scholarly journals Role of chirality in peptide-induced formation of cholesterol-rich domains

2005 ◽  
Vol 390 (2) ◽  
pp. 541-548 ◽  
Author(s):  
Richard M. Epand ◽  
Scott D. Rychnovsky ◽  
Jitendra D. Belani ◽  
Raquel F. Epand
Keyword(s):  
Membrane Lipids ◽  
Specific Binding ◽  
Binding Pocket ◽  
Small Peptides ◽  
Axonal Membrane ◽  
Lipid Mixture ◽  
Transition Enthalpy ◽  
Lipid Organization ◽  
Chiral Specificity

The chiral specificity of the interactions of peptides that induce the formation of cholesterol-rich domains has not been extensively investigated. Both the peptide and most lipids are chiral, so there is a possibility that interactions between peptide and lipid could require chiral recognition. On the other hand, in our models with small peptides, the extent of folding of the peptide to form a specific binding pocket is limited. We have determined that replacing cholesterol with its enantiomer, ent-cholesterol, alters the modulation of lipid organization by peptides. The phase-transition properties of SOPC (1-stearoyl-2-oleoylphosphatidylcholine):cholesterol [in a 6:4 ratio with 0.2 mol% PtdIns(4,5)P2] are not significantly altered when ent-cholesterol replaces cholesterol. However, in the presence of 10 mol% of a 19-amino-acid, N-terminally myristoylated fragment (myristoyl-GGKLSKKKKGYNVNDEKAK-amide) of the protein NAP-22 (neuronal axonal membrane protein), the lipid mixture containing cholesterol undergoes separation into cholesterol-rich and cholesterol-depleted domains. This does not occur when ent-cholesterol replaces cholesterol. In another example, when N-acetyl-Leu-Trp-Tyr-Ile-Lys-amide (N-acetyl-LWYIK-amide) is added to SOPC:cholesterol (7:3 ratio), there is a marked increase in the transition enthalpy of the phospholipid, indicating separation of a cholesterol-depleted domain of SOPC. This phenomenon completely disappears when ent-cholesterol replaces cholesterol. The all-D-isomer of N-acetyl-LWYIK-amide also induces the formation of cholesterol-rich domains with natural cholesterol, but does so to a lesser extent with ent-cholesterol. Thus specific peptide chirality is not required for interaction with cholesterol-containing membranes. However, a specific chirality of membrane lipids is required for peptide-induced formation of cholesterol-rich domains.

scholarly journals The role of neutral lipid nanospheres in Plasmodium falciparum haem crystallization

2007 ◽  
Vol 402 (1) ◽  
pp. 197-204 ◽  
Author(s):  
John M. Pisciotta ◽  
Isabelle Coppens ◽  
Abhai K. Tripathi ◽  
Peter F. Scholl ◽  
Joel Shuman ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Neutral Lipid ◽  
Membrane Lipids ◽  
Neutral Lipids ◽  
Close Association ◽  
Subcellular Fractionation ◽  
Digestive Vacuole ◽  
Lipid Mixture ◽  
Intracellular Mechanism

The intraerythrocytic malaria parasite constructs an intracellular haem crystal, called haemozoin, within an acidic digestive vacuole where haemoglobin is degraded. Haem crystallization is the target of the widely used antimalarial quinoline drugs. The intracellular mechanism of molecular initiation of haem crystallization, whether by proteins, polar membrane lipids or by neutral lipids, has not been fully substantiated. In the present study, we show neutral lipid predominant nanospheres, which envelop haemozoin inside Plasmodium falciparum digestive vacuoles. Subcellular fractionation of parasite-derived haemozoin through a dense 1.7 M sucrose cushion identifies monoacylglycerol and diacylglycerol neutral lipids as well as some polar lipids in close association with the purified haemozoin. Global MS lipidomics detects monopalmitic glycerol and monostearic glycerol, but not mono-oleic glycerol, closely associated with haemozoin. The complex neutral lipid mixture rapidly initiates haem crystallization, with reversible pH-dependent quinoline inhibition associated with quinoline entry into the neutral lipid microenvironment. Neutral lipid nanospheres both enable haem crystallization in the presence of high globin concentrations and protect haem from H2O2 degradation. Conceptually, the present study shifts the intracellular microenvironment of haem crystallization and quinoline inhibition from a polar aqueous location to a non-polar neutral lipid nanosphere able to exclude water for efficient haem crystallization.

On the Role of Transferrin in 67Ga Uptake by Tumor Cells

1988 ◽  
Vol 27 (04) ◽  
pp. 151-153
Author(s):  
P. Thouvenot ◽  
F. Brunotte ◽  
J. Robert ◽  
L. J. Anghileri
Keyword(s):  
Specific Binding ◽  
Subcellular Fractionation ◽  
Animal Blood ◽  
Tumor Bearing ◽  
Cell Structures ◽  
The Difference ◽  
Sarcoma Cells ◽  
In Vitro Uptake

In vitro uptake of 67Ga-citrate and 59Fe-citrate by DS sarcoma cells in the presence of tumor-bearing animal blood plasma showed a dramatic inhibition of both 67Ga and 59Fe uptakes: about ii/io of 67Ga and 1/5o of the 59Fe are taken up by the cells. Subcellular fractionation appears to indicate no specific binding to cell structures, and the difference of binding seems to be related to the transferrin chelation and transmembrane transport differences

The Role of Lipids and Membranes in the Pathogenesis of Alzheimer's Disease: A Comprehensive View

2018 ◽  
Vol 15 (13) ◽  
pp. 1191-1212 ◽  
Author(s):  
Botond Penke ◽  
Gábor Paragi ◽  
János Gera ◽  
Róbert Berkecz ◽  
Zsolt Kovács ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Signaling Pathways ◽  
Membrane Lipids ◽  
Specific Protein ◽  
Dietary Factors ◽  
Lipid Signaling ◽  
Special Role ◽  
Aβ Peptides

Lipids participate in Amyloid Precursor Protein (APP) trafficking and processing - important factors in the initiation of Alzheimer’s disease (AD) pathogenesis and influence the formation of neurotoxic β-amyloid (Aβ) peptides. An important risk factor, the presence of ApoE4 protein in AD brain cells binds the lipids to AD. In addition, lipid signaling pathways have a crucial role in the cellular homeostasis and depend on specific protein-lipid interactions. The current review focuses on pathological alterations of membrane lipids (cholesterol, glycerophospholipids, sphingolipids) and lipid metabolism in AD and provides insight in the current understanding of biological membranes, their lipid structures and functions, as well as their role as potential therapeutic targets. Novel methods for studying the membrane structure and lipid composition will be reviewed in a broad sense whereas the use of lipid biomarkers for early diagnosis of AD will be shortly summarized. Interactions of Aβ peptides with the cell membrane and different subcellular organelles are reviewed. Next, the details of the most important lipid signaling pathways, including the role of the plasma membrane as stress sensor and its therapeutic applications are given. 4-hydroxy-2-nonenal may play a special role in the initiation of the pathogenesis of AD and thus the “calpain-cathepsin hypothesis” of AD is highlighted. Finally, the most important lipid dietary factors and their possible use and efficacy in the prevention of AD are discussed.

scholarly journals Role of endosomal membrane lipids and NPC2 in cholesterol transfer and membrane fusion

2010 ◽  
Vol 51 (7) ◽  
pp. 1747-1760 ◽  
Author(s):  
Misbaudeen Abdul-Hammed ◽  
Bernadette Breiden ◽  
Matthew A. Adebayo ◽  
Jonathan O. Babalola ◽  
Günter Schwarzmann ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Membrane Lipids ◽  
Endosomal Membrane

scholarly journals Identification of Tyr residues that enhance folate substrate binding and constrain oscillation of the proton-coupled folate transporter (PCFT-SLC46A1)

2015 ◽  
Vol 308 (8) ◽  
pp. C631-C641 ◽  
Author(s):  
Michele Visentin ◽  
Ersin Selcuk Unal ◽  
Mitra Najmi ◽  
Andras Fiser ◽  
Rongbao Zhao ◽  
...  
Keyword(s):  
Choroid Plexus ◽  
Rate Constant ◽  
Binding Pocket ◽  
Wild Type ◽  
Efflux Rate ◽  
High Affinity ◽  
Extracellular Compartment ◽  
Efflux Rate Constant ◽  
Opposite Compartment

The proton-coupled folate transporter (PCFT) mediates intestinal folate absorption and transport of folates across the choroid plexus. This study focuses on the role of Tyr residues in PCFT function. The substituted Cys-accessibility method identified four Tyr residues (Y291, Y362, Y315, and Y414) that are accessible to the extracellular compartment; three of these (Y291, Y362, and Y315) are located within or near the folate binding pocket. When the Tyr residues were replaced with Cys or Ala, these mutants showed similar (up to 6-fold) increases in influx Vmax and Kt/ Ki for [3H]methotrexate and [3H]pemetrexed. When the Tyr residues were replaced with Phe, these changes were moderated or absent. When Y315A PCFT was used as representative of the mutants and [3H]pemetrexed as the transport substrate, this substitution did not increase the efflux rate constant. Furthermore, neither influx nor efflux mediated by Y315A PCFT was transstimulated by the presence of substrate in the opposite compartment; however, substantial bidirectional transstimulation of transport was mediated by wild-type PCFT. This resulted in a threefold greater efflux rate constant for cells that express wild-type PCFT than for cells that express Y315 PCFT under exchange conditions. These data suggest that these Tyr residues, possibly through their rigid side chains, secure the carrier in a high-affinity state for its folate substrates. However, this may be achieved at the expense of constraining the carrier's mobility, thereby decreasing the rate at which the protein oscillates between its conformational states. The Vmax generated by these Tyr mutants may be so rapid that further augmentation during transstimulation may not be possible.

How do mechanosensitive channels sense membrane tension?

2016 ◽  
Vol 44 (4) ◽  
pp. 1019-1025 ◽  
Author(s):  
Tim Rasmussen
Keyword(s):  
Membrane Lipids ◽  
Osmotic Shock ◽  
Md Simulations ◽  
Fatty Acyl ◽  
Membrane Bilayer ◽  
Cross Sectional ◽  
Conducting Path ◽  
Lipid Chain ◽  
Acyl Chains

Mechanosensitive (MS) channels provide protection against hypo-osmotic shock in bacteria whereas eukaryotic MS channels fulfil a multitude of important functions beside osmoregulation. Interactions with the membrane lipids are responsible for the sensing of mechanical force for most known MS channels. It emerged recently that not only prokaryotic, but also eukaryotic, MS channels are able to directly sense the tension in the membrane bilayer without any additional cofactor. If the membrane is solely viewed as a continuous medium with specific anisotropic physical properties, the sensitivity towards tension changes can be explained as result of the hydrophobic coupling between membrane and transmembrane (TM) regions of the channel. The increased cross-sectional area of the MS channel in the active conformation and elastic deformations of the membrane close to the channel have been described as important factors. However, recent studies suggest that molecular interactions of lipids with the channels could play an important role in mechanosensation. Pockets in between TM helices were identified in the MS channel of small conductance (MscS) and YnaI that are filled with lipids. Less lipids are present in the open state of MscS than the closed according to MD simulations. Thus it was suggested that exclusion of lipid fatty acyl chains from these pockets, as a consequence of increased tension, would trigger gating. Similarly, in the eukaryotic MS channel TRAAK it was found that a lipid chain blocks the conducting path in the closed state. The role of these specific lipid interactions in mechanosensation are highlighted in this review.

Variability in Anticardiolipin Antibody Detection: Role of Nonspecific IgG Binding and Different Microtiter Plates

2007 ◽  
Vol 13 (4) ◽  
pp. 404-409 ◽  
Author(s):  
Nelly M. Pellegrino ◽  
Domenico Caccavo
Keyword(s):  
Specific Binding ◽  
Anticardiolipin Antibody ◽  
Anticardiolipin Antibodies ◽  
Antibody Detection ◽  
Categorical Variables ◽  
Enzyme Linked Immunosorbent Assay ◽  
Microtiter Plates ◽  
Igg Binding ◽  
Coefficient Of Concordance

There are many studies that are available on the Internet that attempt to standardize the assay for anticardiolipin antibody evaluation because of the variability of results. The aim of this study was to evaluate simultaneously the role of different microplates and the importance of sample nonspecific binding in determining different results in anticardiolipin antibody detection. Sera from 8 patients with raised levels of IgG anticardiolipin antibodies and 10 control sera were assayed by enzyme-linked immunosorbent assay in the presence (specific binding) or in the absence of cardiolipin (sample blank) with four different microplates, that is, NUNC PolySorp, FALCON ProBIND, Greiner 655061 (high binding), and Greiner 655001 (medium binding). Results were expressed as optical densities or net-optical densities (following sample blank subtraction) as well as international IgG anticardiolipin units (GPL) or net-GPL. A wide interplate variability of optical densities was found. When results were expressed as GPL, significant differences were only found between Greiner 655061, FALCON ProBIND, and NUNC PolySorp ( P < .05 and P < .001, respectively) whereas differences were not statistically significant if interplate variability was analyzed as net-GPL. Results expressed as categorical variables (ie, positive/negative, according to a GPL cut-off and net-GPL cut-off, obtained with sera from 100 apparently healthy blood donors) showed a good or excellent Cohen's κ coefficient of concordance among plates when positivity was evaluated on net-GPL. Our data strongly suggest that quantification and subtraction of sample blank may improve both interlaboratory agreement and reliability of anticardiolipin assay and minimize false-positive results.

scholarly journals Cholesterol provides nonsacrificial protection of membrane lipids from chemical damage at air–water interface

2018 ◽  
Vol 115 (13) ◽  
pp. 3255-3260 ◽  
Author(s):  
Xinxing Zhang ◽  
Kevin M. Barraza ◽  
J. L. Beauchamp
Keyword(s):  
Lipid Membranes ◽  
Membrane Lipids ◽  
Oh Radicals ◽  
Significant Finding ◽  
Water Interface ◽  
Unsaturated Lipids ◽  
Air Water Interface ◽  
Liquid Ordered ◽  
Ester Linkage

The role of cholesterol in bilayer and monolayer lipid membranes has been of great interest. On the biophysical front, cholesterol significantly increases the order of the lipid packing, lowers the membrane permeability, and maintains membrane fluidity by forming liquid-ordered–phase lipid rafts. However, direct observation of any influence on membrane chemistry related to these cholesterol-induced physical properties has been absent. Here we report that the addition of 30 mol % cholesterol to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (POPG) monolayers at the air–water interface greatly reduces the oxidation and ester linkage cleavage chemistries initiated by potent chemicals such as OH radicals and HCl vapor, respectively. These results shed light on the indispensable chemoprotective function of cholesterol in lipid membranes. Another significant finding is that OH oxidation of unsaturated lipids generates Criegee intermediate, which is an important radical involved in many atmospheric processes.

scholarly journals Colchicine-binding protein of the liver. Its characterization and relation to microtubules.

1975 ◽  
Vol 66 (3) ◽  
pp. 609-620 ◽  
Author(s):  
C Patzelt ◽  
A Singh ◽  
Y L Marchand ◽  
L Orci ◽  
B Jeanrenaud
Keyword(s):  
High Speed ◽  
Specific Binding ◽  
Electrophoretic Analysis ◽  
Binding Activity ◽  
Low Concentrations ◽  
Electrophoretic Behavior ◽  
High Affinity Binding Site ◽  
High Concentrations

Colchicine-binding activity of mouse liver high-speed supernate has been investigated. It has been found to be time and temperature dependent. Two binding activities with different affinities for colchicine seem to be present in this high-speed supernate, of which only the high-affinity binding site (half maximal binding at 5 x 10(-6) M colchicine) can be attributed to microtubular protein by comparison with purified tubulin. Vinblastine interacted with this binding activity by precipitating it when used at high concentrations (2 x 10(-3) M), and by stabilizing it at low concentrations (10(-5) M). Lumicolchicine was found not to compete with colchicine. The colchicine-binding activity was purified from liver and compared with that of microtubular protein from brain. The specific binding activity of the resulting preparation, its electrophoretic behavior, and the electron microscope appearance of the paracrystals obtained upon its precipitation with vinblastine permitted its identification as microtubular protein (tubulin). Electrophoretic analysis of the proteins from liver supernate that were precipitated by vinblastine indicated that this drug was not specific for liver tubulin. Preincubation of liver supernate with 5 mM EGTA resulted in a time-dependent decrease of colchicine-binding activity, which was partly reversed by the addition of Ca++. However, an in vitro formation of microtubules upon lowering the Ca++ concentration could not be detected. Finally, a method was developed enabling that portion of microtubular protein which was present as free tubulin to be measured and to be compared with the total amount of this protein in the tissue. This procedure permitted demonstration of the fact that, under normal conditions, only about 40% of the tubulin of the liver was assemled as microtubules. It is suggested that, in the liver, rapid polymerization and depolymerization of microtubules occur and may be an important facet of the functional role of the microtubular system.

Role of Fe(III) in Fe(II)citrate-mediated peroxidation of mitochondrial membrane lipids

1999 ◽  
pp. 163-168
Author(s):  
Roger F. Castilho ◽  
André R. Meinicke ◽  
Anibal E. Vercesi ◽  
Marcelo Hermes-Lima
Keyword(s):  
Mitochondrial Membrane ◽  
Membrane Lipids
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