Component of the very low density lipoprotein (VLDL) fraction in plasma, and is an activator of several triacylglycerol lipases. The association of APOC2 with plasma chylomicrons, VLDL, and HDL is reversible, a function of the secretion and catabolism of triglyceride-rich lipoproteins, and changes rapidly.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
J. Lipid Res. 34, 1717-1727 (1993)[PubMed:8245722]
We wished to determine whether apolipoprotein C-IIToronto, a mutant form of apolipoprotein C-II that contains a C-terminal cysteine residue, exists as a monomeric species or as multiple disulfide-linked species in plasma lipoproteins. The plasma lipoproteins from a heterozygous carrier and two homozygous carriers of apoC-IIToronto were investigated. The mutant apolipoprotein was found in homodimeric form and as heterodimers with apolipoprotein A-II, apolipoprotein B-100, and apolipoprotein E. Of particular interest was the demonstration of the existence of the disulfide-linked species apolipoprotein B-100:A-II and B-100:C-IIToronto in the very low density and low density lipoproteins in subjects who were carriers of apoC-IIToronto. We also observed that apoE3:C-IIToronto and apoE3:A-II dimers were present in the chylomicrons and very low density lipoproteins of these subjects. The observation of the existence of apolipoprotein B-100:A-II was extended to other hypercholesterolemic and hypertriglyceridemic subjects. The highest proportion of apolipoprotein B-100:A-II was observed in the very low density lipoproteins of hypertriglyceridemic subjects. The concentration of this species was significantly higher in hyperlipidemic subjects than in normolipidemic controls. These results demonstrate that the molecular species of cysteine-containing apolipoproteins are complex and should be considered in studies of human lipoprotein composition and function.
ABCAI, a member of the ATP binding cassette family, mediates the efflux of excess cellular lipid to HDL and is defective in Tangier disease. The apolipoprotein acceptor specificity for lipid efflux by ABCAI was examined in stably transfected Hela cells, expressing a human ABCAI-GFP fusion protein. ApoA-I and all of the other exchangeable apolipoproteins tested (apoA-II, apoA-IV, apoC-I, apoC-II, apoC-III, apoE) showed greater than a threefold increase in cholesterol and phospholipid efflux from ABCAI-GFP transfected cells compared to control cells. Expression of ABCAI in Hela cells also resulted in a marked increase in specific binding of both apoA-I (Kd = 0.60 microg/mL) and apoA-II (Kd = 0.58 microg/mL) to a common binding site. In summary, ABCAI-mediated cellular binding of apolipoproteins and lipid efflux is not specific for only apoA-I but can also occur with other apolipoproteins that contain multiple amphipathic helical domains.
Plasma low- and high-density lipoproteins (LDL and HDL) are cleared from the circulation by specific receptors and are either totally degraded or their cholesteryl esters (CE) are selectively delivered to cells by receptors such as the scavenger receptor class B type I (SR-BI). The aim of the present study was to define the effect of apoC-II and apoC-III on the uptake of LDL and HDL by HepG2 cells. Stable transformants were obtained with sense or antisense strategies that secrete 47-294% the normal level of apoC-II or 60-200% that of apoC-III. Different levels of secreted apoC-II or apoC-III had little effect on LDL and HDL protein degradation by HepG2 cells. However, compared to controls, cells under-expressing apoC-II showed a 160% higher capacity to selectively take up HDL-CE, while cells under-expressing apoC-III demonstrated 70 and 160% higher capacity to take up CE from LDL and HDL, respectively. In experiments conducted with exogenously added apoC-II or apoC-III, no significant effect was observed on lipoprotein-protein association/degradation; however, LDL-CE and HDL-CE selective uptake was significantly reduced in a dose-dependent manner. These results indicate that apoC-II and apoC-III inhibit CE-selective uptake.
The process in which a chylomicron remnant is removed from the blood via receptor-mediated endocytosis into liver cells and its constituent parts degraded.
Like rat C apolipoproteins, each of the C apolipoproteins from human blood plasma (C-I, C-II, C-III-1, and C-III-2) bound to small chylomicrons from mesenteric lymph of estradiol-treated rats and inhibited their uptake by the isolated perfused rat liver. This inhibitory effect of the C apolipoproteins was independent of apolipoprotein E, which is present only in trace amounts in these chylomicrons. Addition of rat apolipoprotein E to small chylomicrons from mesenteric lymph of normal rats did not displace C apolipoproteins and had no effect on the uptake of these particles by the perfused liver, indicating that an increased ratio of E apolipoproteins to C apolipoproteins on chylomicron particles, unaccompanied by depletion of the latter, may not promote recognition by the chylomicron remnant receptor. The hepatic uptake of remnants of rat hepatic very low density lipoproteins (VLDL) and small chylomicrons, which had been produced in functionally eviscerated rats, was also inhibited by addition of C apolipoproteins. These observations are consistent with the hypothesis that the addition of all of the C apolipoproteins to newly secreted chylomicrons and VLDL inhibits premature uptake of these particles by the liver and that depletion of all of these apolipoproteins from remnant particles facilitates their hepatic uptake. Remnants of chylomicrons and VLDL incubated with rat C apolipoproteins efficiently took up C-III apolipoproteins, but not apolipoprotein C-II (the activator protein for lipoprotein lipase). Preferential loss of apolipoprotein C-II during remnant formation may regulate the termination of triglyceride hydrolysis prior to complete removal of triglycerides from chylomicrons and VLDL.
The acquisition, loss or modification of a protein or lipid within a chylomicron, including the hydrolysis of triglyceride by lipoprotein lipase and the subsequent loss of free fatty acid.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
The process in which a high-density lipoprotein particle is removed from the blood via receptor-mediated endocytosis and its constituent parts degraded.
Plasma low- and high-density lipoproteins (LDL and HDL) are cleared from the circulation by specific receptors and are either totally degraded or their cholesteryl esters (CE) are selectively delivered to cells by receptors such as the scavenger receptor class B type I (SR-BI). The aim of the present study was to define the effect of apoC-II and apoC-III on the uptake of LDL and HDL by HepG2 cells. Stable transformants were obtained with sense or antisense strategies that secrete 47-294% the normal level of apoC-II or 60-200% that of apoC-III. Different levels of secreted apoC-II or apoC-III had little effect on LDL and HDL protein degradation by HepG2 cells. However, compared to controls, cells under-expressing apoC-II showed a 160% higher capacity to selectively take up HDL-CE, while cells under-expressing apoC-III demonstrated 70 and 160% higher capacity to take up CE from LDL and HDL, respectively. In experiments conducted with exogenously added apoC-II or apoC-III, no significant effect was observed on lipoprotein-protein association/degradation; however, LDL-CE and HDL-CE selective uptake was significantly reduced in a dose-dependent manner. These results indicate that apoC-II and apoC-III inhibit CE-selective uptake.
The chemical reactions and pathways resulting in the breakdown of lipids, compounds soluble in an organic solvent but not, or sparingly, in an aqueous solvent.
Any process that stops, prevents, or reduces the frequency, rate or extent of the directed movement of cholesterol into, out of or within a cell, or between cells, by means of some agent such as a transporter or pore.
Plasma low- and high-density lipoproteins (LDL and HDL) are cleared from the circulation by specific receptors and are either totally degraded or their cholesteryl esters (CE) are selectively delivered to cells by receptors such as the scavenger receptor class B type I (SR-BI). The aim of the present study was to define the effect of apoC-II and apoC-III on the uptake of LDL and HDL by HepG2 cells. Stable transformants were obtained with sense or antisense strategies that secrete 47-294% the normal level of apoC-II or 60-200% that of apoC-III. Different levels of secreted apoC-II or apoC-III had little effect on LDL and HDL protein degradation by HepG2 cells. However, compared to controls, cells under-expressing apoC-II showed a 160% higher capacity to selectively take up HDL-CE, while cells under-expressing apoC-III demonstrated 70 and 160% higher capacity to take up CE from LDL and HDL, respectively. In experiments conducted with exogenously added apoC-II or apoC-III, no significant effect was observed on lipoprotein-protein association/degradation; however, LDL-CE and HDL-CE selective uptake was significantly reduced in a dose-dependent manner. These results indicate that apoC-II and apoC-III inhibit CE-selective uptake.
Any process that stops, prevents, or reduces the frequency, rate or extent of receptor mediated endocytosis, the uptake of external materials by cells, utilizing receptors to ensure specificity of transport.
J. Biol. Chem. 266, 18259-18267 (1991)[PubMed:1917954]
The mechanism of inhibition by apolipoprotein C of the uptake and degradation of triglyceride-rich lipoproteins from human plasma via the low density lipoprotein (LDL) receptor pathway was investigated in cultured human skin fibroblasts. Very low density lipoprotein (VLDL) density subfractions and intermediate density lipoprotein (IDL) with or without added exogenous recombinant apolipoprotein E-3 were used. Total and individual (C-I, C-II, C-III-1, and C-III-2) apoC molecules effectively inhibited apoE-3-mediated cell metabolism of the lipoproteins through the LDL receptor, with apoC-I being most effective. When the incubation was carried out with different amounts of exogenous apoE-3 and exogenous apoC, it was shown that the ratio of apoE-3 to apoC determined the uptake and degradation of VLDL. Excess apoE-3 overcame, at least in part, the inhibition by apoC. ApoC, in contrast, did not affect LDL metabolism. Neither apoA-I nor apoA-II, two apoproteins that do not readily associate with VLDL, had any effect on VLDL cell metabolism. The inhibition of VLDL and IDL metabolism cannot be fully explained by interference of association of exogenous apoE-3 with or displacement of endogenous apoE from the lipoproteins. IDL is a lipoprotein that contains both apoB-100 and apoE. By using monoclonal antibodies 4G3 and 1D7, which specifically block cell interaction by apoB-100 and apoE, respectively, it was possible to assess the effects of apoC on either apoprotein. ApoC dramatically depressed the interaction of IDL with the fibroblast receptor through apoE, but had only a moderate effect on apoB-100. The study thus demonstrates that apoC inhibits predominantly the apoE-3-dependent interaction of triglyceride-rich lipoproteins with the LDL receptor in cultured fibroblasts and that the mechanism of inhibition reflects association of apoC with the lipoproteins and specific concentration-dependent effects on apoE-3 at the lipoprotein surface.
Negative regulation of very-low-density lipoprotein particle clearancedefinition[GO:0010916]
Any process that decreases the rate, frequency or extent of very-low-density lipoprotein particle clearance. Very-low-density lipoprotein particle clearance is the process in which a very-low-density lipoprotein particle is removed from the blood via receptor-mediated endocytosis and its constituent parts degraded.
J. Biol. Chem. 266, 18259-18267 (1991)[PubMed:1917954]
The mechanism of inhibition by apolipoprotein C of the uptake and degradation of triglyceride-rich lipoproteins from human plasma via the low density lipoprotein (LDL) receptor pathway was investigated in cultured human skin fibroblasts. Very low density lipoprotein (VLDL) density subfractions and intermediate density lipoprotein (IDL) with or without added exogenous recombinant apolipoprotein E-3 were used. Total and individual (C-I, C-II, C-III-1, and C-III-2) apoC molecules effectively inhibited apoE-3-mediated cell metabolism of the lipoproteins through the LDL receptor, with apoC-I being most effective. When the incubation was carried out with different amounts of exogenous apoE-3 and exogenous apoC, it was shown that the ratio of apoE-3 to apoC determined the uptake and degradation of VLDL. Excess apoE-3 overcame, at least in part, the inhibition by apoC. ApoC, in contrast, did not affect LDL metabolism. Neither apoA-I nor apoA-II, two apoproteins that do not readily associate with VLDL, had any effect on VLDL cell metabolism. The inhibition of VLDL and IDL metabolism cannot be fully explained by interference of association of exogenous apoE-3 with or displacement of endogenous apoE from the lipoproteins. IDL is a lipoprotein that contains both apoB-100 and apoE. By using monoclonal antibodies 4G3 and 1D7, which specifically block cell interaction by apoB-100 and apoE, respectively, it was possible to assess the effects of apoC on either apoprotein. ApoC dramatically depressed the interaction of IDL with the fibroblast receptor through apoE, but had only a moderate effect on apoB-100. The study thus demonstrates that apoC inhibits predominantly the apoE-3-dependent interaction of triglyceride-rich lipoproteins with the LDL receptor in cultured fibroblasts and that the mechanism of inhibition reflects association of apoC with the lipoproteins and specific concentration-dependent effects on apoE-3 at the lipoprotein surface.
ABCAI, a member of the ATP binding cassette family, mediates the efflux of excess cellular lipid to HDL and is defective in Tangier disease. The apolipoprotein acceptor specificity for lipid efflux by ABCAI was examined in stably transfected Hela cells, expressing a human ABCAI-GFP fusion protein. ApoA-I and all of the other exchangeable apolipoproteins tested (apoA-II, apoA-IV, apoC-I, apoC-II, apoC-III, apoE) showed greater than a threefold increase in cholesterol and phospholipid efflux from ABCAI-GFP transfected cells compared to control cells. Expression of ABCAI in Hela cells also resulted in a marked increase in specific binding of both apoA-I (Kd = 0.60 microg/mL) and apoA-II (Kd = 0.58 microg/mL) to a common binding site. In summary, ABCAI-mediated cellular binding of apolipoproteins and lipid efflux is not specific for only apoA-I but can also occur with other apolipoproteins that contain multiple amphipathic helical domains.
Any process that activates or increases the frequency, rate or extent of the chemical reactions and pathways resulting in the formation of fatty acids.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Transgenic and gene disruption experiments in mice have revealed that apolipoprotein (apo) A-V is a potent regulator of plasma triglyceride (TG) levels. To investigate the molecular basis of apoA-V function, the ability of isolated recombinant apoA-V to modulate lipoprotein lipase (LPL) activity was examined in vitro. With three distinct lipid substrate particles, including very low-density lipoprotein (VLDL), a TG/phospholipid emulsion, or dimyristoylphosphatidylcholine liposomes, apoA-V had little effect on LPL activity. In the absence or presence apolipoprotein C-II, apoA-V marginally inhibited LPL activity. On the other hand, apoA-V-dimyristoylphosphatidylcholine disc particles bound to heparin-Sepharose and were specifically eluted upon application of a linear gradient of NaCl. The interaction of apoA-V with sulfated glycosaminoglycans was further studied by surface plasmon resonance spectroscopy. ApoA-V showed strong binding to heparin-coated chips, and binding was competed by free heparin. ApoA-V enrichment enhanced binding of apoC-II-deficient chylomicrons and VLDL to heparin-coated chips. When LPL was first bound to the heparin-coated chip, apoA-V-enriched chylomicrons showed binding. Finally, human pre- and post-heparin plasma samples were subjected to immunoblot analysis with anti-apoA-V IgG. No differences in the amount of apoA-V present were detected. Taken together, the results show that apoA-V lipid complexes bind heparin and, when present on TG-rich lipoprotein particles, may promote their association with cell surface heparan sulfate proteoglycans. Through such interactions, apoA-V may indirectly affect LPL activity, possibly explaining its inverse correlation with plasma TG levels.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Any process that increases the rate, frequency, or extent of phospholipid catabolism, the chemical reactions and pathways resulting in the breakdown of phospholipids, any lipid containing phosphoric acid as a mono- or diester.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Positive regulation of very-low-density lipoprotein particle remodelingdefinition[GO:0010902]
Any process that increases the rate, frequency or extent of very-low-density lipoprotein particle remodeling. Very-low-density lipoprotein particle remodeling is the acquisition, loss or modification of a protein or lipid within a very-low-density lipoprotein particle, including the hydrolysis of triglyceride by hepatic lipase or lipoprotein lipase and the subsequent loss of free fatty acid.
Apolipoprotein C-II (apoC-II) is an exchangeable plasma apolipoprotein and an endogenous activator of lipoprotein lipase (LpL). Genetic deficiencies of apoC-II and overexpression of apoC-II in transgenic mice are both associated with severe hyperlipidemia, indicating a complex role for apoC-II in the regulation of blood lipid levels. ApoC-II exerts no effect on the activity of LpL for soluble substrates, suggesting that activation occurs via the formation of a lipid-bound complex. We have synthesized a peptide corresponding to amino acid residues 39-62 of mature human apoC-II. This peptide does not bind to model lipid surfaces but retains the ability to activate LpL. Conjugation of the fluorophore 7-nitrobenz-2-oxa-1,3-diazole (NBD) to the N-terminal alpha-amino group of apoC-II39-62 facilitated determination of the affinity of the peptide for LpL using fluorescence anisotropy measurements. The dissociation constant describing this interaction was 0.23 microM, and was unchanged when LpL was lipid-bound. Competitive binding studies showed that apoC-II39-62 and full-length apoC-II exhibited the same affinity for LpL in aqueous solution, whereas the affinity for full-length apoC-II was increased at least 1 order of magnitude in the presence of lipid. We suggest that while the binding of apoC-II to the lipid surface promotes the formation of a high-affinity complex of apoC-II and LpL, activation occurs via direct helix-helix interactions between apoC-II39-62 and the loop covering the active site of LpL.
Plasma low- and high-density lipoproteins (LDL and HDL) are cleared from the circulation by specific receptors and are either totally degraded or their cholesteryl esters (CE) are selectively delivered to cells by receptors such as the scavenger receptor class B type I (SR-BI). The aim of the present study was to define the effect of apoC-II and apoC-III on the uptake of LDL and HDL by HepG2 cells. Stable transformants were obtained with sense or antisense strategies that secrete 47-294% the normal level of apoC-II or 60-200% that of apoC-III. Different levels of secreted apoC-II or apoC-III had little effect on LDL and HDL protein degradation by HepG2 cells. However, compared to controls, cells under-expressing apoC-II showed a 160% higher capacity to selectively take up HDL-CE, while cells under-expressing apoC-III demonstrated 70 and 160% higher capacity to take up CE from LDL and HDL, respectively. In experiments conducted with exogenously added apoC-II or apoC-III, no significant effect was observed on lipoprotein-protein association/degradation; however, LDL-CE and HDL-CE selective uptake was significantly reduced in a dose-dependent manner. These results indicate that apoC-II and apoC-III inhibit CE-selective uptake.
LPL and its specific physiological activator, apolipoprotein C-II (apoC-II), regulate the hydrolysis of triglycerides (TGs) from circulating TG-rich lipoproteins. Previously, we developed a skeletal muscle-specific LPL transgenic mouse that had lower plasma TG levels. ApoC-II transgenic mice develop hypertriglyceridemia attributed to delayed clearance. To investigate whether overexpression of LPL could correct this apoC-II-induced hypertriglyceridemia, mice with overexpression of human apoC-II (CII) were cross-bred with mice with two levels of muscle-specific human LPL overexpression (LPL-L or LPL-H). Plasma TG levels were 319 +/- 39 mg/dl in CII mice and 39 +/- 5 mg/dl in wild-type mice. Compared with CII mice, apoC-II transgenic mice with the higher level of LPL overexpression (CIILPL-H) had a 50% reduction in plasma TG levels (P = 0.013). Heart LPL activity was reduced by approximately 30% in mice with the human apoC-II transgene, which accompanied a more modest 10% decrease in total LPL protein. Overexpression of human LPL in skeletal muscle resulted in dose-dependent reduction of plasma TGs in apoC-II transgenic mice. Along with plasma apoC-II concentrations, heart and skeletal muscle LPL activities were predictors of plasma TGs. These data suggest that mice with the human apoC-II transgene may have alterations in the expression/activity of endogenous LPL in the heart. Furthermore, the decrease of LPL activity in the heart, along with the inhibitory effects of excess apoC-II, may contribute to the hypertriglyceridemia observed in apoC-II transgenic mice.
The acquisition, loss or modification of a protein or lipid within a triglyceride-rich lipoprotein particle, including the hydrolysis of triglyceride by lipoprotein lipase, with the subsequent loss of free fatty acid, and the transfer of cholesterol esters to a triglyceride-rich lipoprotein particle by cholesteryl ester transfer protein (CETP), with the simultaneous transfer of triglyceride from a triglyceride-rich lipoprotein particle.
LPL and its specific physiological activator, apolipoprotein C-II (apoC-II), regulate the hydrolysis of triglycerides (TGs) from circulating TG-rich lipoproteins. Previously, we developed a skeletal muscle-specific LPL transgenic mouse that had lower plasma TG levels. ApoC-II transgenic mice develop hypertriglyceridemia attributed to delayed clearance. To investigate whether overexpression of LPL could correct this apoC-II-induced hypertriglyceridemia, mice with overexpression of human apoC-II (CII) were cross-bred with mice with two levels of muscle-specific human LPL overexpression (LPL-L or LPL-H). Plasma TG levels were 319 +/- 39 mg/dl in CII mice and 39 +/- 5 mg/dl in wild-type mice. Compared with CII mice, apoC-II transgenic mice with the higher level of LPL overexpression (CIILPL-H) had a 50% reduction in plasma TG levels (P = 0.013). Heart LPL activity was reduced by approximately 30% in mice with the human apoC-II transgene, which accompanied a more modest 10% decrease in total LPL protein. Overexpression of human LPL in skeletal muscle resulted in dose-dependent reduction of plasma TGs in apoC-II transgenic mice. Along with plasma apoC-II concentrations, heart and skeletal muscle LPL activities were predictors of plasma TGs. These data suggest that mice with the human apoC-II transgene may have alterations in the expression/activity of endogenous LPL in the heart. Furthermore, the decrease of LPL activity in the heart, along with the inhibitory effects of excess apoC-II, may contribute to the hypertriglyceridemia observed in apoC-II transgenic mice.
The acquisition, loss or modification of a protein or lipid within a very-low-density lipoprotein particle, including the hydrolysis of triglyceride by hepatic lipase or lipoprotein lipase and the subsequent loss of free fatty acid.
Plasma low- and high-density lipoproteins (LDL and HDL) are cleared from the circulation by specific receptors and are either totally degraded or their cholesteryl esters (CE) are selectively delivered to cells by receptors such as the scavenger receptor class B type I (SR-BI). The aim of the present study was to define the effect of apoC-II and apoC-III on the uptake of LDL and HDL by HepG2 cells. Stable transformants were obtained with sense or antisense strategies that secrete 47-294% the normal level of apoC-II or 60-200% that of apoC-III. Different levels of secreted apoC-II or apoC-III had little effect on LDL and HDL protein degradation by HepG2 cells. However, compared to controls, cells under-expressing apoC-II showed a 160% higher capacity to selectively take up HDL-CE, while cells under-expressing apoC-III demonstrated 70 and 160% higher capacity to take up CE from LDL and HDL, respectively. In experiments conducted with exogenously added apoC-II or apoC-III, no significant effect was observed on lipoprotein-protein association/degradation; however, LDL-CE and HDL-CE selective uptake was significantly reduced in a dose-dependent manner. These results indicate that apoC-II and apoC-III inhibit CE-selective uptake.
Protein involved in the breakdown of lipids, a diverse class of compounds, insoluble in water but soluble in organic solvents, and which include fats, oils, triacylglycerols, fatty acids, glycolipids, phospholipids and steroids.
Protein involved in the biochemical reactions of lipids. Lipids are a diverse class of compounds which are insoluble in water but soluble in organic solvents. They include fats, oils, triacylglycerols, fatty acids, glycolipids, phospholipids and steroids.
Protein involved in the transport of lipids, a diverse class of compounds which are insoluble in water but soluble in organic solvents. They include fats, oils, triacylglycerols, fatty acids, glycolipids, phospholipids and steroids.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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