The Experts below are selected from a list of 162 Experts worldwide ranked by ideXlab platform
Geoffrey J. Howlett - One of the best experts on this subject based on the ideXlab platform.
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Charge and charge-pair mutations alter the rate of assembly and structural properties of Apolipoprotein C-II amyloid fibrils.
Biochemistry, 2015Co-Authors: Chai Lean Teoh, Geoffrey J. Howlett, Paul R. Gooley, Shuo Yang, Courtney O. Zlatic, Zachary Rosenes, Michael D. W. GriffinAbstract:The misfolding, aggregation, and accumulation of proteins as amyloid fibrils is a defining characteristic of several debilitating diseases. Human Apolipoprotein C-II (apoC-II) amyloid fibrils are representative of the fibrils formed by a number of plasma Apolipoproteins implicated in amyloid-related disease. Previous structural analyses identified a buried charge pair between residues K30 and D69 within apoC-II amyloid fibrils. We have investigated the effects of amino acid substitutions of these residues on apoC-II fibril formation. Two point mutations of apoC-II, D69K and K30D, as well as a reversed ion-pair mutant containing both mutations (KDDK) were generated. Fibril formation by the double mutant, apoC-II KDDK, and apoC-II D69K was enhanced compared to that of wild-type (WT) apoC-II, while apoC-II K30D lacked the ability to form fibrils under standard conditions. Structural analyses showed that WT apoC-II, apoC-II D69K, and apoC-II KDDK fibrils have similar secondary structures and morphologies. Siz...
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The Role of Lipid in Misfolding and Amyloid Fibril Formation by Apolipoprotein C-II
Advances in Experimental Medicine and Biology, 2015Co-Authors: Timothy M. Ryan, Geoffrey J. Howlett, Michael D. W. GriffinAbstract:Apolipoproteins are a key component of lipid transport in the circulatory system and share a number of structural features that facilitate this role. When bound to lipoprotein particles, these proteins are relatively stable. However, in the absence of lipids they display conformational instability and a propensity to aggregate into amyloid fibrils. Apolipoprotein C-II (apoC-II) is a member of the Apolipoprotein family that has been well characterised in terms of its misfolding and aggregation. In the absence of lipid, and at physiological ionic strength and pH, apoC-II readily forms amyloid fibrils with a twisted ribbon-like morphology that are amenable to a range of biophysical and structural analyses. Consistent with its lipid binding function, the misfolding and aggregation of apoC-II are substantially affected by the presence of lipid. Short-chain phospholipids at submicellar concentrations significantly accelerate amyloid formation by inducing a tetrameric form of apoC-II that can nucleate fibril aggregation. Conversely, phospholipid micelles and bilayers inhibit the formation of apoC-II ribbon-type fibrils, but induce slow formation of amyloid with a distinct straight fibril morphology. Our studies of the effects of lipid at each stage of amyloid formation, detailed in this chapter, have revealed complex behaviour dependent on the chemical nature of the lipid molecule, its association state, and the protein:lipid ratio.
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Avoiding the oligomeric state: αB-crystallin inhibits fragmentation and induces dissociation of Apolipoprotein C-II amyloid fibrils
The FASEB Journal, 2012Co-Authors: Katrina J. Binger, Geoffrey J. Howlett, John A. Carver, Heath Ecroyd, Shuo Yang, Michael D. W. GriffinAbstract:The in vivo aggregation of proteins into amyloid fibrils suggests that cellular mechanisms that normally prevent or reverse this aggregation have failed. The small heat-shock molecular chaperone protein αB-crystallin (αB-c) inhibits amyloid formation and colocalizes with amyloid plaques; however, the physiological reason for this localization remains unexplored. Here, using Apolipoprotein C-II (apoC-II) as a model fibril-forming system, we show that αB-c binds directly to mature amyloid fibrils (Kd 5.4 ± 0.5 μM). In doing so, αB-c stabilized the fibrils from dilution-induced fragmentation, halted elongation of partially formed fibrils, and promoted the dissociation of mature fibrils into soluble monomers. Moreover, in the absence of dilution, the association of αB-c with apoC-II fibrils induced a 14-fold increase in average aggregate size, resulting in large fibrillar tangles reminiscent of protein inclusions. We propose that the binding of αB-c to fibrils prevents fragmentation and mediates the lateral a...
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Shear Flow Induced Changes in Apolipoprotein C-II Conformation and Amyloid Fibril Formation
Biochemistry, 2011Co-Authors: Chai Lean Teoh, Innocent B. Bekard, Peter Asimakis, Michael D. W. Griffin, Timothy M. Ryan, Dave E. Dunstan, Geoffrey J. HowlettAbstract:The misfolding and self-assembly of proteins into amyloid fibrils that occur in several debilitating diseases are affected by a variety of environmental factors, including mechanical factors associated with shear flow. We examined the effects of shear flow on amyloid fibril formation by human Apolipoprotein C-II (apoC-II). Shear fields (150, 300, and 500 s–1) accelerated the rate of apoC-II fibril formation (1 mg/mL) approximately 5–10-fold. Fibrils produced at shear rates of 150 and 300 s–1 were similar to the twisted ribbon fibrils formed in the absence of shear, while at 500 s–1, tangled ropelike structures were observed. The mechanism of the shear-induced acceleration of amyloid fibril formation was investigated at low apoC-II concentrations (50 μg/mL) where fibril formation does not occur. Circular dichroism and tryptophan fluorescence indicated that shear induced an irreversible change in apoC-II secondary structure. Fluorescence resonance energy transfer experiments using the single tryptophan resi...
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Lipids enhance Apolipoprotein C-II-derived amyloidogenic peptide oligomerization but inhibit fibril formation
Journal of Physical Chemistry B, 2009Co-Authors: Andrew Hung, Geoffrey J. Howlett, Michael D. W. Griffin, Irene YarovskyAbstract:We investigated the effect of submicellar lipids on amyloid fibril formation. Thioflavin T fluorescence studies showed that submicellar levels of the short-chain phospholipids, dipentanoylphosphatidylcholine and dihexanoylphosphatidylcholine, strongly in inhibited amyloid fibril formation by an 11-residue peptide derived from human Apolipoprotein C-II (apoC-II60?70). In contrast, sedimentation equilibrium analysis of these peptide?lipid mixtures indicated the presence of soluble oligomeric complexes. To acquire insight into the atomic level influences of these lipids on the initial stages of aggregation of the peptide, we performed molecular dynamics (MD) simulations coupled with umbrella sampling to determine dimerization free energies of a number of ?-stranded and random coil dimer complexes, both in the presence and absence of lipids. The simulations indicate that, in contrast to their inhibitory effects on fibril formation, short-chain phospholipids promote the formation and stabilization of dimers by enhancing intersubunit hydrophobic interactions. On the basis of these experimental and computational results, we propose that peptide-bound lipids can inhibit amyloid fibril formation by trapping of dimers and other oligomeric species in diverse nonfibril forming conformations, reducing their likelihood of acquiring subunit conformations prone to fibril nucleation and growth. In light of the demonstrated cytotoxicity of amyloid peptide oligomers, our results suggest that, by enhancing the stability of oligomeric peptide species, the presence of solvated lipids may contribute to the cytotoxicity of fibrillogenic proteins and peptides.
Danny M. Hatters - One of the best experts on this subject based on the ideXlab platform.
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Phospholipid Complexation and Association with Apolipoprotein C-II: Insights from Mass Spectrometry
Biophysical Journal, 2003Co-Authors: Charlotte L. Hanson, Leopold L. Ilag, Jonathan Malo, Danny M. Hatters, Geoffrey J. Howlett, Carol V. RobinsonAbstract:The interactions between phospholipid molecules in suspensions have been studied by using mass spectrometry. Electrospray mass spectra of homogeneous preparations formed from three different phospholipid molecules demonstrate that under certain conditions interactions between 90 and 100 lipid molecules can be preserved. In the presence of Apolipoprotein C-II, a phospholipid binding protein, a series of lipid molecules and the protein were observed in complexes. The specificity of binding was demonstrated by proteolysis; the resulting mass spectra reveal lipid-bound peptides that encompass the proposed lipid-binding domain. The mass spectra of heterogeneous suspensions and their complexes with Apolipoprotein C-II demonstrate that the protein binds simultaneously to two different phospholipids. Moreover, when Apolipoprotein C-II is added to lipid suspensions formed with local concentrations of the same lipid molecule, the protein is capable of remodeling the distribution to form one that is closer to a statistical arrangement. These observations demonstrate a capacity for Apolipoprotein C-II to change the topology of the phospholipid surface. More generally, these results highlight the fact that mass spectrometry can be used to probe lipid interactions in both homogeneous and heterogeneous suspensions and demonstrate reorganization of the distribution of lipids upon surface binding of Apolipoprotein C-II.
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The Circularization of Amyloid Fibrils Formed by Apolipoprotein C-II
Biophysical Journal, 2003Co-Authors: Danny M. Hatters, Cait E. Macphee, Christopher A. Macraild, Rob D. Daniels, Walraj S. Gosal, Neil H. Thomson, Jonathan A. Jones, Jason J. Davis, Christopher M. Dobson, Geoffrey J. HowlettAbstract:Amyloid fibrils have historically been characterized by diagnostic dye-binding assays, their fibrillar morphology, and a “cross-β” x-ray diffraction pattern. Whereas the latter demonstrates that amyloid fibrils have a common β-sheet core structure, they display a substantial degree of morphological variation. One striking example is the remarkable ability of human Apolipoprotein C-II amyloid fibrils to circularize and form closed rings. Here we explore in detail the structure of apoC-II amyloid fibrils using electron microscopy, atomic force microscopy, and x-ray diffraction studies. Our results suggest a model for apoC-II fibrils as ribbons ∼2.1-nm thick and 13-nm wide with a helical repeat distance of 53 nm ± 12 nm. We propose that the ribbons are highly flexible with a persistence length of 36 nm. We use these observed biophysical properties to model the apoC-II amyloid fibrils either as wormlike chains or using a random-walk approach, and confirm that the probability of ring formation is critically dependent on the fibril flexibility. More generally, the ability of apoC-II fibrils to form rings also highlights the degree to which the common cross-β superstructure can, as a function of the protein constituent, give rise to great variation in the physical properties of amyloid fibrils.
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Suppression of Apolipoprotein C‐II amyloid formation by the extracellular chaperone, clusterin
FEBS Journal, 2002Co-Authors: Danny M. Hatters, Mark R. Wilson, Simon B. Easterbrook-smith, Geoffrey J. HowlettAbstract:The effect of the extracellular chaperone, clusterin, on amyloid fibril formation by lipid-free human Apolipoprotein C-II (apoC-II) was investigated. Sub-stoichiometric levels of clusterin, derived from either plasma or semen, potently inhibit amyloid formation by apoC-II. Inhibition is dependent on apoC-II concentration, with more effective inhibition by clusterin observed at lower concentrations of apoC-II. The average sedimentation coefficient of apoC-II fibrils formed from apoC-II (0.3 mg·mL−1) is reduced by coincubation with clusterin (10 µg·mL−1). In contrast, addition of clusterin (0.1 mg·mL−1) to preformed apoC-II amyloid fibrils (0.3 mg·mL−1) does not affect the size distribution after 2 days. This sedimentation velocity data suggests that clusterin inhibits fibril growth but does not promote fibril dissociation. Electron micrographs indicate similar morphologies for amyloid fibrils formed in the presence or absence of clusterin. The substoichiometric nature of the inhibition suggests that clusterin interacts with transient amyloid nuclei leading to dissociation of the monomeric subunits. We propose a general role for clusterin in suppressing the growth of extracellular amyloid.
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Macromolecular Crowding Accelerates Amyloid Formation by Human Apolipoprotein C-II
Journal of Biological Chemistry, 2001Co-Authors: Danny M. Hatters, Allen P. Minton, Geoffrey J. HowlettAbstract:Abstract Human Apolipoprotein C-II (apoC-II) slowly forms amyloid fibers in lipid-free solutions at physiological pH and salt concentrations (Hatters, D. M., MacPhee, C. E., Lawrence, L. J., Sawyer, W. H., and Howlett, G. J. (2000)Biochemistry 39, 8276–8283). Measurements of the time dependence of solution turbidity, thioflavin T reactivity, and the amount of sedimentable aggregate reveal that the rate and extent of amyloid formation are significantly increased by the addition of an inert polymer, dextran T10, at concentrations exceeding 20 g/liter. High dextran concentrations do not alter the secondary structure of the protein, fiber morphology, or the thioflavin T and Congo Red binding capacity of apoC-II amyloid. Analytical ultracentrifugation studies show that monomeric apoC-II does not associate significantly with dextran. The observed dependence of the overall rate of amyloid formation on dextran concentration may be accounted for quantitatively by a simple model for nonspecific volume exclusion. The model predicts that an increase in the fractional volume occupancy of macromolecules in a physiological fluid can nonspecifically accelerate the formation of amyloid fibers by any amyloidogenic protein.
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The molecular chaperone, alpha-crystallin, inhibits amyloid formation by Apolipoprotein C-II.
Journal of Biological Chemistry, 2001Co-Authors: Danny M. Hatters, Robyn A. Lindner, John A. Carver, Geoffrey J. HowlettAbstract:Abstract Under lipid-free conditions, human Apolipoprotein C-II (apoC-II) exists in an unfolded conformation that over several days forms amyloid ribbons. We examined the influence of the molecular chaperone, α-crystallin, on amyloid formation by apoC-II. Time-dependent changes in apoC-II turbidity (at 0.3 mg/ml) were suppressed potently by substoichiometric subunit concentrations of α-crystallin (1–10 μg/ml). α-Crystallin also inhibits time-dependent changes in the CD spectra, thioflavin T binding, and sedimentation coefficient of apoC-II. This contrasts with stoichiometric concentrations of α-crystallin required to suppress the amorphous aggregation of stressed proteins such as reduced α-lactalbumin. Two pieces of evidence suggest that α-crystallin directly interacts with amyloidogenic intermediates. First, sedimentation equilibrium and velocity experiments exclude high affinity interactions between α-crystallin and unstructured monomeric apoC-II. Second, the addition of α-crystallin does not lead to the accumulation of intermediate sized apoC-II species between monomer and large aggregates as indicated by gel filtration and sedimentation velocity experiments, suggesting that α-crystallin does not inhibit the relatively rapid fibril elongation upon nucleation. We propose that α-crystallin interacts stoichiometrically with partly structured amyloidogenic precursors, inhibiting amyloid formation at nucleation rather than the elongation phase. In doing so, α-crystallin forms transient complexes with apoC-II, in contrast to its chaperone behavior with stressed proteins.
Michael D. W. Griffin - One of the best experts on this subject based on the ideXlab platform.
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Apolipoprotein C-II Adopts Distinct Structures in Complex with Micellar and Submicellar Forms of the Amyloid-Inhibiting Lipid-Mimetic Dodecylphosphocholine.
Biophysical Journal, 2016Co-Authors: Timothy M. Ryan, Michael D. W. Griffin, Duncan J. Mcgillivray, Robert Knott, Kathleen Wood, Colin L. Masters, Nigel Kirby, Cyril C. CurtainAbstract:Abstract The formation of amyloid deposits is a common feature of a broad range of diseases, including atherosclerosis, Alzheimer's disease, and Parkinson's disease. The basis and role of amyloid deposition in the pathogenesis of these diseases is still being defined, however an interesting feature of amyloidogenic proteins is that the majority of the pathologically associated proteins are involved in lipid homeostasis, be it in lipid transport, incorporation into membranes, or the regulation of lipid pathways. Thus, amyloid-forming proteins commonly bind lipids, and lipids are generally involved in the proper folding of these proteins. However, understanding of the basis for these lipid-related aspects of amyloidogenesis is lacking. Thus, we have used the Apolipoprotein C-II amyloid model system in conjunction with x-ray and neutron scattering analyses to address this problem. Apolipoprotein C-II is a well-studied model system of systemic amyloid fibril formation, with a clear and well-defined pathway for fibril formation, where the effects of lipid interaction are characterized, particularly for the lipid mimetic dodecylphosphocholine. We show that the micellar state of an inhibitory lipid can have a very significant effect on protein conformation, with micelles stabilizing a particular α -helical structure, whereas submicellar lipids stabilize a very different dimeric, α -helical structure. These results indicate that lipids may have an important role in the development and progression of amyloid-related diseases.
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Charge and charge-pair mutations alter the rate of assembly and structural properties of Apolipoprotein C-II amyloid fibrils.
Biochemistry, 2015Co-Authors: Chai Lean Teoh, Geoffrey J. Howlett, Paul R. Gooley, Shuo Yang, Courtney O. Zlatic, Zachary Rosenes, Michael D. W. GriffinAbstract:The misfolding, aggregation, and accumulation of proteins as amyloid fibrils is a defining characteristic of several debilitating diseases. Human Apolipoprotein C-II (apoC-II) amyloid fibrils are representative of the fibrils formed by a number of plasma Apolipoproteins implicated in amyloid-related disease. Previous structural analyses identified a buried charge pair between residues K30 and D69 within apoC-II amyloid fibrils. We have investigated the effects of amino acid substitutions of these residues on apoC-II fibril formation. Two point mutations of apoC-II, D69K and K30D, as well as a reversed ion-pair mutant containing both mutations (KDDK) were generated. Fibril formation by the double mutant, apoC-II KDDK, and apoC-II D69K was enhanced compared to that of wild-type (WT) apoC-II, while apoC-II K30D lacked the ability to form fibrils under standard conditions. Structural analyses showed that WT apoC-II, apoC-II D69K, and apoC-II KDDK fibrils have similar secondary structures and morphologies. Siz...
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The Role of Lipid in Misfolding and Amyloid Fibril Formation by Apolipoprotein C-II
Advances in Experimental Medicine and Biology, 2015Co-Authors: Timothy M. Ryan, Geoffrey J. Howlett, Michael D. W. GriffinAbstract:Apolipoproteins are a key component of lipid transport in the circulatory system and share a number of structural features that facilitate this role. When bound to lipoprotein particles, these proteins are relatively stable. However, in the absence of lipids they display conformational instability and a propensity to aggregate into amyloid fibrils. Apolipoprotein C-II (apoC-II) is a member of the Apolipoprotein family that has been well characterised in terms of its misfolding and aggregation. In the absence of lipid, and at physiological ionic strength and pH, apoC-II readily forms amyloid fibrils with a twisted ribbon-like morphology that are amenable to a range of biophysical and structural analyses. Consistent with its lipid binding function, the misfolding and aggregation of apoC-II are substantially affected by the presence of lipid. Short-chain phospholipids at submicellar concentrations significantly accelerate amyloid formation by inducing a tetrameric form of apoC-II that can nucleate fibril aggregation. Conversely, phospholipid micelles and bilayers inhibit the formation of apoC-II ribbon-type fibrils, but induce slow formation of amyloid with a distinct straight fibril morphology. Our studies of the effects of lipid at each stage of amyloid formation, detailed in this chapter, have revealed complex behaviour dependent on the chemical nature of the lipid molecule, its association state, and the protein:lipid ratio.
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Avoiding the oligomeric state: αB-crystallin inhibits fragmentation and induces dissociation of Apolipoprotein C-II amyloid fibrils
The FASEB Journal, 2012Co-Authors: Katrina J. Binger, Geoffrey J. Howlett, John A. Carver, Heath Ecroyd, Shuo Yang, Michael D. W. GriffinAbstract:The in vivo aggregation of proteins into amyloid fibrils suggests that cellular mechanisms that normally prevent or reverse this aggregation have failed. The small heat-shock molecular chaperone protein αB-crystallin (αB-c) inhibits amyloid formation and colocalizes with amyloid plaques; however, the physiological reason for this localization remains unexplored. Here, using Apolipoprotein C-II (apoC-II) as a model fibril-forming system, we show that αB-c binds directly to mature amyloid fibrils (Kd 5.4 ± 0.5 μM). In doing so, αB-c stabilized the fibrils from dilution-induced fragmentation, halted elongation of partially formed fibrils, and promoted the dissociation of mature fibrils into soluble monomers. Moreover, in the absence of dilution, the association of αB-c with apoC-II fibrils induced a 14-fold increase in average aggregate size, resulting in large fibrillar tangles reminiscent of protein inclusions. We propose that the binding of αB-c to fibrils prevents fragmentation and mediates the lateral a...
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Shear Flow Induced Changes in Apolipoprotein C-II Conformation and Amyloid Fibril Formation
Biochemistry, 2011Co-Authors: Chai Lean Teoh, Innocent B. Bekard, Peter Asimakis, Michael D. W. Griffin, Timothy M. Ryan, Dave E. Dunstan, Geoffrey J. HowlettAbstract:The misfolding and self-assembly of proteins into amyloid fibrils that occur in several debilitating diseases are affected by a variety of environmental factors, including mechanical factors associated with shear flow. We examined the effects of shear flow on amyloid fibril formation by human Apolipoprotein C-II (apoC-II). Shear fields (150, 300, and 500 s–1) accelerated the rate of apoC-II fibril formation (1 mg/mL) approximately 5–10-fold. Fibrils produced at shear rates of 150 and 300 s–1 were similar to the twisted ribbon fibrils formed in the absence of shear, while at 500 s–1, tangled ropelike structures were observed. The mechanism of the shear-induced acceleration of amyloid fibril formation was investigated at low apoC-II concentrations (50 μg/mL) where fibril formation does not occur. Circular dichroism and tryptophan fluorescence indicated that shear induced an irreversible change in apoC-II secondary structure. Fluorescence resonance energy transfer experiments using the single tryptophan resi...
Paul R. Gooley - One of the best experts on this subject based on the ideXlab platform.
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Charge and charge-pair mutations alter the rate of assembly and structural properties of Apolipoprotein C-II amyloid fibrils.
Biochemistry, 2015Co-Authors: Chai Lean Teoh, Geoffrey J. Howlett, Paul R. Gooley, Shuo Yang, Courtney O. Zlatic, Zachary Rosenes, Michael D. W. GriffinAbstract:The misfolding, aggregation, and accumulation of proteins as amyloid fibrils is a defining characteristic of several debilitating diseases. Human Apolipoprotein C-II (apoC-II) amyloid fibrils are representative of the fibrils formed by a number of plasma Apolipoproteins implicated in amyloid-related disease. Previous structural analyses identified a buried charge pair between residues K30 and D69 within apoC-II amyloid fibrils. We have investigated the effects of amino acid substitutions of these residues on apoC-II fibril formation. Two point mutations of apoC-II, D69K and K30D, as well as a reversed ion-pair mutant containing both mutations (KDDK) were generated. Fibril formation by the double mutant, apoC-II KDDK, and apoC-II D69K was enhanced compared to that of wild-type (WT) apoC-II, while apoC-II K30D lacked the ability to form fibrils under standard conditions. Structural analyses showed that WT apoC-II, apoC-II D69K, and apoC-II KDDK fibrils have similar secondary structures and morphologies. Siz...
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The Structure and Interactions of Human Apolipoprotein C-II in Dodecyl Phosphocholine†,‡
Biochemistry, 2004Co-Authors: Christopher A. Macraild, Geoffrey J. Howlett, Paul R. GooleyAbstract:The structure of human Apolipoprotein C-II (apoC-II) in the presence of dodecyl phosphocholine (DPC) micelles has been investigated by NMR spectroscopy. The resulting structural information is compared to that available for apoC-II in the presence of sodium dodecyl sulfate, revealing a high level of overall similarity but several significant differences. These findings further our understandings of the structural basis for apoC-II function. The interactions of the protein with the detergent micelle are probed using intermolecular nuclear Overhauser effects (NOEs) and paramagnetic agents. These interactions are seen across almost the full length of apoC-II and show the periodicity expected for an amphipathic helix interacting with the amphipathic surface of the DPC micelle. Furthermore, we observe specific contacts between lysine residues of apoC-II and protons near the phosphate group of DPC, consistent with the predictions of the so-called “snorkel hypothesis” of the structural basis for the apolipoprote...
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NMR structure of human Apolipoprotein C-II in the presence of sodium dodecyl sulfate.
Biochemistry, 2001Co-Authors: Christopher A. Macraild, Danny M. Hatters, Geoffrey J. Howlett, Paul R. GooleyAbstract:The structure and protein-detergent interactions of Apolipoprotein C-II (apoC-II) in the presence of SDS micelles have been investigated using circular dichroism and heteronuclear NMR techniques applied to 15 N-labeled protein. Micellar SDS, a commonly used mimetic of the lipoprotein surface, inhibits the aggregation of apoC-II and induces a stable structure containing approximately 60% R-helix as determined by circular dichroism. NMR reveals the first 12 residues of apoC-II to be structurally heterogeneous and largely disordered, with the rest of the protein forming a predominantly helical structure. Three regions of helical conformation, residues 16-36, 50-56, and 63-77, are well-defined by NMR-derived constraints, with the intervening regions showing more loosely defined helical conformation. The structure of apoC- II is compared to that determined for other Apolipoproteins in a similar environment. Our results shed light on the lipid interactions of apoC-II and its mechanism of lipoprotein lipase activation. Apolipoprotein C-II (apoC-II) 1 is a 79 residue exchange- able Apolipoprotein that plays an essential role in plasma lipid transport and metabolism. ApoC-II is a protein cofactor for lipoprotein lipase (LpL), an enzyme that hydrolyzes tri- acylglycerol during the metabolic remodeling of chylomi- crons and very low-density lipoproteins (1, 2). As with the other exchangeable Apolipoproteins, apoC-II binds reversibly to the polar lipid surface of plasma lipoprotein particles in vivo and associates with a range of natural and synthetic lipid surfaces in vitro with a concomitant change in secondary structure (3). Analysis of this conformational change and amino acid sequence analysis of apoC-II and other exchange- able Apolipoproteins have led to the generally accepted hypothesis that exchangeable Apolipoproteins associate with lipid surfaces by means of amphipathic helical regions believed to be present in all members of the family (4). The results of a number of studies have localized the lipid binding activity of apoC-II to a region in the N-terminal half of the protein with a strongly amphipathic nature and possibly to a second smaller region at the C-terminus (5-7). Activation of LpL is believed to involve the capacity of apoC-II to bind LpL as a binary protein-protein complex and stabilize a ternary complex with the lipoprotein substrate by means of the apoC-II lipid binding regions (8). It has also been suggested that apoC-II binding might induce a change in LpL conformation which exposes the active site to substrate in a manner analogous to the interaction of pancreatic lipase with its protein cofactor, colipase ( 9). However, in the absence of detailed structural information on apoC-II and its interactions with lipid and LpL, the details of this model remain controversial. ApoC-II in lipid-free solution has long been known to self- associate, and recently this association was shown to result in the formation of amyloid-like fibrils (10). The presence of phospholipid surfaces or sodium dodecyl sulfate (SDS) micelles inhibits amyloid formation. It has been suggested that in the absence of lipid apoC-II adopts a less-ordered structure that is prone to conformational changes leading to amyloid formation, whereas the presence of lipid stabilizes R-helical conformations and protects against the formation of amyloid-like ‚-sheet structures (10). A number of other Apolipoproteins have been shown to form amyloid fibrils in vivo (11-13), and amyloid has been identified in athero- sclerotic plaques (14, 15). Structural detail of apoC-II in its lipid-bound form may provide valuable insight into the process of amyloid fibril formation by apoC-II and apoli- poproteins in general and might suggest mechanisms to prevent its occurrence in vivo. Previous structural studies of apoC-II have focused on
Mikihiko Kawano - One of the best experts on this subject based on the ideXlab platform.
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A case of Apolipoprotein C-II deficiency with coronary artery disease
Clinical and Experimental Medicine, 2002Co-Authors: Mikihiko Kawano, K. Kodama, Hidekuni Inadera, Yasushi Saito, M. Saito, Toshio Yaginuma, Yasunori Kanazawa, Masanobu KawakamiAbstract:A 56-year-old male with Apolipoprotein C-II deficiency experienced a myocardial infarction without pancreatitis. A coronary angigram showed complete occlusions of both the right and circumflex coronary arteries. His serum lipid levels were as follows: fasting total cholesterol 3.15 mmol/l; postprandial total cholesterol 3.62 mmol/l; fasting triglycerides 1.46 mmol/l; postprandial triglycerides 6.14 mmol/l; fasting high-density lipoprotein-cholesterol 0.47 mmol/l; and postprandial high-density lipoprotein cholesterol 0.36 mmol/l. His fasting level of plasma Apolipoprotein C-II was 0.0005 g/l, but his plasma levels of other Apolipoproteins were within normal ranges. A DNA sequence analysis of the Apolipoprotein C-II gene showed no mutations in exon 1, 2, 3, or 4, where most gene mutations related to Apolipoprotein C-II deficiency occur. We report this patient's very rare heterozygous Apolipoprotein C-II deficiency with coronary artery disease. Although this patient had some risk factors for coronary artery disease, coronary atherosclerosis in this patient might have occurred as a result of lipoprotein abnormalities caused by at least one mutation in the Apolipoprotein C-II gene.
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M. KawanoK. KodamaH. InaderaY. SaitoM. SaitoT. YaginumaY. KanazawaM. Kawakami A case of Apolipoprotein C-II deficiency with coronary artery disease
2002Co-Authors: Mikihiko KawanoAbstract:A 56-year-old male with Apolipoprotein C-II defi- ciency experienced a myocardial infarction without pancreati- tis. A coronary angiogram showed complete occlusions of both the right and circumflex coronary arteries. His serum lipid lev- els were as follows: fasting total cholesterol 3.15 mmol/l; post- prandial total cholesterol 3.62 mmol/l; fasting triglycerides 1.46 mmol/l; postprandial triglycerides 6.14 mmol/l; fasting high-density lipoprotein-cholesterol 0.47 mmol/l; and post- prandial high-density lipoprotein cholesterol 0.36 mmol/l. His fasting level of plasma Apolipoprotein C-II was 0.005 g/l, but his plasma levels of other Apolipoproteins were within normal ranges. A DNA sequence analysis of the Apolipoprotein C-II gene showed no mutations in exon 1, 2, 3, or 4, where most gene mutations related to Apolipoprotein C-II deficiency occur. We report this patient's very rare heterozygous Apolipoprotein C-II deficiency with coronary artery disease. Although this patient had some risk factors for coronary artery disease, coro- nary atherosclerosis in this patient might have occurred as a result of lipoprotein abnormalities caused by at least one muta- tion in the Apolipoprotein C-II gene.
