The Experts below are selected from a list of 6120 Experts worldwide ranked by ideXlab platform
Frances Separovic - One of the best experts on this subject based on the ideXlab platform.
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Anionic Phospholipid interactions of the prion protein n terminus are minimally perturbing and not driven solely by the octapeptide repeat domain
Journal of Biological Chemistry, 2010Co-Authors: Martin Boland, Frances Separovic, Claire R Hatty, Andrew F Hill, Kevin J Barnham, Cathryn L Haigh, Michael N G James, Colin L Masters, Steven J CollinsAbstract:Although the N terminus of the prion protein (PrPC) has been shown to directly associate with lipid membranes, the precise determinants, biophysical basis, and functional implications of such binding, particularly in relation to endogenously occurring fragments, are unresolved. To better understand these issues, we studied a range of synthetic peptides: specifically those equating to the N1 (residues 23–110) and N2 (23–89) fragments derived from constitutive processing of PrPC and including those representing arbitrarily defined component domains of the N terminus of mouse prion protein. Utilizing more physiologically relevant large unilamellar vesicles, fluorescence studies at synaptosomal pH (7.4) showed absent binding of all peptides to lipids containing the zwitterionic headgroup phosphatidylcholine and mixtures containing the Anionic headgroups phosphatidylglycerol or phosphatidylserine. At pH 5, typical of early endosomes, quartz crystal microbalance with dissipation showed the highest affinity binding occurred with N1 and N2, selective for Anionic lipid species. Of particular note, the absence of binding by individual peptides representing component domains underscored the importance of the combination of the octapeptide repeat and the N-terminal polybasic regions for effective membrane interaction. In addition, using quartz crystal microbalance with dissipation and solid-state NMR, we characterized for the first time that both N1 and N2 deeply insert into the lipid bilayer with minimal disruption. Potential functional implications related to cellular stress responses are discussed.
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effect of antimicrobial peptides from australian tree frogs on Anionic Phospholipid membranes
Biophysical Journal, 2009Co-Authors: Frances Separovic, Johh D Gehman, John H Bowie, Marieisabel AguilarAbstract:Skin secretions of numerous Australian tree frogs contain antimicrobial peptides that form part of the host defense mechanism against bacterial infection. The mode of action of these antibiotics is thought to be lysis of infectious organisms via cell membrane disruption, on the basis of vesicle-encapsulated dye leakage data [Ambroggio et al. (2005) Biophys. J. 89, 1874−1881]. A detailed understanding of the interaction of these peptides with bacterial membranes at a molecular level, however, is critical to their development as novel antibacterial therapeutics. We focus on four of these peptides, aurein 1.2, citropin 1.1, maculatin 1.1, and caerin 1.1, which exist as random coil in aqueous solution but have α-helical secondary structure in membrane mimetic environments. In our earlier solid-state NMR studies, only neutral bilayers of the zwitterionic Phospholipid dimyristoylphosphatidylcholine (DMPC) were used. Deuterated DMPC (d54-DMPC) was used to probe the effect of the peptides on the order of the lipi...
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effect of antimicrobial peptides from australian tree frogs on Anionic Phospholipid membranes
Biochemistry, 2008Co-Authors: Johh D Gehman, Kristopher Norman Hall, Martin Boland, Tara L Pukala, John H Bowie, Marieisabel Aguilar, Frances SeparovicAbstract:Skin secretions of numerous Australian tree frogs contain antimicrobial peptides that form part of the host defense mechanism against bacterial infection. The mode of action of these antibiotics is thought to be lysis of infectious organisms via cell membrane disruption, on the basis of vesicle-encapsulated dye leakage data [Ambroggio et al. (2005) Biophys. J. 89, 1874-1881]. A detailed understanding of the interaction of these peptides with bacterial membranes at a molecular level, however, is critical to their development as novel antibacterial therapeutics. We focus on four of these peptides, aurein 1.2, citropin 1.1, maculatin 1.1, and caerin 1.1, which exist as random coil in aqueous solution but have α-helical secondary structure in membrane mimetic environments. In our earlier solid-state NMR studies, only neutral bilayers of the zwitterionic Phospholipid dimyristoylphosphatidylcholine (DMPC) were used. Deuterated DMPC (d 54 -DMPC) was used to probe the effect of the peptides on the order of the lipid acyl chains and dynamics of the Phospholipid headgroups by deuterium and 31 P NMR, respectively. In this report we demonstrate several important differences when Anionic Phospholipid is included in model membranes. Peptide-membrane interactions were characterized using surface plasmon resonance (SPR) spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy. Changes in Phospholipid motions and membrane binding information provided additional insight into the action of these antimicrobial peptides. While this set of peptides has significant C- and N-terminal sequence homology, they vary in their mode of membrane interaction. The longer peptides caerin and maculatin exhibited properties that were consistent with transmembrane insertion while citropin and aurein demonstrated membrane disruptive mechanisms. Moreover, aurein was unique with greater perturbation of neutral versus Anionic membranes. The results are consistent with a surface interaction for aurein 1.2 and pore formation rather than membrane lysis by the longer peptides.
Miriam L Greenberg - One of the best experts on this subject based on the ideXlab platform.
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Deficiency in mitochondrial Anionic Phospholipid synthesis impairs cell wall biogenesis.
Biochemical Society transactions, 2020Co-Authors: Q Zhong, Miriam L GreenbergAbstract:Cardiolipin (CL) is the signature lipid of the mitochondrial membrane and plays a key role in mitochondrial physiology and cell viability. The importance of CL is underscored by the finding that the severe genetic disorder Barth syndrome results from defective CL composition and acylation. Disruption of PGS1, which encodes the enzyme that catalyses the committed step of CL synthesis, results in loss of the mitochondrial Anionic Phospholipids phosphatidylglycerol and CL. The pgs1Delta mutant exhibits severe growth defects at 37 degrees C. To understand the essential functions of mitochondrial Anionic lipids at elevated temperatures, we isolated suppressors of pgs1Delta that grew at 37 degrees C. The present review summarizes our analysis of suppression of pgs1Delta growth defects by a mutant that has a loss-of-function mutation in KRE5, a gene involved in cell wall biogenesis.
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deficiency in mitochondrial Anionic Phospholipid synthesis impairs cell wall biogenesis
Biochemical Society Transactions, 2005Co-Authors: Q Zhong, Miriam L GreenbergAbstract:Cardiolipin (CL) is the signature lipid of the mitochondrial membrane and plays a key role in mitochondrial physiology and cell viability. The importance of CL is underscored by the finding that the severe genetic disorder Barth syndrome results from defective CL composition and acylation. Disruption of PGS1 ,w hich encodes the enzyme that catalyses the committed step of CL synthesis, results in loss of the mitochondrial Anionic Phospholipids phosphatidylglycerol and CL. The pgs1∆ mutant exhibits severe growth defects at 37 ◦ C. To understand the essential functions of mitochondrial Anionic lipids at elevated temperatures, we isolated suppressors of pgs1∆ that grew at 37 ◦ C. The present review summarizes our analysis of suppression of pgs1∆ growth defects by a mutant that has a loss-of-function mutation in KRE5, a gene involved in cell
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Deficiency in mitochondrial Anionic Phospholipid synthesis impairs cell wall biogenesis
Biochemical Society Transactions, 2005Co-Authors: Q Zhong, Miriam L GreenbergAbstract:Cardiolipin (CL) is the signature lipid of the mitochondrial membrane and plays a key role in mitochondrial physiology and cell viability. The importance of CL is underscored by the finding that the severe genetic disorder Barth syndrome results from defective CL composition and acylation. Disruption of PGS1, which encodes the enzyme that catalyses the committed step of CL synthesis, results in loss of the mitochondrial Anionic Phospholipids phosphatidylglycerol and CL. The pgs1Δ mutant exhibits severe growth defects at 37°C. To understand the essential functions of mitochondrial Anionic lipids at elevated temperatures, we isolated suppressors of pgs1Δ that grew at 37°C. The present review summarizes our analysis of suppression of pgs1Δ growth defects by a mutant that has a loss-of-function mutation in KRE5, a gene involved in cell wall biogenesis.
Jose Requejoisidro - One of the best experts on this subject based on the ideXlab platform.
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a complex interplay of Anionic Phospholipid binding regulates 3 phosphoinositide dependent kinase 1 homodimer activation
Scientific Reports, 2019Co-Authors: Gloria De Las Herasmartinez, Veronique Calleja, Remy Bailly, Jean Dessolin, Jose Requejoisidro, Banafshe LarijaniAbstract:3′-Phosphoinositide-dependent-Kinase-1 (PDK1) is a master regulator whereby its PI3-kinase-dependent dysregulation in human pathologies is well documented. Understanding the direct role for PtdIns(3,4,5)P3 and other Anionic Phospholipids in the regulation of PDK1 conformational dynamics and its downstream activation remains incomplete. Using advanced quantitative-time-resolved imaging (Fluorescence Lifetime Imaging and Fluorescence Correlation Spectroscopy) and molecular modelling, we show an interplay of antagonistic binding effects of PtdIns(3,4,5)P3 and other Anionic Phospholipids, regulating activated PDK1 homodimers. We demonstrate that phosphatidylserine maintains PDK1 in an inactive conformation. The dysregulation of the PI3K pathway affects the spatio-temporal and conformational dynamics of PDK1 and the activation of its downstream substrates. We have established a new Anionic-Phospholipid-dependent model for PDK1 regulation, depicting the conformational dynamics of multiple homodimer states. We show that the dysregulation of the PI3K pathway perturbs equilibrium between the PDK1 homodimer conformations. Our findings provide a role for the PtdSer binding site and its previously unrewarding role in PDK1 downregulation, suggesting a possible therapeutic strategy where the constitutively active dimer conformer of PDK1 may be rendered inactive by small molecules that drive it to its PtdSer-bound conformer.
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a complex interplay of Anionic Phospholipid binding regulates 3 phosphoinositide dependent kinase 1 homodimer activation
bioRxiv, 2019Co-Authors: G De Las Heras, Veronique Calleja, Remy Bailly, Jean Dessolin, Jose Requejoisidro, Banafshe LarijaniAbstract:3-Phosphoinositide-dependent-Kinase-1 is a master regulator whereby its PI3- kinase-dependent dysregulation in human pathologies is well documented. Understanding the direct role for PtdIns(3,4,5)P3 and other Anionic Phospholipids in the regulation of PDK1 conformational dynamics and its downstream activation remains incomplete. Using advanced quantitative-time-resolved imaging, FCS and molecular modelling, we show an interplay of antagonistic binding effects of PtdIns(3,4,5)P3 and other Anionic Phospholipids, regulating activated PDK1 homodimers. We demonstrate that phosphatidylserine maintains PDK1 in an inactive conformation. The dysregulation of the PI3K pathway affects the spatio-temporal and conformational dynamics of PDK1 and the activation of its downstream substrates. We establish an Anionic-Phospholipid-dependent model for PDK1 regulation, depicting the conformational dynamics of multiple homodimer states. The dysregulation of the PI3K pathway perturbs equilibrium between the PDK1 homodimer conformations. Our findings indicate that the alteration of specific basic residues of PDK1-PH domain leads to its constitutive activation, potential significance in different types of carcinomas.
Lia Q Amaral - One of the best experts on this subject based on the ideXlab platform.
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pore model in the melting regime of a lyotropic biomembrane with an Anionic Phospholipid
Langmuir, 2016Co-Authors: Francesco Spinozzi, Lia Q AmaralAbstract:Aqueous dispersions of the Anionic Phospholipid dimyristoyl phosphatidyl glycerol (DMPG) exhibit an unusual “melting regime”, at the phase transition between the ordered (gel) and the disordered (fluid liquid crystal) state of hydrocarbon chains, depending on the ionic strength and DMPG concentration, previously attributed to the pore formation. Dispersions with 150 mM DMPG present a lamellar phase above 23 °C, within the melting regime. In this study, we present a detailed pore model for the analysis of small-angle X-ray scattering (SAXS) results and their variation with temperature, focused on the surface fractions of pores in the bilayers. Large and small toroidal pores are necessary to explain the SAXS results. Pores have DMPG in the fluid conformation, whereas the flat region of the bilayer has DMPG molecules in fluid and in gel conformations. A particular strategy was developed to estimate the charges due to the localization of mobile ions in the system, which is based on the calculation of electron...
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new lamellar phase with pores in the chain melting regime of an Anionic Phospholipid dispersion
Journal of Physics: Conference Series, 2010Co-Authors: Francesco Spinozzi, Lydia Paccamiccio, Paolo Mariani, Lia Q AmaralAbstract:The Anionic Phospholipid DMPG (dimyristoyl phosphatidylglycerol) may exhibit in water, instead of a unique melting transition of the hydrocarbon chains, a "melting regime" for pH values above 5, where the phosphate groups are deprotonated, and for low ionic strength, where charge screening is weak. The chain-melting process of DMPG starts at (onset of the melting regime at ~ 20°C), but the complete fluid phase exists only above (offset of the melting regime at ~ 30°C). In a recent paper we developed a SAXS model for a bilayer with pores to explain SAXS results obtained for concentrations up to 70 mM DMPG (F. Spinozzi, L. Paccamiccio, P. Mariani, and L. Q. Amaral, Langmuir, in print, 2010). A new lamellar phase with pores, starting 3°C above and existing up to 4°C above , was also identified at the higher investigated DMPG concentrations (up to 300 mM DMPG). In this paper we focus in more detail the SAXS curves obtained in the concentration interval 70-300 mM DMPG. The slope of the scattering profile in the very small q range, as well as the anomalous increase in the intensity of the bilayer band centered around 0.12 A−1 after , have been in particular analyzed. By using a model of water-penetrated bilayers, the volume fractions of DMPG and water molecules inside the bilayer was derived as a function of temperature.
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melting regime of the Anionic Phospholipid dmpg new lamellar phase and porous bilayer model
Langmuir, 2010Co-Authors: Francesco Spinozzi, Lydia Paccamiccio, Paolo Mariani, Lia Q AmaralAbstract:Aqueous dispersions of the Anionic Phospholipid dimyristoyl phosphatidylglycerol (DMPG) at pH above the apparent pK of DMPG and concentrations in the interval 70−300 mM have been investigated by small (SAXS) and wide-angle X-ray scattering, differential scanning calorimetry, and polarized optical microscopy. The order−disorder transition of the hydrocarbon chains occurs along an interval of about 10 °C (between Tmon ∼ 20 °C and Tmoff ∼ 30 °C). Such melting regime was previously characterized at lower concentrations, up to 70 mM DMPG, when sample transparency was correlated with the presence of pores across the bilayer. At higher concentrations considered here, the melting regime persists but is not transparent. Defined SAXS peaks appear and a new lamellar phase Lp with pores is proposed to exist above 70 mM DMPG, starting at ∼23 °C (∼3 °C above Tmon) and losing correlation after Tmoff. A new model for describing the X-ray scattering of bilayers with pores, presented here, is able to explain the broad band...
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extensive bilayer perforation coupled with the phase transition region of an Anionic Phospholipid
Langmuir, 2009Co-Authors: Karin A Riske, Lia Q Amaral, Maria Teresa Moura LamyAbstract:At low ionic strength dimyristoylphosphatidylglycerol (DMPG) exhibits a broad phase transition region characterized by several superimposed calorimetric peaks. Peculiar properties, such as sample transparency, are observed only in the transition region. In this work we use differential scanning calorimetry (DSC), turbidity, and optical microscopy to study the narrowing of the transition region with the increase of ionic strength (0-500 mM NaCl). Upon addition of salt, the temperature extension of the transition region is reduced, and the number of calorimetric peaks decreases until a single cooperative event at T(m) = 23 degrees C is observed in the presence of 500 mM NaCl. The transition region is always coupled with a decrease in turbidity, but a transparent region is detected within the melting process only in the presence of up to 20 mM NaCl. The vanishing of the transparent region is associated with one of the calorimetric peaks. Optical microscopy of giant vesicles shows that bilayers first rupture when the transition region is reached and subsequently lose optical contrast. Fluorescence microscopy reveals a blurry and undefined image in the transparent region, suggesting a different lipid self-assembly. Overall sample turbidity can be directly related to the bilayer optical contrast. Our observations are discussed in terms of the bilayer being perforated along the transition region. In the narrower temperature interval of the transparent region, dependent on the ionic strength, the perforation is extensive and the bilayer completely loses the optical contrast.
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mesoscopic structure in the chain melting regime of Anionic Phospholipid vesicles dmpg
Biophysical Journal, 2004Co-Authors: Karin A Riske, Lia Q Amaral, Hansgunther Dobereiner, Maria Teresa Moura LamyAbstract:Abstract In a range of low ionic strength, aqueous dispersions of the Anionic Phospholipid DMPG (dimyristoylphosphatidylglycerol) have a transparent intermediate phase (IP, between T m on ≅ 20 ∘ C and T m off ≅ 30 ∘ C ) between the turbid gel and fluid membrane phases, evidenced in turbidity data. Small angle x-ray scattering results on DMPG dispersions show that, besides the bilayer peak present in all phases, a peak corresponding to a mesoscopic structure at ∼400A is detected only in IP. The dependence of this peak position on DMPG concentration suggests a correlation in the bilayer plane, consistent with the stability of vesicles in IP. Moreover, observation of giant DMPG vesicles with phase contrast light microscopy show that vesicles "disappear" upon cooling below T m off and "reappear" after reheating. This further proves that although vesicles cannot be visualized in IP, their overall structure is maintained. We propose that the IP in the melting regime corresponds to unilamellar vesicles with perforations, a model which is consistent with all described experimental observations. Furthermore, the opening of pores across the membrane tuned by ionic strength, temperature, and lipid composition is likely to have biological relevance and could be used in applications for controlled release from nanocompartments.
Marieisabel Aguilar - One of the best experts on this subject based on the ideXlab platform.
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effect of antimicrobial peptides from australian tree frogs on Anionic Phospholipid membranes
Biophysical Journal, 2009Co-Authors: Frances Separovic, Johh D Gehman, John H Bowie, Marieisabel AguilarAbstract:Skin secretions of numerous Australian tree frogs contain antimicrobial peptides that form part of the host defense mechanism against bacterial infection. The mode of action of these antibiotics is thought to be lysis of infectious organisms via cell membrane disruption, on the basis of vesicle-encapsulated dye leakage data [Ambroggio et al. (2005) Biophys. J. 89, 1874−1881]. A detailed understanding of the interaction of these peptides with bacterial membranes at a molecular level, however, is critical to their development as novel antibacterial therapeutics. We focus on four of these peptides, aurein 1.2, citropin 1.1, maculatin 1.1, and caerin 1.1, which exist as random coil in aqueous solution but have α-helical secondary structure in membrane mimetic environments. In our earlier solid-state NMR studies, only neutral bilayers of the zwitterionic Phospholipid dimyristoylphosphatidylcholine (DMPC) were used. Deuterated DMPC (d54-DMPC) was used to probe the effect of the peptides on the order of the lipi...
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effect of antimicrobial peptides from australian tree frogs on Anionic Phospholipid membranes
Biochemistry, 2008Co-Authors: Johh D Gehman, Kristopher Norman Hall, Martin Boland, Tara L Pukala, John H Bowie, Marieisabel Aguilar, Frances SeparovicAbstract:Skin secretions of numerous Australian tree frogs contain antimicrobial peptides that form part of the host defense mechanism against bacterial infection. The mode of action of these antibiotics is thought to be lysis of infectious organisms via cell membrane disruption, on the basis of vesicle-encapsulated dye leakage data [Ambroggio et al. (2005) Biophys. J. 89, 1874-1881]. A detailed understanding of the interaction of these peptides with bacterial membranes at a molecular level, however, is critical to their development as novel antibacterial therapeutics. We focus on four of these peptides, aurein 1.2, citropin 1.1, maculatin 1.1, and caerin 1.1, which exist as random coil in aqueous solution but have α-helical secondary structure in membrane mimetic environments. In our earlier solid-state NMR studies, only neutral bilayers of the zwitterionic Phospholipid dimyristoylphosphatidylcholine (DMPC) were used. Deuterated DMPC (d 54 -DMPC) was used to probe the effect of the peptides on the order of the lipid acyl chains and dynamics of the Phospholipid headgroups by deuterium and 31 P NMR, respectively. In this report we demonstrate several important differences when Anionic Phospholipid is included in model membranes. Peptide-membrane interactions were characterized using surface plasmon resonance (SPR) spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy. Changes in Phospholipid motions and membrane binding information provided additional insight into the action of these antimicrobial peptides. While this set of peptides has significant C- and N-terminal sequence homology, they vary in their mode of membrane interaction. The longer peptides caerin and maculatin exhibited properties that were consistent with transmembrane insertion while citropin and aurein demonstrated membrane disruptive mechanisms. Moreover, aurein was unique with greater perturbation of neutral versus Anionic membranes. The results are consistent with a surface interaction for aurein 1.2 and pore formation rather than membrane lysis by the longer peptides.
