Role Of Lipid Transfer Proteins Research Articles

PtLTPG14-PtGAPC1 mediates lipid metabolism and glycolmetabolism in popular by G3P regulatory loop

Lipid comprises the basic skeleton of the plasma membrane and provides energy in various biological life activities. Although the essential roles of lipid transfer proteins (LTPs) have been proven in transporting lipids, the detailed feedback regulatory between lipid and carbohydrate metabolisms has not previously been identified in poplar (Populus trichocarpa). Here, poplar glycosylphosphatidylinositol-anchored lipid transfer protein gene PtLTPG14, as a homologous gene with Arabidopsis LTPG1, has been associated with fatty acids (FAs). The overexpression of PtLTPG14 not only has effects on the lipid derivatives, including unsaturated FAs (UFAs), medium-chain FAs (MCFAs), and long-chain FAs (LCFAs) but also has significantly down-regulated carbohydrate metabolites. A series of putative proteins interacting with PtLTPG14, including poplar cytosolic glyceraldehyde-3-phosphate dehydrogenase1 (PtGAPC1), have been identified by pull-down assays and PtLTPG14 displayed strong interaction with PtGAPC1 in vivo. PtLTPG14-overexpressed (OE) poplars exhibited higher abundances of FA biosynthetic genes and higher transcript levels of PtGAPC1. Therefore, PtLTPG14 can regulate expression levels of FA biosynthetic genes and PtLTPG14-PtGAPC1 complex participants in lipid and glucose metabolisms through regulating glyceraldehyde-3-phosphate (G3P) accumulation in poplar. The information showed that the comprehensive feedback regulatory loop among PtLTPG14, PtGAPC1, and G3P is implicated in lipid and glucose metabolisms.

Role of Lipid Transfer Proteins (LTPs) in the Viral Life Cycle.

Viruses are obligate parasites that depend on the host cell machinery for their replication and dissemination. Cellular lipids play a central role in multiple stages of the viral life cycle such as entry, replication, morphogenesis, and egress. Most viruses reorganize the host cell membranes for the establishment of viral replication complex. These specialized structures allow the segregation of replicating viral RNA from ribosomes and protect it from host nucleases. They also facilitate localized enrichment of cellular components required for viral replication and assembly. The specific composition of the lipid membrane governs its ability to form negative or positive curvature and possess a rigid or flexible form, which is crucial for membrane rearrangement and establishment of viral replication complexes. In this review, we highlight how different viruses manipulate host lipid transfer proteins and harness their functions to enrich different membrane compartments with specific lipids in order to facilitate multiple aspects of the viral life cycle.

Guard cell redox proteomics reveals a role of lipid transfer protein in plant defense

Redox-based post-translational modifications (PTMs) involving protein cysteine residues as redox sensors are important to various physiological processes. However, little is known about redox-sensitive proteins in guard cells and their functions in stomatal immunity. In this study, we applied an integrative protein labeling method cysTMTRAQ, and identified guard cell proteins that were altered by thiol redox PTMs in response to a bacterial flagellin peptide flg22. In total, eight, seven and 20 potential redox-responsive proteins were identified in guard cells treated with flg22 for 15, 30 and 60 min, respectively. The proteins fall into several functional groups including photosynthesis, lipid binding, oxidation-reduction, and defense. Among the proteins, a lipid transfer protein (LTP)-II was confirmed to be redox-responsive and involved in plant resistance to Pseudomonas syringe pv. tomato DC3000. This study not only creates an inventory of potential redox-sensitive proteins in flg22 signal transduction in guard cells, but also highlights the biological relevance of the lipid transfer protein in plant defense against bacterial pathogens. SignificanceProtein redox modifications play important roles in many physiological processes. However, redox proteomics has rarely been studied in plant single cell-types. In this study, isobaric tandem mass tag-based redox proteomics technology was applied to discover redox-sensitive proteins and corresponding cysteine residues in guard cell response to a bacterial flagellin peptide flg22. Many redox-responsive proteins related to photosynthesis, lipid binding, oxidation-reduction, and defense were identified. Using reverse genetics and biochemical analyses, a lipid transfer protein was functionally characterized to be involved in plant defense against pathogens. The study highlights the utility of redox proteomics in discovering new proteins and redox modifications in important stomatal guard cell functions. Furthermore, detailed functional characterization demonstrates the biological relevance of the redox-responsive lipid transfer protein in plant pathogen defense.

Role of lipid transfer proteins in loading CD1 antigen-presenting molecules

Research to connect lipids with immunology is growing, but details about the specific roles of lipid transfer proteins (LTPs) in antigen presentation remain unclear. A single class of major histocompatibility class-like molecules, called CD1 molecules, can present lipids and glycolipids to the immune system. These molecules all have a common hydrophobic antigen-binding groove. The loading of this groove with various lipids throughout the life of a CD1 molecule defines the immune recognition of lipids by T cells. At each location of residence, CD1 molecules are exposed to particular physicochemical conditions, particular collections of lipids, and unique combinations of LTPs that will define which lipids bind to CD1 and which do not. The lipid transfer machinery that is used by CD1 molecules is entirely hijacked from the normal synthetic and catalytic pathways of lipids. The precise determinants that regulate the presentation of certain lipids over others with respect to chemistry, solubility, and abundance are still poorly defined and require investigation to allow the use of lipids as regular antigenic targets of immunotherapy and vaccine.

Role of Lipid Transfer Proteins at ER-Golgi Membrane Contact Sites during Bunyavirus Infection.

Role of Lipid Transfer Proteins at ER-Golgi Membrane Contact Sites during Bunyavirus Infection.

Lipid transfer proteins in the assembly of apoB-containing lipoproteins

A better understanding of intracellular lipoprotein assembly may help identify proteins with important roles in lipid disorders. apoB-containing lipoproteins (B-lps) are macromolecular lipid and protein micelles that act as specialized transport vehicles for hydrophobic lipids. They are assembled predominantly in enterocytes and hepatocytes to transport dietary and endogenous fat, respectively, to different tissues. Assembly occurs in the endoplasmic reticulum (ER) and is dependent on lipid resynthesis in the ER and on a chaperone, namely, microsomal triglyceride transfer protein (MTTP). Precursors for lipid synthesis are obtained from extracellular sources and from cytoplasmic lipid droplets. MTTP is the major and essential lipid transfer protein that transfers phospholipids and triacylglycerols to nascent apoB for the assembly of lipoproteins. Assembly is aided by cell death-inducing DFF45-like effector B and by phospholipid transfer protein, which may facilitate additional deposition of triacylglycerols and phospholipids, respectively, to apoB. Here, we summarize the current understanding of the different steps in the assembly of B-lps and discuss the role of lipid transfer proteins in these steps to help identify new clinical targets for lipid-associated disorders, such as heart disease.

Topological organisation of the phosphatidylinositol 4,5-bisphosphate-phospholipase C resynthesis cycle: PITPs bridge the ER-PM gap.

Phospholipase C (PLC) is a receptor-regulated enzyme that hydrolyses phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at the plasma membrane (PM) triggering three biochemical consequences, the generation of soluble inositol 1,4,5-trisphosphate (IP3), membrane-associated diacylglycerol (DG) and the consumption of PM PI(4,5)P2 Each of these three signals triggers multiple molecular processes impacting key cellular properties. The activation of PLC also triggers a sequence of biochemical reactions, collectively referred to as the PI(4,5)P2 cycle that culminates in the resynthesis of this lipid. The biochemical intermediates of this cycle and the enzymes that mediate these reactions are topologically distributed across two membrane compartments, the PM and the endoplasmic reticulum (ER). At the PM, the DG formed during PLC activation is rapidly converted into phosphatidic acid (PA) that needs to be transported to the ER where the machinery for its conversion into PI is localised. Conversely, PI from the ER needs to be rapidly transferred to the PM where it can be phosphorylated by lipid kinases to regenerate PI(4,5)P2 Thus, two lipid transport steps between membrane compartments through the cytosol are required for the replenishment of PI(4,5)P2 at the PM. Here, we review the topological constraints in the PI(4,5)P2 cycle and current understanding how these constraints are overcome during PLC signalling. In particular, we discuss the role of lipid transfer proteins in this process. Recent findings on the biochemical properties of a membrane-associated lipid transfer protein of the PITP family, PITPNM proteins (alternative name RdgBα/Nir proteins) that localise to membrane contact sites are discussed. Studies in both Drosophila and mammalian cells converge to provide a resolution to the conundrum of reciprocal transfer of PA and PI during PLC signalling.

The role of Lipid transfer proteins in membrane trafficking and signal transduction

Lipid transfer proteins (LTPs) were initially discovered as soluble factors that accelerate the transfer of different lipid species between membranes in vitro. Since then, many LTPs have been isolated, cloned, crystallized and extensively studied for over 30 years. The mechanisms by which LTPs transfer lipids between bilayers in vitro have been established by numerous studies. Yet, their actual functions in intact cells remain largely controversial. Extensive studies on LTPs from plants, yeast and mammals suggest that LTPs regulate multiple cellular processes including vesicular trafficking, signal transduction and lipid metabolism. Our studies on certain LTPs with different lipid‐transfer specificity demonstrated their influence on intracellular lipid distribution; shed light on their mechanisms of action in intact cells, and their coordinated lipid transfer activity. Furthermore, our studies on the Nir2 protein, a large protein consisting of an N‐terminal phsphatidylinositol (PI)‐transfer domain, demonstrate its regulatory role in membrane trafficking events and signal transduction cascades. We will discuss our recent findings and describe our general view on LTPs and their mode of action in intact cells.

The Role of Lipid Transfer Proteins in Allergic Diseases

Nonspecific lipid transfer proteins (LTPs) are important allergens in fruits, vegetables, nuts, pollen, and latex. Despite their wide distribution throughout the plant kingdom, their clinical relevance is largely confined to the Mediterranean area. As they can sensitize via the gastrointestinal tract, LPTs are considered true food allergens, and IgE reactivity to LTPs is often associated with severe systemic symptoms. Although Pru p 3 represents the predominant LTP in terms of patients' IgE recognition, the contribution of pollen LTPs in primary sensitization cannot be ruled out. Due to structural homology, LTPs from different allergen sources are generally IgE cross-reactive. However, sensitization profiles among allergic patients are extremely heterogeneous, and individual cross-reactivity patterns can be restricted to a single LTP or encompass many different LTPs. Molecule-based approaches in allergy research and diagnosis are important for better understanding of LTP allergy and could assist clinicians with providing adequate patient-tailored advice.

Differential Space-Time Expression of StLTPb1 Gene Between Resistant and Susceptible Potato Genotypes in Response to Ralstonia solanacearum

This study is to investigate the role of lipid transfer protein ( LTP1) gene of potato ( Solanum tuberosum) in bacterial wilt ( Ralstonia solanacearum) resistance. A novel cDNA clone encoding nsLTP was isolated from cultivated potato ( Solanum tuberosum) infected with R. solanacearum by 5′-rapid amplification of cDNA ends (RACE). The temporal and spatial expression of StLTPb1 was studied during the early stages of potato- R. solanacearum interaction by reverse transcriptase PCR (RT-PCR) and Northern blotting. The sequence analysis of the cloned cDNA, named StLTPb1, showed 691 bp which encoded a type 1 nsLTP of 91 amino acids. Construction of a phylogenic tree showed that StLTPb1 is well conserved in the coding region with high identity at the amino acid level with other Solanaceae nsLTPs. The temporal and spatial expression of StLTPb1 was studied during the early stages of potato- R. solanacearum interaction. StLTPb1 transcription is induced faster and transcripts accumulate to higher concentrations in resistant compared with susceptible genotypes by the pathogen. Dominant differences in the pathogen-induced gene expression pattern between the upper and lower leaves and stems were observed within the same genotypes. In situ hybridization results showed that the StLTPb1 mRNA was localized in phloem cells of vascular tissues in potato leaf and stem tissues after pathogen infection. Salicylic acid, methyl jasmonate and abscisic acid could induce StLTPb1 gene expression without significant difference between the upper and lower tissues. These abiotic elicitors could produce a long-lasting effect on the StLTPb1 during early stages of potato- R. solanacearum interaction. Differential expression of StLTPb1 gene between resistance and susceptible potato genotypes in response to R. solanacearum suggests that this gene plays a key role in plant defense mechanisms.

Lipid transfer protein activities in subjects with impaired glucose tolerance

Impaired glucose tolerance (IGT) is associated with an increased risk of atherosclerosis that may be due in part to dyslipidemia. The purpose of this study was to assess the regulatory role of lipid transfer proteins in the development of this dyslipidemia. Activities of cholesterol ester transfer protein (CETP) and phospholipid transfer protein (PLTP), as well as lipid and protein components of the major lipoprotein fractions, were evaluated in probands with IGT and were compared with those in subjects with normal glucose tolerance. The effect of a fat-rich meal on these variables was also investigated. IGT probands had a higher triglyceride content in subfractions of low- (LDL) and high-density lipoprotein (HDL). IGT patients had higher fasting CETP activity. The latter was positively correlated with HDL2 triglycerides and negatively with HDL3 total cholesterol. PLTP activity and mass were not higher in IGT patients. However, PLTP activity correlated with components of VLDL and LDL and was influenced by the type of obesity. Neither CETP and PLTP activities nor PLTP mass were altered by a fat-rich meal. PLTP and CETP activities correlated in both fasting and postprandial conditions. Increased fasting CETP activity may contribute to increased risk of atherosclerosis in subjects with IGT.

Specific Adduction of Plant Lipid Transfer Protein by an Allene Oxide Generated by 9-Lipoxygenase and Allene Oxide Synthase

Lipid transfer proteins (LTPs) are ubiquitous plant lipid-binding proteins that have been associated with multiple developmental and stress responses. Although LTPs typically bind fatty acids and fatty acid derivatives in a non-covalent way, studies on the LTPs of barley seeds have identified an abundantly occurring covalently modified form, LTP1b, the lipid ligand of which has resisted clarification. In the present study, this adduct was identified as the alpha-ketol 9-hydroxy-10-oxo-12(Z)-octadecenoic acid. Further studies on the formation of LTP1b demonstrated that the ligand was introduced by nucleophilic attack of the free carboxylate group of the Asp-7 residue of the protein at carbon-9 of the allene oxide fatty acid 9(S),10-epoxy-10,12(Z)-octadecadienoic acid. This reactive oxylipin was produced in barley seeds by oxygenation of linoleic acid by 9-lipoxygenase followed by dehydration of the resulting hydroperoxide by allene oxide synthase. The generation of protein-oxylipin adducts represents a new function for plant allene oxide synthases, enzymes that have earlier been implicated mainly in the biosynthesis of the jasmonate family of plant hormones. Additionally, the LTP-allene oxide synthase interaction opens new perspectives regarding the roles of LTPs in the signaling of plant defense and development.

Assessment of Lipid Transfer Protein ( LTP1) Gene in Wheat Powdery Mildew Resistance

This study is to investigate the role of lipid transfer protein ( LTP1) gene of wheat ( Triticum aestivum L.) in powdery mildew ( Blumeria graminis f.sp. tritici, Bgt) resistance. A pair of primers based on the full length cDNA of wheat LTP1 was used for amplifying the coding regions of LTP in hexaploid (AABBDD) wheat and its diploid donors T. urartu (AA), Ae. speltoides ssp speltoide (SS) and Ae. tauchii ssp strangulate (DD). LTP1 and LTP2 of wheat were isolated from the tested two hexaploid (ABD) materials: powdery mildew resistance near isogenic line (NIL) Mardler/7 × Bainong 3217 and its susceptible parent Bainong 3217 at the same time, while only one kind of LTP gene was found in the tested three diploid materials respectively by using the above PCR primer pairs. Two peaks of the expression of LTP1 and LTP2 induced by powdery mildew were observed [one occurred at 3 h after inoculation (hai); the other occurred at 10 hai] in resistant NIL Mardler/7 × Bainong3217 in comparison with a steady transcript level of LTP1 and LTP2 in susceptible Bainong3217. Transient over-expression result showed that LTP1 reduced the penetration efficiency (PE) of powdery mildew in susceptible cultivar by about 28.3%. This result indicated an obvious effectiveness of LTP1 in powdery mildew resistance. Expression analysis also showed that LTP1 and LTP2 of wheat are generally involved in salt/drought, but not in low temperature stress early responses.

Clinical role of lipid transfer proteins in food allergy

Lipid transfer proteins are widespread plant food allergens, highly resistant to food processing and to the gastrointestinal environment, which have recently been described as true food allergens in the Mediterranean area, where they have been associated with severe allergic reactions to foods in patients without pollen allergy. In this review we analyze their molecular structure, biological function, and clinical relevance in food allergy.

The Canadian Phytopathological Society Annual Meeting, Montréal, Quebec, 2003

The Canadian Phytopathological Society Annual Meeting, Montréal, Quebec, 2003

Phospholipid and cholesteryl ester transfer are increased in lipoprotein lipase deficiency.

Phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) are key enzymes in lipoprotein metabolism by mediating the transfer and exchange of phospholipids (PL) and neutral lipids between lipoproteins. Lipoprotein lipase (LPL) deficiency is associated with low HDL-cholesterol (HDL-C) levels in both, the homozygous and heterozygous state. In the present study we set out to investigate the role of lipid transfer proteins, which are known to strongly determine HDL-C levels, in LPL deficiency. Phospholipid acceptor and donor properties of lipoproteins, PLTP activity, CETP mass, activity and cholesteryl ester (CE) transfer were determined in two homozygous and six heterozygous LPL-deficient subjects and in 10 healthy, normolipidaemic controls, respectively. The HDL isolated from LPL-deficient subjects showed strongly increased PL-acceptance when compared with controls (homozygotes versus heterozygotes versus control: 26.46 +/- 15.26 vs. 3.41 +/- 1.61 vs. 1.89 +/- 0.33 micromol mL-1 h-1/micromol mL-1 PL; all P < 0.05). Phospholipid transfer from apolipoprotein B containing lipoproteins was increased in heterozygotes when compared with controls (46.66 +/- 23.3 vs. 28.91 +/- 18.05 micromol mL-1 h-1/micromol mL-1 PL, P = 0.05). PLTP activity, however, was similar in LPL-deficient subjects and controls. CETP mass was highest in homozygotes, whilst enzyme activity was similar in LPL-deficient subjects and controls. CE transfer was highest in homozygotes (72.5 +/- 8.8%) and lowest in controls (28.7 +/- 5.2%, P < 0.01). In conclusion, PL and CE transfer are increased in LPL deficiency and thus, partly explain low HDL-levels in LPL-deficient subjects. Enhanced transfer seems rather to be the result of altered lipoprotein composition and concentration than altered enzyme activity. Our findings on mechanisms leading to low HDL-C levels might show another aspect in atherogenesis in LPL deficiency.

Characterization of asparagus allergens: A relevant role of lipid transfer proteins

Background: No asparagus allergen has been characterized to date. Lipid transfer proteins (LTPs) have an ubiquitous distribution in plant foods and have been identified as relevant allergens in some fruits, seeds, and pollens. Objective: We sought to identify asparagus allergens and to evaluate the potential involvement of the panallergen LTP family in asparagus allergy. Methods: Eighteen patients with asthma, anaphylaxis, and/or contact urticaria after asparagus ingestion or exposure and positive skin prick test (SPT) responses and serum-specific IgE levels to asparagus were selected. Two LTPs were isolated from crude asparagus extract by using chromatographic methods and characterized by means of N-terminal amino acid sequencing. Both isolated proteins were tested by means of immunodetection, CAP inhibition assays, and SPTs. Additional asparagus allergens were located by using immunodetection with a pool of sera from patients allergic to asparagus and with rabbit polyclonal antibodies to sunflower pollen profilin and anti–complex asparagine-linked glycans antibodies. Results: The purified LTPs showed an N-terminal amino acid sequence similar to that of Pru p 3 and a strong reaction to anti-Pru p 3 antibodies. Each isolated protein reached inhibition values of up to 60% in CAP inhibition assays against asparagus extracts and elicited positive SPT responses in 9 of 18 patients with asparagus allergy. Immunodetection assays allowed us to identify profilin and cross-reacting carbohydrate determinants as asparagus IgE-binding components. Conclusion: Asparagus LTPs are relevant allergens. In addition, profilin and glycoproteins harboring complex asparagine-linked glycans can also be involved in asparagus allergy. (J Allergy Clin Immunol 2002;110:790-6.)

Effect of lipid transfer proteins on lipoprotein lipase induced transformation of VLDL and HDL

Lipoprotein lipase-induced lipolysis of human plasma VLDL usually does not yield a complete conversion of VLDL to LDL due to insufficient loss of surface and core lipids and apolipoprotein E. In order to assess the role of lipid transfer proteins in this process human VLDL and apo E free HDL, in approximately physiologic proportions, and with sufficient albumin to bind all released fatty acids, were subjected to 90% lipolysis of triglycerides in 2 h by lipoprotein lipase in the presence or absence of partially purified human cholesteryl ester and phospholipid transfer proteins. Lipoprotein lipase caused a partial transfer of VLDL unesterified cholesterol (16%) and phospholipid (11%), apo E (19%) and almost complete transfer of apo CII and CIII to HDL. VLDL remnants possessed excess apo E and surface and core lipids when compared to plasma LDL, and densities ranging from that of VLDL/IDL to LDL. With addition of the lipid transfer proteins to the lipolysis incubation there was an increased transfer of phospholipid and unesterified cholesterol (2-fold) and apo E (1.6-fold) to HDL over that for lipoprotein lipase incubations. The source of transferred material was primarily from remnants which isolated in the LDL density range in lipoprotein lipase incubations. This transfer resulted in LDL-like particles which had a smaller particle size but lighter density compared to those in lipoprotein lipase incubation. Transfer of cholesteryl esters to VLDL from HDL in exchange for triglyceride was absent or substantially reduced in incubations containing lipoprotein lipase and lipid transfer proteins compared to incubations with only lipid transfer proteins. It is concluded that during rapid lipolysis lipid transfer proteins promote the loss of phospholipid, unesterified cholesterol and apo E from VLDL remnants but do not promote the transfer of cholesteryl ester from HDL to VLDL.

Stimulation of human sperm capacitation by purified lipid transfer protein.

Lipid Transfer Protein I is recognized as a key component involved in high density lipoprotein metabolism. We have been studying lipid transfer in relation to sperm capacitation, a complex series of cell surface events required for the acrosome reaction and fertilization. We have previously shown that Lipid Transfer Protein I is present and active in the female reproductive tract. In the present study, we show that purified Lipid Transfer Protein I directly stimulates human sperm capacitation, but not the acrosome reaction, in the absence of other biological effectors. These results provide strong evidence for a novel role for Lipid Transfer Protein I and reveal, for the first time, a potent activator of capacitation, prior to the acrosome reaction.

Triglyceride transfer is required for net cholesteryl ester transfer between lipoproteins in plasma by lipid transfer protein. Evidence for a hetero-exchange transfer mechanism demonstrated by using novel monoclonal antibodies.

In order to investigate the role of lipid transfer protein (LTP) in plasma lipoprotein metabolism, monoclonal antibodies (mAbs) have been raised against LTP isolated from rabbit plasma. mAbs 2-8G and 3-9F inhibited both [3H]cholesteryl ester (CE) and [3H]triglyceride (TG) transfer from low density lipoprotein (LDL) to high density lipoprotein (HDL) mediated by LTP. Although 3-9F cross-reacted with human LTP, 2-8G was species-specific for rabbit LTP. mAb 14-8H inhibited only [3H]TG but not [3H]CE transfer and was cross-reactive with human LTP. mAbs 2-8G and 3-9F interfered with association of LTP with lipid microemulsions, again 2-8G with species specificity, whereas 14-8H did not affect LTP-microemulsion binding. Thus, mAbs 3-9F and 14-8H were used for further study in human plasma. By total inhibition of CE and TG transfer by 3-9F, LTP was shown to be responsible for net mass transfer of neutral lipids between lipoprotein classes in plasma, namely of CE from HDL to very low density lipoprotein (VLDL) and TG from VLDL to LDL and HDL. Selective inhibition of TG transfer by mAb 14-8H was also able to inhibit such net neutral lipid transfer. Such effect of these antibodies was demonstrated more remarkably in the presence of cholesterol esterification. Thus, TG transfer activity of LTP was shown to be required for net CE transfer, suggesting that net neutral lipid transfer in plasma between lipoproteins occurred mainly by a hetero-exchange mechanism. Inhibition of net neutral lipid transfer in plasma did not affect cholesterol esterification occurring predominantly on HDL. Consequently, mAb inhibition of TG transfer in plasma leads to CE accumulation in HDL. It is possible that hyperalphalipoproteinemia may be induced by a mutation in LTP that causes a selective defect in TG transfer activity.