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Alan R Tall - One of the best experts on this subject based on the ideXlab platform.
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the role of plasma Lipid Transfer Proteins in lipoprotein metabolism and atherogenesis
Journal of Lipid Research, 2009Co-Authors: David Masson, Xiancheng Jiang, Laurent Lagrost, Alan R TallAbstract:The plasma Lipid Transfer Proteins promote the exchange of neutral Lipids and phosphoLipids between the plasma lipoProteins. Cholesteryl ester Transfer protein (CETP) facilitates the removal of cholesteryl esters from HDL and thus reduces HDL levels, while phosphoLipid Transfer protein (PLTP) promotes the Transfer of phosphoLipids from triglyceride-rich lipoProteins into HDL and increases HDL levels. Studies in transgenic mouse models and in humans with rare genetic deficiencies (CETP) or common genetic variants (CETP and PLTP) highlight the central role of these molecules in regulating HDL levels. Human CETP deficiency is associated with dramatic elevations of HDL cholesterol and apolipoprotein A-I levels, while PLTP variants with increased expression are associated with higher HDL levels. A recent meta-analysis suggests that common CETP alleles causing reduced CETP and increased HDL levels are associated with reduced coronary heart disease. The failure of a clinical trial with the CETP inhibitor torcetrapib may have been related in part to off-target toxicity. Ongoing phase 3 clinical trials with other CETP inhibitors may help to clarify if this strategy can ultimately be successful in the treatment of atherosclerosis.
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receptors and Lipid Transfer Proteins in hdl metabolism
Annals of the New York Academy of Sciences, 2006Co-Authors: David L Silver, T Arai, Xiancheng Jiang, Can Bruce, Alan R TallAbstract:It is believed that HDL exerts its anti-atherogenic effects through the process of delivering cholesterol from peripheral tissues back to the liver for removal from the body (i.e., reverse cholesterol transport). The metabolic life cycle of HDL Lipid and apolipoProteins during reverse cholesterol transport involves both its modification in plasma by Lipid Transfer Proteins and the clearance from plasma of HDL Lipid and protein mediated by hepatic cell surface Proteins. We review recent work from our laboratory that focuses on specific metabolic steps in reverse cholesterol transport and the results of altering these steps on plasma HDL levels and atherosclerosis. Recently, SR-BI was shown to be an authentic HDL receptor mediating the selective uptake of HDL Lipids into cells without degradation of HDL Proteins. We discuss the evidence for additional receptor activity mediating HDL protein catabolism in the liver from studies in obese (ob/ob) mice, which have markedly increased HDL due to a defect in hepatic catabolism of apoA-I and apoA-II. In addition, we review recent findings that phosphoLipid Transfer protein deficiency in mice results in markedly reduced HDL levels. Lastly, we highlight our findings that overexpression of SR-BI in LDL receptor-deficient mice results in decreased atherosclerosis.
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1999 george lyman duff memorial lecture Lipid Transfer Proteins hdl metabolism and atherogenesis
Arteriosclerosis Thrombosis and Vascular Biology, 2000Co-Authors: Alan R Tall, Xiancheng Jiang, Yi Luo, David L SilverAbstract:Plasma high density lipoprotein (HDL) levels show an inverse relationship to atherogenesis, in part reflecting the role of HDL in mediating reverse cholesterol transport. The Transfer of HDL cholesterol to the liver involves 3 catabolic pathways: the indirect, cholesteryl ester Transfer protein (CETP)-mediated pathway, the selective uptake (scavenger receptor BI) pathway, and a particulate HDL uptake pathway. The functions of the Lipid Transfer Proteins (CETP and phosphoLipid Transfer protein) in HDL metabolism have been elucidated by genetic approaches in humans and mice. Human CETP deficiency is associated with increased HDL levels but appears to increase coronary artery disease risk. PhosphoLipid Transfer protein deficiency, produced by gene knockout in mice, results in decreased HDL levels, reflecting decreased Transfer of phosphoLipids from triglyceride-rich lipoProteins into HDL. Obese (ob/ob) mice have markedly increased HDL levels and represent an interesting model of defective HDL catabolism in the liver. In hepatocytes of wild-type mice, there is extensive uptake and resecretion of HDL and selective uptake of cholesteryl ester from HDL during recycling. In ob/ob mice, these processes are defective, suggesting that HDL recycling plays an important role in holo-HDL catabolism, selective uptake, and the determination of plasma HDL levels.
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7. Lipid Transfer Proteins and receptors in HDL metabolism
Atherosclerosis, 1999Co-Authors: Alan R Tall, X.c. Jiang, T Arai, N Wang, David SilverAbstract:Plasma high density lipoprotein (HDL) levels are determined bath by intravascular metabolism and by clearance pathways. Recent evidence indicates that plasma Lipid Transfer Proteins play a major role in the intravascular metabolism of HDL, while HDL receptors in tissues are important in HDL catabolism. The role of the plasma Lipid Transfer Proteins, cholesteryl ester Transfer protein (CETP) and phosphoLipid Transfer protein (PLTP), have been elucidated by genetic deficiency states in humans or mice, or by overexpression experiments in mice. Human CETP deficiency results in increased HDL levels, but also increased coronary heart disease, suggesting an antiatherogenic function of CETP related to its role in reverse cholesterol transport. PLTP knock-out mice have absent plasma phosphoLipid Transfer activity and markedly reduced HDL cholesterol and apoA-I levels, demonstrating the crucial role that the Transfer of surface phosphoLipid of triglyceride-rich lipoProteins plays in the maintenance of HDL levels. Scavenger receptor BI has recently emerged as an authentic HDL receptor mediating the selective uptake of HDL CE in liver and steroidogenic tissue. Overexpression of SR-BI in transgenic mice results in low HDL levels, and also decreases VLDL and LDL cholesterol and apoB levels, and reduces atherosclerosis in response to a high cholesterol/bile salt diet. Knock-out of SR-BI results in increased HDL levels due to decreased selective uptake in the liver, but the catabolism of HDL Proteins is unaltered. Recent studies in obese (ob/ob) mice show a catabolic defect of HDL protein in the liver and suggest a leptin-regulated liver catabolic process for apoA-I and apoA-II. Thus, while CETP, PLTP and SR-BI are important in the turnover of HDL Lipids, it appears that distinct receptors are involved in the catabolism of HDL Proteins.
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Plasma Lipid Transfer Proteins
Annual review of biochemistry, 1995Co-Authors: Alan R TallAbstract:The plasma Lipid Transfer Proteins mediate the Transfer and exchange of phosphoLipids and neutral Lipids between the plasma lipoProteins. The cholesteryl ester Transfer protein (CETP) and the phosphoLipid Transfer protein (PLTP) are members of the Lipid Transfer/lipopolysaccharide binding gene family. The CETP contains binding sites for cholesteryl ester and triglycerides and probably acts by a carrier-mediated mechanism. The CETP mediates catabolism of HDL cholesteryl esters, with secondary decreases in HDL size and protein content. The CETP plays a central role in reverse cholesterol transport i.e. the centripetal movement of cholesterol from the periphery back to the liver. CETP gene expression is upregulated in response to increased dietary cholesterol or endogenous hypercholesterolemia. Although CETP reduces HDL levels, its role in reverse cholesterol transport suggests a dominant anti-atherogenic action in vivo.
Sima Lev - One of the best experts on this subject based on the ideXlab platform.
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Lipid Transfer Proteins and Membrane Contact Sites in Human Cancer.
Frontiers in cell and developmental biology, 2020Co-Authors: Diego Peretti, Sohui Kim, Roberta Tufi, Sima LevAbstract:Lipid-Transfer Proteins (LTPs) were initially discovered as cytosolic factors that facilitate Lipid transport between membrane bilayers in vitro. Since then, many LTPs have been isolated from bacteria, plants, yeast, and mammals, and extensively studied in cell-free systems and intact cells. A major advance in the LTP field was associated with the discovery of intracellular membrane contact sites (MCSs), small cytosolic gaps between the endoplasmic reticulum (ER) and other cellular membranes, which accelerate Lipid Transfer by LTPs. As LTPs modulate the distribution of Lipids within cellular membranes, and many Lipid species function as second messengers in key signaling pathways that control cell survival, proliferation, and migration, LTPs have been implicated in cancer-associated signal transduction cascades. Increasing evidence suggests that LTPs play an important role in cancer progression and metastasis. This review describes how different LTPs as well as MCSs can contribute to cell transformation and malignant phenotype, and discusses how "aberrant" MCSs are associated with tumorigenesis in human.
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Non-vesicular Lipid transport by Lipid-Transfer Proteins and beyond
Nature Reviews Molecular Cell Biology, 2010Co-Authors: Sima LevAbstract:The movement of Lipids within and between intracellular membranes is mediated by different Lipid transport mechanisms and is crucial for maintaining the identities of different cellular organelles. Non-vesicular Lipid transport has a crucial role in intracellular Lipid trafficking and distribution, but its underlying mechanisms remain unclear. Lipid-Transfer Proteins (LTPs), which regulate diverse Lipid-mediated cellular processes and accelerate vectorial transport of Lipid monomers between membranes in vitro , could potentially mediate non-vesicular intracellular Lipid trafficking. Understanding the mechanisms by which Lipids are transported and distributed between cellular membranes, and elucidating the role of LTPs in intracellular Lipid transport and homeostasis, are currently subjects of intensive study. Non-vesicular Lipid transport between intracellular membranes can be mediated by spontaneous Lipid Transfer or Lipid-Transfer Proteins (LTPs) and is crucial for maintaining the identities of different cellular membranes. Current studies focus on further understanding the mechanisms of non-vesicular Lipid transport and elucidating the role of LTPs in intact cells. Non-vesicular Lipid transport plays a crucial part in intracellular Lipid trafficking and can be mediated by spontaneous Lipid transport or by Lipid-Transfer Proteins (LTPs). LTPs markedly facilitate (by several orders of magnitude) the transport of Lipids between membranes in vitro . Non-vesicular Lipid transport is thought to be greatly enhanced at membrane contact sites; small cytosolic gaps between the endoplasmic reticulum membrane and virtually all other cellular organelles. LTPs do not mediate a simple vectorial Lipid transport from one membrane to another. Rather, they facilitate Lipid transport between membranes according to their membrane environment. LTPs use their Lipid-Transfer activity to regulate various cellular processes, including vesicular trafficking, signal transduction and Lipid metabolism.
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Non-vesicular Lipid transport by Lipid-Transfer Proteins and beyond
Nature Reviews Molecular Cell Biology, 2010Co-Authors: Sima LevAbstract:The movement of Lipids within and between intracellular membranes is mediated by different Lipid transport mechanisms and is crucial for maintaining the identities of different cellular organelles. Non-vesicular Lipid transport has a crucial role in intracellular Lipid trafficking and distribution, but its underlying mechanisms remain unclear. Lipid-Transfer Proteins (LTPs), which regulate diverse Lipid-mediated cellular processes and accelerate vectorial transport of Lipid monomers between membranes in vitro, could potentially mediate non-vesicular intracellular Lipid trafficking. Understanding the mechanisms by which Lipids are transported and distributed between cellular membranes, and elucidating the role of LTPs in intracellular Lipid transport and homeostasis, are currently subjects of intensive study.
Louise H. Wong - One of the best experts on this subject based on the ideXlab platform.
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Lipid Transfer Proteins: the Lipid commute via shuttles, bridges and tubes
Nature Reviews Molecular Cell Biology, 2019Co-Authors: Louise H. Wong, Alberto T. Gatta, Tim P. LevineAbstract:The distribution of Lipids largely depends on their non-vesicular transport by Lipid Transfer Proteins (LTPs). Recent progress in understanding the mechanisms of LTPs, including the appreciation of their widespread activity at membrane contact sites, has provided novel insights into the regulation of Lipid trafficking and how it impacts pathophysiology. Lipids are distributed in a highly heterogeneous fashion in different cellular membranes. Only a minority of Lipids achieve their final intracellular distribution through transport by vesicles. Instead, the bulk of Lipid traffic is mediated by a large group of Lipid Transfer Proteins (LTPs), which move small numbers of Lipids at a time using hydrophobic cavities that stabilize Lipid molecules outside membranes. Although the first LTPs were discovered almost 50 years ago, most progress in understanding these Proteins has been made in the past few years, leading to considerable temporal and spatial refinement of our understanding of the function of these Lipid transporters. The number of known LTPs has increased, with exciting discoveries of their multimeric assembly. Structural studies of LTPs have progressed from static crystal structures to dynamic structural approaches that show how conformational changes contribute to Lipid handling at a sub-millisecond timescale. A major development has been the finding that many intracellular LTPs localize to two organelles at the same time, forming a shuttle, bridge or tube that links donor and acceptor compartments. The understanding of how different Lipids achieve their final destination at the molecular level allows a better explanation of the range of defects that occur in diseases associated with Lipid transport and distribution, opening up the possibility of developing therapies that specifically target Lipid Transfer.
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Lipid Transfer Proteins the Lipid commute via shuttles bridges and tubes
Nature Reviews Molecular Cell Biology, 2019Co-Authors: Louise H. Wong, Alberto T. Gatta, Tim P. LevineAbstract:Lipids are distributed in a highly heterogeneous fashion in different cellular membranes. Only a minority of Lipids achieve their final intracellular distribution through transport by vesicles. Instead, the bulk of Lipid traffic is mediated by a large group of Lipid Transfer Proteins (LTPs), which move small numbers of Lipids at a time using hydrophobic cavities that stabilize Lipid molecules outside membranes. Although the first LTPs were discovered almost 50 years ago, most progress in understanding these Proteins has been made in the past few years, leading to considerable temporal and spatial refinement of our understanding of the function of these Lipid transporters. The number of known LTPs has increased, with exciting discoveries of their multimeric assembly. Structural studies of LTPs have progressed from static crystal structures to dynamic structural approaches that show how conformational changes contribute to Lipid handling at a sub-millisecond timescale. A major development has been the finding that many intracellular LTPs localize to two organelles at the same time, forming a shuttle, bridge or tube that links donor and acceptor compartments. The understanding of how different Lipids achieve their final destination at the molecular level allows a better explanation of the range of defects that occur in diseases associated with Lipid transport and distribution, opening up the possibility of developing therapies that specifically target Lipid Transfer.
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Advances on the Transfer of Lipids by Lipid Transfer Proteins
Trends in biochemical sciences, 2017Co-Authors: Louise H. Wong, Alenka Čopič, Timothy P. LevineAbstract:Transfer of Lipid across the cytoplasm is an essential process for intracellular Lipid traffic. Lipid Transfer Proteins (LTPs) are defined by highly controlled in vitro experiments. The functional relevance of these is supported by evidence for the same reactions inside cells. Major advances in the LTP field have come from structural bioinformatics identifying new LTPs, and from the development of countercurrent models for LTPs. However, the ultimate aim is to unite in vitro and in vivo data, and this is where much progress remains to be made. Even where in vitro and in vivo experiments align, rates of Transfer tend not to match. Here we set out some of the advances that might test how LTPs work.
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Lipid Transfer Proteins do their thing anchored at membrane contact sites… but what is their thing?
Biochemical Society transactions, 2016Co-Authors: Louise H. Wong, Timothy P. LevineAbstract:Membrane contact sites are structures where two organelles come close together to regulate flow of material and information between them. One type of inter-organelle communication is Lipid exchange, which must occur for membrane maintenance and in response to environmental and cellular stimuli. Soluble Lipid Transfer Proteins have been extensively studied, but additional families of Transfer Proteins have been identified that are anchored into membranes by transmembrane helices so that they cannot diffuse through the cytosol to deliver Lipids. If such Proteins target membrane contact sites they may be major players in Lipid metabolism. The eukaryotic family of so-called Lipid Transfer Proteins Anchored at Membrane contact sites (LAMs) all contain both a sterol-specific Lipid Transfer domain in the StARkin superfamily (related to StART/Bet_v1), and one or more transmembrane helices anchoring them in the endoplasmic reticulum (ER), making them interesting subjects for study in relation to sterol metabolism. They target a variety of membrane contact sites, including newly described contacts between organelles that were already known to make contact by other means. Lam1-4p target punctate ER-plasma membrane contacts. Lam5p and Lam6p target multiple contacts including a new category: vacuolar non-NVJ cytoplasmic ER (VancE) contacts. These developments confirm previous observations on tubular Lipid-binding Proteins (TULIPs) that established the importance of membrane anchored Proteins for Lipid traffic. However, the question remaining to be solved is the most difficult of all: are LAMs transporters, or alternately are they regulators that affect traffic more indirectly?
Tim P. Levine - One of the best experts on this subject based on the ideXlab platform.
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tmem106b in humans and vac7 and tag1 in yeast are predicted to be Lipid Transfer Proteins
bioRxiv, 2021Co-Authors: Tim P. LevineAbstract:TMEM106B is an integral membrane protein of late endosomes and lysosomes involved in neuronal function, its over-expression being associated with familial frontotemporal lobar degeneration, and under-expression linked to hypomyelination. It has also been identified in multiple screens for host Proteins required for productive SARS-CoV2 infection. Because standard approaches to understand TMEM106B at the sequence level find no homology to other Proteins, it has remained a protein of unknown function. Here, the standard tool PSI-BLAST was used in a non-standard way to show that the lumenal portion of TMEM106B is a member of the LEA-2 domain superfamily. The non-standard tools (HMMER, HHpred and trRosetta) extended this to predict two yeast LEA-2 Proteins in the lumenal domains of the degradative vacuole, equivalent to the lysosome: one in Vac7, a regulator of PI(3,5)P2 production, and three in Tag1 which signals to terminate autophagy. Further analysis of previously unreported LEA-2 structures indicated that LEA-2 domains have a long, conserved Lipid binding groove. This implies that TMEM106B, Vac7 and Tag1 may all be Lipid Transfer Proteins in the lumen of late endocytic organelles.
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Lipid Transfer Proteins: the Lipid commute via shuttles, bridges and tubes
Nature Reviews Molecular Cell Biology, 2019Co-Authors: Louise H. Wong, Alberto T. Gatta, Tim P. LevineAbstract:The distribution of Lipids largely depends on their non-vesicular transport by Lipid Transfer Proteins (LTPs). Recent progress in understanding the mechanisms of LTPs, including the appreciation of their widespread activity at membrane contact sites, has provided novel insights into the regulation of Lipid trafficking and how it impacts pathophysiology. Lipids are distributed in a highly heterogeneous fashion in different cellular membranes. Only a minority of Lipids achieve their final intracellular distribution through transport by vesicles. Instead, the bulk of Lipid traffic is mediated by a large group of Lipid Transfer Proteins (LTPs), which move small numbers of Lipids at a time using hydrophobic cavities that stabilize Lipid molecules outside membranes. Although the first LTPs were discovered almost 50 years ago, most progress in understanding these Proteins has been made in the past few years, leading to considerable temporal and spatial refinement of our understanding of the function of these Lipid transporters. The number of known LTPs has increased, with exciting discoveries of their multimeric assembly. Structural studies of LTPs have progressed from static crystal structures to dynamic structural approaches that show how conformational changes contribute to Lipid handling at a sub-millisecond timescale. A major development has been the finding that many intracellular LTPs localize to two organelles at the same time, forming a shuttle, bridge or tube that links donor and acceptor compartments. The understanding of how different Lipids achieve their final destination at the molecular level allows a better explanation of the range of defects that occur in diseases associated with Lipid transport and distribution, opening up the possibility of developing therapies that specifically target Lipid Transfer.
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Lipid Transfer Proteins the Lipid commute via shuttles bridges and tubes
Nature Reviews Molecular Cell Biology, 2019Co-Authors: Louise H. Wong, Alberto T. Gatta, Tim P. LevineAbstract:Lipids are distributed in a highly heterogeneous fashion in different cellular membranes. Only a minority of Lipids achieve their final intracellular distribution through transport by vesicles. Instead, the bulk of Lipid traffic is mediated by a large group of Lipid Transfer Proteins (LTPs), which move small numbers of Lipids at a time using hydrophobic cavities that stabilize Lipid molecules outside membranes. Although the first LTPs were discovered almost 50 years ago, most progress in understanding these Proteins has been made in the past few years, leading to considerable temporal and spatial refinement of our understanding of the function of these Lipid transporters. The number of known LTPs has increased, with exciting discoveries of their multimeric assembly. Structural studies of LTPs have progressed from static crystal structures to dynamic structural approaches that show how conformational changes contribute to Lipid handling at a sub-millisecond timescale. A major development has been the finding that many intracellular LTPs localize to two organelles at the same time, forming a shuttle, bridge or tube that links donor and acceptor compartments. The understanding of how different Lipids achieve their final destination at the molecular level allows a better explanation of the range of defects that occur in diseases associated with Lipid transport and distribution, opening up the possibility of developing therapies that specifically target Lipid Transfer.
Jean-claude Kader - One of the best experts on this subject based on the ideXlab platform.
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Lipid Transfer Proteins
Advanced Research on Plant Lipids, 2003Co-Authors: Jean-claude Kader, Françoise Guerbette, Ch. Vergnolle, Alain ZachowskiAbstract:Proteins capable of Transferring Lipids between membranes in vitro have been purified from a wide range of living organisms.The best known Proteins of this category in higher plants are Lipid Transfer Proteins (LTPs) which are able to Transfer several different phosphoLipids between membranes and to bind fatty acids and acyl-CoA esters (Yamada, 1992; Kader, 1996, 1997). LTPs were initially supposed to participate to membrane biogenesis and to intracellulair Lipid trafficking. However, no clear evidence of such roles have been demonstrated in vivo. Instead, LTPs are suggested to be involved in extracellular functions linked to defense reactions, in signaling mechanisms operating between pathogens and plants and in allergenic processes. In order to validate these hypotheses, it is of high interest to follow a genomic approach and to study the regulation of the expression of LTP genes by various abiotic and biotic stresses. These studies have been performed in Arabidopsis thaliana since its genome has been recently sequenced.
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Lipid Transfer Proteins are encoded by a small multigene family in arabidopsis thaliana
Plant Science, 2000Co-Authors: Vincent Arondel, Ch. Vergnolle, Catherine Cantrel, Jean-claude KaderAbstract:Lipid Transfer Proteins (LTPs) are small, basic and abundant Proteins in higher plants. They are capable of binding fatty acids and of Transferring phosphoLipids between membranes in vitro. LTPs from this family contain a signal peptide and are secreted in the cell wall. Their biological function is presently unknown. LTPs have been suggested to participate to cutin assembly and to the defense of the plants against pathogens. A genetic approach should prove useful to provide clues on their in vivo functions. Here, the characterization of the LTP gene family in Arabidopsis thaliana is described. At least 15 genes were identified, their map position determined and the expression pattern characterized for six of them. All the sequences exhibit the typical features of plant LTPs. The molecular weight is close to 9 kDa, the isoelectric point is near 9 (except for three acidic LTPs), and typical amino acid residues such as cysteines are conserved. Genomic DNA blotting hybridization experiments performed using ltp1 to ltp6 as probes indicate that ltps form distinct 1-3 gene subfamilies which do not cross hybridize. Expression studies indicate that all the genes tested are expressed in flowers and siliques, but not in roots. Ltp1, ltp5 and ltp2 are expressed significantly in leaves, while ltp6 is detected only in 2-4-week-old leaves. In addition, ltp4 and ltp3 are strongly upregulated by abscisic acid (ABA). Tandem repeats can be noted concerning ltp1 and ltp2 on chromosome 2, ltp3 and ltp4 on chromosome 5 and ltp5 and ltp12 on chromosome 3. While ltp7, ltp8 and ltp9 map at the same position on chromosome 2, the other genes are dispersed throughout the genome. The characterization of the Arabidopsis ltp gene family will permit to initiate a genetic approach for determining the in vivo function(s) of these Proteins.
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Lipid Transfer Proteins a puzzling family of plant Proteins
Trends in Plant Science, 1997Co-Authors: Jean-claude KaderAbstract:Lipid-Transfer Proteins are small, basic Proteins, and have been purified from various plant sources. They are able to Transfer Lipids between membranes in vitro and, on the basis of this, were initially thought to participate in the intracellular flux of Lipids during membrane synthesis. However, the finding that these Proteins are located in the cell wall and can be secreted has led to the suggestion that they are not required for intracellular Lipid transport. Instead, they may be involved in cutin biosynthesis, surface wax formation, pathogen-defence reactions, or the adaptation of plants to environmental changes.
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Lipid-Transfer Proteins IN PLANTS
Annual review of plant physiology and plant molecular biology, 1996Co-Authors: Jean-claude KaderAbstract:Lipid-Transfer Proteins (LTP) are basic, 9-kDa Proteins present in high amounts (as much as 4% of the total soluble Proteinss) in higher plants. LTPs can enhance the in vitro Transfer of phosphoLipids between membranes and can bind acyl chains. On the basis of these properties, LTPs were thought to participate in membrane biogenesis and regulation of the intracellular fatty acid pools. However, the isolation of several cDNAs and genes revealed the presence of a signal peptide indicating that LTPs could enter the secretory pathway. They were found to be secreted and located in the cell wall. Thus, novel roles were suggested for plant LTPs: participation in cutin formation, embryogenesis, defense reactions against phytopathogens, symbiosis, and the adaptation of plants to various environmental conditions. The validity of these suggestions needs to be determined, in the hope that they will elucidate the role of this puzzling family of plant Proteins.
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a potent antimicrobial protein from onion seeds showing sequence homology to plant Lipid Transfer Proteins
Plant Physiology, 1995Co-Authors: Bruno P. A. Cammue, Françoise Guerbette, Inge J W M Goderis, R W Osborn, Jan Van Damme, Kristel Eggermont, M. Hendriks, Karin Thevissen, Paul Proost, Jean-claude KaderAbstract:An antimicrobial protein of about 10 kD, called Ace-AMP1, was isolated from onion (Allium cepa L.) seeds. Based on the near-complete amino acid sequence of this protein, oligonucleotides were designed for polymerase chain reaction-based cloning of the corresponding cDNA. The mature protein is homologous to plant nonspecific Lipid Transfer Proteins (nsLTPs), but it shares only 76% of the residues that are conserved among all known plant nsLTPs and is unusually rich in arginine. Ace-AMP1 inhibits all 12 tested plant pathogenic fungi at concentrations below 10 [mu]g mL-1. Its antifungal activity is either not at all or is weakly affected by the presence of different cations at concentrations approximating physiological ionic strength conditions. Ace-AMP1 is also active on two Gram-positive bacteria but is apparently not toxic for Gram-negative bacteria and cultured human cells. In contrast to nsLTPs such as those isolated from radish or maize seeds, Ace-AMP1 was unable to Transfer phosphoLipids from liposomes to mitochondria. On the other hand, Lipid Transfer Proteins from wheat and maize seeds showed little or no antimicrobial activity, whereas the radish Lipid Transfer protein displayed antifungal activity only in media with low cation concentrations. The relevance of these findings with regard to the function of nsLTPs is discussed.