topics: Animals; Lipid Droplets; Lipid Metabolism; Mammals; Perilipins; Phospholipids; Protein Binding; Proteome
PubMed: 35260890
DOI: 10.1242/jcs.259501 -
ACS Chemical Biology Nov 2019Synthesis and regulation of lipid levels and identities is critical for a wide variety of cellular functions, including structural and morphological properties of... (Review)
Review
Synthesis and regulation of lipid levels and identities is critical for a wide variety of cellular functions, including structural and morphological properties of organelles, energy storage, signaling, and stability and function of membrane proteins. Proteolytic cleavage events regulate and/or influence some of these lipid metabolic processes and as a result help modulate their pleiotropic cellular functions. Proteins involved in lipid regulation are proteolytically cleaved for the purpose of their relocalization, processing, turnover, and quality control, among others. The scope of this review includes proteolytic events governing cellular lipid dynamics. After an initial discussion of the classic example of sterol regulatory element-binding proteins, our focus will shift to the mitochondrion, where a range of proteolytic events are critical for normal mitochondrial phospholipid metabolism and enforcing quality control therein. Recently, mitochondrial phospholipid metabolic pathways have been implicated as important for the proliferative capacity of cancers. Thus, the assorted proteases that regulate, monitor, or influence the activity of proteins that are important for phospholipid metabolism represent attractive targets to be manipulated for research purposes and clinical applications.
Topics: Animals; Cell Membrane; Cholesterol; Gene Expression Regulation; Humans; Lipid Metabolism; Mitochondria; Peptide Hydrolases; Phospholipids; Protein Binding; Protein Conformation; Proteolysis; Signal Transduction
PubMed: 31503446
DOI: 10.1021/acschembio.9b00695 -
Proceedings of the National Academy of... Oct 2023α-synuclein (α-Syn) is a presynaptic protein that is involved in Parkinson's and other neurodegenerative diseases and binds to negatively charged phospholipids....
α-synuclein (α-Syn) is a presynaptic protein that is involved in Parkinson's and other neurodegenerative diseases and binds to negatively charged phospholipids. Previously, we reported that α-Syn clusters synthetic proteoliposomes that mimic synaptic vesicles. This vesicle-clustering activity depends on a specific interaction of α-Syn with anionic phospholipids. Here, we report that α-Syn surprisingly also interacts with the neutral phospholipid lysophosphatidylcholine (lysoPC). Even in the absence of anionic lipids, lysoPC facilitates α-Syn-induced vesicle clustering but has no effect on Ca-triggered fusion in a single vesicle-vesicle fusion assay. The A30P mutant of α-Syn that causes familial Parkinson disease has a reduced affinity to lysoPC and does not induce vesicle clustering. Taken together, the α-Syn-lysoPC interaction may play a role in α-Syn function.
Topics: Humans; alpha-Synuclein; Synaptic Vesicles; Lysophosphatidylcholines; Parkinson Disease; Phospholipids
PubMed: 37883437
DOI: 10.1073/pnas.2310174120 -
The EMBO Journal May 2023The interferon-induced transmembrane proteins (IFITM) are implicated in several biological processes, including antiviral defense, but their modes of action remain...
The interferon-induced transmembrane proteins (IFITM) are implicated in several biological processes, including antiviral defense, but their modes of action remain debated. Here, taking advantage of pseudotyped viral entry assays and replicating viruses, we uncover the requirement of host co-factors for endosomal antiviral inhibition through high-throughput proteomics and lipidomics in cellular models of IFITM restriction. Unlike plasma membrane (PM)-localized IFITM restriction that targets infectious SARS-CoV2 and other PM-fusing viral envelopes, inhibition of endosomal viral entry depends on lysines within the conserved IFITM intracellular loop. These residues recruit Phosphatidylinositol 3,4,5-trisphosphate (PIP3) that we show here to be required for endosomal IFITM activity. We identify PIP3 as an interferon-inducible phospholipid that acts as a rheostat for endosomal antiviral immunity. PIP3 levels correlated with the potency of endosomal IFITM restriction and exogenous PIP3 enhanced inhibition of endocytic viruses, including the recent SARS-CoV2 Omicron variant. Together, our results identify PIP3 as a critical regulator of endosomal IFITM restriction linking it to the Pi3K/Akt/mTORC pathway and elucidate cell-compartment-specific antiviral mechanisms with potential relevance for the development of broadly acting antiviral strategies.
Topics: Humans; Antiviral Agents; Interferons; Phospholipids; Phosphatidylinositol 3-Kinases; RNA, Viral; RNA-Binding Proteins; COVID-19; SARS-CoV-2; Virus Internalization; Membrane Proteins
PubMed: 36970857
DOI: 10.15252/embj.2022112234 -
Traffic (Copenhagen, Denmark) Nov 2020This review considers the following hypotheses, some well-supported and some speculative. Almost all of the sterol molecules in plasma membranes are associated with... (Review)
Review
This review considers the following hypotheses, some well-supported and some speculative. Almost all of the sterol molecules in plasma membranes are associated with bilayer phospholipids in complexes of varied strength and stoichiometry. These complexes underlie many of the material properties of the bilayer. The small fraction of cholesterol molecules exceeding the binding capacity of the phospholipids is thermodynamically active and serves diverse functions. It circulates briskly among the cell membranes, particularly through contact sites linking the organelles. Active cholesterol provides the upstream feedback signal to multiple mechanisms governing plasma membrane homeostasis, pegging the sterol level to a threshold set by its phospholipids. Active cholesterol could also be the cargo for various inter-organelle transporters and the form excreted from cells by reverse transport. Furthermore, it is integral to the function of caveolae; a mediator of Hedgehog regulation; and a ligand for the binding of cytolytic toxins to membranes. Active cholesterol modulates a variety of plasma membrane proteins-receptors, channels and transporters-at least in vitro.
Topics: Caveolae; Cell Membrane; Cholesterol; Phospholipids; Sterols
PubMed: 32930466
DOI: 10.1111/tra.12762 -
Frontiers in Immunology 2023Macrophages are essential for the proper inflammatory and reparative processes that lead to regeneration of skeletal muscle after injury. Recent studies have...
Macrophages are essential for the proper inflammatory and reparative processes that lead to regeneration of skeletal muscle after injury. Recent studies have demonstrated close links between the function of activated macrophages and their cellular metabolism. Sterol regulatory element-binding protein 1 (SREBP1) is a key regulator of lipid metabolism and has been shown to affect the activated states of macrophages. However, its role in tissue repair and regeneration is poorly understood. Here we show that systemic deletion of , encoding SREBP1, or macrophage-specific deletion of , encoding SREBP1a, delays resolution of inflammation and impairs skeletal muscle regeneration after injury. deficiency impairs mitochondrial function in macrophages and suppresses the accumulation of macrophages at sites of muscle injury. Lipidomic analyses showed the reduction of major phospholipid species in muscle myeloid cells. Moreover, diet supplementation with eicosapentaenoic acid restored the accumulation of macrophages and their mitochondrial gene expression and improved muscle regeneration. Collectively, our results demonstrate that SREBP1 in macrophages is essential for repair and regeneration of skeletal muscle after injury and suggest that SREBP1-mediated fatty acid metabolism and phospholipid remodeling are critical for proper macrophage function in tissue repair.
Topics: Macrophages; Muscle, Skeletal; Phospholipids; Regeneration; Sterol Regulatory Element Binding Protein 1; Animals; Mice
PubMed: 38259495
DOI: 10.3389/fimmu.2023.1251784 -
Biochimica Et Biophysica Acta.... Jul 2022Adenosine triphosphate-binding cassette transporter subfamily A member 7 (ABCA7) performs incompletely understood biochemical functions that affect pathogenesis of...
Adenosine triphosphate-binding cassette transporter subfamily A member 7 (ABCA7) performs incompletely understood biochemical functions that affect pathogenesis of Alzheimer's disease. ABCA7 is most similar in primary structure to ABCA1, the protein that mediates cell lipid efflux and formation of high-density lipoprotein (HDL). Lipid metabolic labeling/tracer efflux assays were employed to investigate lipid efflux in BHK-ABCA7(low expression), BHK-ABCA7(high expression) and BHK-ABCA1 cells. Shotgun lipid mass spectrometry was used to determine lipid composition of HDL synthesized by BHK-ABCA7 and BHK-ABCA1 cells. BHK-ABCA7(low) cells exhibited significant efflux only of choline-phospholipid and phosphatidylinositol. BHK-ABCA7(high) cells had significant cholesterol and choline-phospholipid efflux to apolipoprotein (apo) A-I, apo E, the 18A peptide, HDL, plasma and cerebrospinal fluid and significant efflux of sphingosine-lipid, serine-lipid (which is composed of phosphatidylserine and phosphatidylethanolamine in BHK cells) and phosphatidylinositol to apo A-I. In efflux assays to apo A-I, after adjustment to choline-phospholipid, ABCA7-mediated efflux removed ~4 times more serine-lipid and phosphatidylinositol than ABCA1-mediated efflux, while ABCA1-mediated efflux removed ~3 times more cholesterol than ABCA7-mediated efflux. Shotgun lipidomic analysis revealed that ABCA7-HDL had ~20 mol% less phosphatidylcholine and 3-5 times more serine-lipid and phosphatidylinositol than ABCA1-HDL, while ABCA1-HDL contained only ~6 mol% (or ~1.1 times) more cholesterol than ABCA7-HDL. The discrepancy between the tracer efflux assays and shotgun lipidomics with respect to cholesterol may be explained by an underestimate of ABCA7-mediated cholesterol efflux in the former approach. Overall, these results suggest that ABCA7 lacks specificity for phosphatidylcholine and releases significantly but not dramatically less cholesterol in comparison with ABCA1.
Topics: ATP-Binding Cassette Transporters; Apolipoprotein A-I; Cholesterol; Choline; Lipoproteins, HDL; Phosphatidylcholines; Phosphatidylinositols; Phospholipids; Serine
PubMed: 35381375
DOI: 10.1016/j.bbalip.2022.159157 -
Molecules (Basel, Switzerland) Sep 2019Autotaxin (ATX) is an extracellular enzyme that hydrolyses lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA), which has a role in the mediation of...
Autotaxin (ATX) is an extracellular enzyme that hydrolyses lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA), which has a role in the mediation of inflammation, fibrosis and cancer. ATX is a drug target that has been the focus of many research groups during the last ten years. To date, only one molecule, Ziritaxestat (GLPG1690) has entered the clinic; it is currently in Phase 3 clinical trials for idiopathic pulmonary fibrosis. Other small molecules, with different binding modes, have been investigated as ATX inhibitors for cancer including compounds possessing a boronic acid motif such as HA155. In this work, we targeted new, improved inhibitors of ATX that mimic the important interactions of boronic acid using a benzoxaborole motif as the acidic warhead. Furthermore, we aimed to improve the plasma stability of the new compounds by using a more stable core spacer than that embedded in HA155. Compounds were synthesized, evaluated for their ATX inhibitory activity and ADME properties in vitro, culminating in a new benzoxaborole compound, 37, which retains the ATX inhibition activity of HA155 but has improved ADME properties (plasma protein binding, good kinetic solubility and rat/human plasma stability).
Topics: Animals; Humans; Lysophosphatidylcholines; Lysophospholipids; Neoplasms; Phosphoric Diester Hydrolases; Rats; Structure-Activity Relationship
PubMed: 31547058
DOI: 10.3390/molecules24193419 -
Biochemistry Dec 2021The G-protein-gated inwardly rectifying potassium channel 4 (Kir3.4) subunit forms functional tetramers. Previous studies have established that phosphatidylinositol...
The G-protein-gated inwardly rectifying potassium channel 4 (Kir3.4) subunit forms functional tetramers. Previous studies have established that phosphatidylinositol 4,5-bisphosphate (PI(4,5)P) is required for Kir3.4 function. However, the binding preferences of Kir3.4 for the headgroup and acyl chains of phosphorylated phosphatidylinositides (PIPs) and other lipids are not well understood. Here, the interactions between full-length, human Kir3.4 and lipids are characterized using native mass spectrometry (MS) in conjunction with a soluble fluorescent lipid-binding assay. Kir3.4 displays binding preferences for PIPs, and, in some cases, the degree of binding is influenced by the type of acyl chains. The interactions between Kir3.4 and PIPs are weaker in comparison to full-length, human Kir3.2. The binding of PI(4,5)P modified with a fluorophore to Kir3.2 can be enhanced by other lipids, such as phosphatidylcholine. Introduction of S143T, a mutation that enhances Kir3.4 activity, results in an overall reduction in the channel binding PIPs. In contrast, the D223N mutant of Kir3.4 that mimics the sodium-bound state exhibited stronger binding for PI(4,5)P, particularly for those with 18:0-20:4 acyl chains. Taken together, these results provide additional insight into the interaction between Kir3.4 and lipids that are important for channel function.
Topics: Amino Acid Substitution; Binding Sites; Binding, Competitive; Boron Compounds; Fluorescent Dyes; G Protein-Coupled Inwardly-Rectifying Potassium Channels; Humans; Models, Molecular; Phosphatidylinositols; Phospholipids; Point Mutation; Protein Binding; Protein Structure, Quaternary; Recombinant Proteins; Spectrometry, Mass, Electrospray Ionization
PubMed: 34846128
DOI: 10.1021/acs.biochem.1c00615