David Atkinson

Boston University | BU · Department of Physiology and Biophysics

Population studies have found that a natural human apoA-I variant, apoA-I[K107del], is strongly associated with low HDL-C but normal plasma apoA-I levels. We aimed to reveal properties of this variant that contribute to its unusual phenotype associated with atherosclerosis. Our oil-drop tensiometry studies revealed that compared to WT, recombinant...

ApoA-I and the ATP-binding cassette transporter A1 (ABCA1) play important roles in nascent HDL (nHDL) biogenesis, the first step in the pathway of reverse cholesterol transport that protects against cardiovascular disease. On the basis of the crystal structure of a C-terminally truncated form of apoA-IΔ;[185-243]) determined in our laboratory, we h...

ApoA-I activates LCAT that converts lipoprotein cholesterol to cholesteryl ester (CE). Molecular dynamic simulations suggested earlier that helices 5 of two antiparallel apoA-I molecules on discoidal HDL form an amphipathic tunnel for migration of acyl chains and unesterified cholesterol to the active sites of LCAT. Our recent crystal structure of...

Apolipoprotein (apo)A-I is an organizing scaffold protein that is critical to high-density lipoprotein (HDL) structure and metabolism, probably mediating many of its cardioprotective properties. However, HDL biogenesis is poorly understood, as lipid-free apoA-I has been notoriously resistant to high-resolution structural study. Published models fro...

Hypertriglyceridemia (HTG) is an independent factor of atherosclerotic cardiovascular disease and a hallmark of many metabolic disorders. However, the molecular etiology of HTG is still largely unknown. In mice, severe HTG may be induced by expression of specific mutants of apolipoprotein (apo) A-I or wild type (WT) apoE4. Expression of a certain a...

Apolipoprotein A-I (apoA-I) plays important structural and functional roles in reverse cholesterol transport. We have described the molecular structure of the N-terminal domain, Δ(185-243) by x-ray crystallography. To understand the role of the C-terminal domain, constructs with sequential elongation of Δ(185-243), by increments of 11-residue seque...

Apolipoprotein A-I is the major protein in high-density lipoprotein (HDL) and plays an important role during the process of reverse cholesterol transport (RCT). Knowledge of the high-resolution structure of full-length apoA-I is vital for a molecular understanding of the function of HDL at the various steps of the RCT pathway. Due to the flexible n...

We found earlier that apolipoprotein A-I (apoA-I) variants that induced hypertriglyceridemia (HTG) in mice had increased affinity to triglyceride (TG)-rich lipoproteins and thereby impaired their catabolism. Here, we tested if a naturally occurring human apoA-I mutation, Lys107del, associated with HTG also promotes apoA-I binding to TG-rich particl...

High-density lipoproteins (HDLs) and their major protein, apoA-I, remove excess cellular cholesterol and protect against atherosclerosis. However, in acquired amyloidosis, non-variant full-length apoA-I deposits as fibrils in atherosclerotic plaques; in familial amyloidosis, N-terminal fragments of variant apoA-I deposit in vital organs damaging th...

Apolipoprotein A-I (apoA-I) has a great conformational flexibility to exist in lipid free, lipid poor and lipid bound states during lipid metabolism. To address the lipid binding and the dynamic desorption behavior of apoA-I at lipoprotein surfaces, apoA-I, Δ(185-243)apoA-I and Δ(1-59)(185-243)apoA-I were studied at triolein/water and phosphatidylc...

HDL remove cell cholesterol and protects against atherosclerosis. Apolipoprotein A-I provides a flexible structural scaffold and an important functional ligand on the HDL surface. We propose structural models for apoA-IMilano (R173C) and apoA-IParis (R151) mutants that show high cardioprotection despite low HDL levels. Previous studies established...

Thermal and stability properties of B17, the 17 % N-terminal domain of apo B, were carried out using differential scanning calorimetry spectroscopy, where the thermal characteristics of the polypeptide were studied and analyzed. The heat capacity data of B17 showed that the protein undergoes two transitions between 50 and 90 °C, with T m’s at 65.9...

Objectives Heart disease remains the leading cause of death for both women and men in the USA. High blood pressure and elevated plasma cholesterol are two main risk factors for heart disease and lead to atherosclerosis. Plasma levels of high-density lipoproteins, HDL, are negatively correlated with the incidence of atherosclerosis and the mechanism...

Structural characterization of B17, the 17% N-terminal domain of apo B, was carried out using circular dichroic (CD) spectroscopy, where secondary and tertiary structures were studied as a function of temperature and pH. Mild acidic conditions that correlate with histidine protonation invoked a change in the α-helix and random coil contents of the...

Apolipoprotein A-I (apoA-I) is the main protein of plasma high-density lipoproteins (HDL, or good cholesterol) that remove excess cell cholesterol and protect against atherosclerosis. In hereditary amyloidosis, mutations in apoA-I promote its proteolysis and the deposition of the 9-11 kDa N-terminal fragments as fibrils in vital organs such as kidn...

Lipoproteins are water-soluble non-covalent assemblies comprised of several proteins (termed apolipoproteins) and several hundred lipid molecules. These assemblies mediate transport and metabolism of lipids and are central to the development of major human diseases, most notably atherosclerosis. Plasma lipoproteins are divided into classes accordin...

Apolipoprotein A-I (apoA-I) plays important structural and functional roles in plasma high density lipoprotein (HDL) that is responsible for reverse cholesterol transport. However, a molecular understanding of HDL assembly and function remains enigmatic. The 2.2-Å crystal structure of Δ(185–243)apoA-I reported here shows that it forms a half-circle...

A single copy of apoB is the sole protein component of human LDL. ApoB is crucial for LDL particle stabilization and is the ligand for LDL receptor, through which cholesterol is delivered to cells. Dysregulation of the pathways of LDL metabolism is well documented in the pathophysiology of atherosclerosis. However, an understanding of the structure...

Hypertriglyceridemia (HTG) is a common lipid abnormality in humans. However, its etiology remains largely unknown. It was shown that severe HTG can be induced in mice by overexpression of wild-type (WT) apolipoprotein E (apoE) or specific apoA-I mutants. Certain mutations in apoE4 were found to affect plasma triglyceride (TG) levels in mice overexp...

Apolipoprotein B-100 (apo B) is the sole protein component of normal human low density lipoprotein (LDL). Elevated levels of LDL have been correlated with atherosclerosis and other coronary artery diseases. The large size of apo B (4536 aa) necessitates that it be studied in pieces corresponding to its structurally organized domains. The 17% N-term...

Human LDL undergoes a reversible thermal order-disorder phase transition associated with the cholesterol ester packing in the lipid core. Structural changes associated with this phase transition have been shown to affect the resistance of LDL to oxidation in vitro studies. Previous electron cryo-microscopy studies have provided image evidence that...

A 26 Å resolution map of the structure of human low-density lipoprotein (LDL) was obtained from electron cryomicroscopy and single-particle image reconstruction. The structure showed a discoidal-shaped LDL particle with high-density regions mainly distributed at the edge of the particle and low-density regions at the flat surface that covers the co...

The synthesis of apolipoprotein B (apoB) dictates the formation of chylomicrons and very low-density lipoproteins, two major lipoprotein precursors in the human plasma. Despite its biological significance, the mechanism of the assembly of these apoB-containing lipoproteins remains elusive. An essential obstacle is the lack of systems that allow fin...

In humans and animal models, high plasma concentrations of apolipoprotein (apo) E are associated with hypertriglyceridemia. It has been shown that overexpression of human wild-type (WT) apoE4 in apoE-deficient mice induces hypertriglyceridemia. In contrast, overexpression of an apoE4 variant, apoE4-mut1 (apoE4(L261A, W264A, F265A, L268A, V269A)), d...

Apolipoprotein A-I (apoA-I), the major protein of high-density lipoprotein (HDL), moves between HDL and triacylglycerol-rich lipoproteins during metabolism. We reported that apoA-I is conformationally flexible at the triolein/water (TO/W) interface, partially desorbing at low surface pressure (Pi) but totally desorbing at Pi > 19 mN/m. We now repor...

Human apolipoprotein A-I (apoA-I) is the principle apolipoprotein of high-density lipoproteins that are critically involved in reverse cholesterol transport. The intrinsically flexibility of apoA-I has hindered studies of the structural and functional details of the protein. Our strategy is to study peptide models representing different regions of...

To identify residues and segments in the central region of apolipoprotein A-I (apoA-I) that are important for the protein structure and stability, we studied the effects of four double charge ablations, D102A/D103A, E110A/E111A, R116V/K118A, and R160V/H162A, and two deletion mutations, Delta(61-78) and Delta(121-142), on the conformation and stabil...

Apolipoprotein A-I (apoA-I) is the major protein in high density lipoprotein (HDL). During lipid metabolism, apoA-I moves among HDL and triacylglycerol-rich lipoproteins. The main structure and the major lipid binding motif of apoA-I is the amphipathic alpha-helix. To understand how apoA-I behaves at hydrophobic lipoprotein interfaces, the interfac...

Because of its role in reverse cholesterol transport, human apolipoprotein A-I is the most widely studied exchangeable apolipoprotein. Residues 1-43 of human apoA-I, encoded by exon 3 of the gene, are highly conserved and less well understood than residues 44-243, encoded by exon 4. In contrast to residues 44-243, residues 1-43 do not contain the 2...

Apolipoprotein A-I (apoA-I, 243 amino acids) is the major protein of high-density lipoproteins (HDL) that plays an important structural and functional role in lipid transport and metabolism. The central region of apoA-I (residues 60-183) is predicted to contain exclusively amphipathic alpha-helices formed from tandem 22-mer sequence repeats. To ana...

Amphipathic alpha-helices are the main structure and the major lipid binding motif of exchangeable apolipoproteins. To understand how these apolipoproteins behave at an hydrophobic lipoprotein interface, the interfacial properties of a consensus sequence peptide (CSP) derived from three exchangeable apolipoproteins (A-I, A-IV, and E) were studied u...

Apolipoprotein A-I (apoA-I) plays an important structural and functional role in lipid transport and metabolism. This work is focused on the central region of apoA-I (residues 60-183) that is predicted to contain exclusively amphipathic alpha-helices. Six N- and/or C-terminally truncated mutants, delta(1-41), delta(1-59), delta(198-243), delta(209-...

To probe the structure and stability of the central region of lipid-free apolipoprotein (apo) A-I (residues 123-165), we studied the effects of four mutations made in this region on the conformation, stability, dimyristoylphosphatidylcholine (DMPC) binding kinetics, and size of discoidal reconstituted high-density lipoprotein (rHDL) particles. The...

To probe the secondary structure of the C-terminus (residues 165-243) of lipid-free human apolipoprotein A-I (apoA-I) and its role in protein stability, recombinant wild-type and seven site-specific mutants have been produced in C127 cells, purified, and studied by circular dichroism and fluorescence spectroscopy. A double substitution (G185P, G186...

Thermal and chemical unfolding of lipid-free apolipoprotein C-1 (apoC-1), a 6-kDa protein component of very low density and high-density lipoproteins, was analyzed by far-UV CD. In neutral 1 mM Na2HPO4 solutions containing 6-7 micrograms/mL protein, the apoC-1 monomer is approximately 30% alpha-helical at 0-22 degrees C and unfolds reversibly from...

Human plasma apolipoprotein A-2 (apoA-2) is the second major protein of the high-density lipoproteins that mediate the transport and metabolism of cholesterol. Using CD spectroscopy and differential scanning calorimetry, we demonstrate that the structure of lipid-free apoA-2 in neutral low-salt solutions is most stable at approximately 25 degrees C...

Apolipoprotein A-1 (apoA-1) in complex with high-density lipoprotein is critically involved in the transport and metabolism of cholesterol and in the pathogenesis of atherosclerosis. We reexamined the thermal unfolding of lipid-free apoA-1 in low-salt solution at pH approximately 7, by using differential scanning calorimetry and circular dichroism....

In this report, images of low density lipoprotein (LDL) in vitreous ice at approximately 30 A resolution are presented. These images show that LDL is a quasi-spherical particle, approximately 220-240 A in diameter, with a region of low density (lipid) surrounded by a ring (in projection) of high density believed to represent apolipoprotein B-100. T...

The primary and secondary structure of human plasma apolipoprotein A-I and apolipoprotein E-3 have been analyzed to further our understanding of the secondary and tertiary conformation of these proteins and the structure and function of plasma lipoprotein particles. The methods used to analyze the primary sequence of these proteins used computer pr...

The past year has seen significant advances in understanding the detailed molecular features of the plasma lipoprotein apoproteins responsible of lipid binding and function. These advances have been made through a combination of model building, the mapping of epitopes to monoclonal antibodies and X-ray crystallographic structure determination.

The polymorphic behavior and molecular packing in different polymorphic forms of stereospecific triacylglycerols, 1,2-dipalmitoyl-3-lauroyl-sn-glycerol (PP12) and 1,2-dipalmitoyl-3-myristoyl-sn-glycerol (PP14) were examined by X-ray diffraction, differential scanning calorimetry, infrared and Raman spectroscopy techniques. The molecular packing and...

The unfolding of human apolipoprotein B-100 in its native lipid environment, low density lipoprotein (LDL), and in a soluble, lipid-free complex with sodium deoxycholate (NaDC) has been examined using differential scanning calorimetry (DSC) and near UV circular dichroic (CD) spectroscopy. High resolution DSC shows that LDL undergoes three thermal t...

As models for the effects of unesterified cholesterol (UC) on the lipid organization of low density lipoprotein (LDL), microemulsions containing either egg yolk phosphatidylcholine (EYPC) or dimyristoyl phosphatidylcholine (DMPC) as the surface component, cholesteryl oleate (CO) as the core component, and varying amounts of unesterified cholesterol...

The molecular packing in different polymorphic forms of a stereospecific triacylglycerol, 1,2-dipalmitoyl-3-decanoyl-sn-glycerol (PP10), was examined by X-ray diffraction, differential scanning calorimetry, and infrared and Raman spectroscopy techniques. On quenching, the isotropic liquid produced a hexagonally packed α-phase, which upon heating me...

The molecular packing in triacylglycerols having different acyl chains has been examined by differential scanning calorimetry, powder X-ray diffraction and vibrational spectroscopy (infrared and Raman) techniques. In the triacylglycerols examined, the acyl chain length, unsaturation or the position of substitution on the glycerol were changed syste...

The current knowledge of the primary structures of apolipoproteins (ApoLP’s) is impressive. Traditional protein sequencing technology has provided the primary amino acid sequences of the major exchangeable apo-LP’s - ApoAI, All, the C’s and E (1-4). Recently, simultaneously in several laboratories, the complete amino acid sequence of ApoBl00 has be...

The polymorphic behavior of symmetric diacid triacylglycerols (TGs), 1,3-dioleoyl-2-stearoyl (OSO), 2-elaidoyl (OEO), and 2-vaccinoyl (OVO) glycerols were studied by differential scanning colorimetry (DSC) and X-ray diffraction and compared with the corresponding monoacid TGs triolein (OOO), tristearin (SSS), trielaidin (EEE), and trivaccinin (VVV)...

Particles closely resembling rat high density lipoproteins (HDL) in terms of equilibrium density profile and particle size were prepared by sonication of apoA-I with a microemulsion made with egg lecithin and cholesterol oleate. These particles, like authentic HDL, allowed selective uptake of their cholesterol ester moieties by cultured cells witho...

A series of N-acyl sphingomyelins (C16:0, C18:0, C20:0, C22:0, and C24:0) have been synthesized and single bilayer vesicles formed by sonication and ultracentrifugation. X-ray scattering data have been collected from the sphingomyelin vesicles at 50 degrees C in the melted-chain state. The x-ray scattering data have been transformed to the correspo...

We have isolated and sequenced overlapping cDNA clones covering the entire sequence of human apolipoprotein B-100 (apoB-100). DNA sequence analysis and determination of the mRNA transcription initiation site by S1 nuclease mapping showed that the apoB mRNA consists of 14,112 nucleotides including the 5' and 3' untranslated regions which are 128 and...

The physical properties in water of a series of 1:1 acid-soap compounds formed from fatty acids and potassium soaps with saturated (10-18 carbons) and omega-9 monounsaturated (18 carbons) hydrocarbon chains have been studied by using differential scanning calorimetry (DSC), X-ray diffraction, and direct and polarized light microscopy. DSC showed th...

Apoprotein B, the major apoprotein of normal human low density lipoprotein (LDL) was solubilized with sodium deoxycholate (NaDC). The protein was recombined with the phospholipid dimyristoyl phosphatidylcholine (DMPC) to produce a complex of DMPC-apoB (4:1 w/w). Carboxyfluorescein and [3H]dextran entrapment studies show the DMPC-apoB 4:1 (w/w) comp...

The methodologies described here for the selective and sequential reassembly of model LDL particles, although in many instances still in the developmental stages, will undoubtedly provide a basis on which further advances in LDL reassembly will be made. Reassembled LDL complexes of defined lipids and apoB provide well-defined model systems in which...

Triacylglycerols, which usually contain at least one unsaturated fatty acid, are the most important forms of stored biological lipids in teleosts, mammals, and most plants. Since the physical properties of such mixed-chain triacylglycerols are poorly understood, a systematic study of such compounds has been initiated. Stereospecific 1,2-dioleoyl-3-...

3-Acyl-sn-glycerols with even-numbered saturated fatty acyl chains from decanoate to lignocerate were synthesized. Successful hydrolysis of the long acyl chain intermediate 1,2-isopropylidene-3-acyl-sn-glycerols from stearate to lignocerate was accomplished by applying the compounds to silica gel and exposing them to hydrogen chloride gas at -75 de...

Reassembled low density lipoprotein (LDL) complexes have been prepared by the interaction of lipid-free sodium deoxycholate-solubilized apoprotein B (apoB) of native human LDL with preformed, 200 A in diameter, microemulsions of cholesteryl oleate (CO), surface-stabilized by either egg yolk phosphatidylcholine ( EYPC ) or dimyristoyl phosphatidylch...

Stereospecific 1,2-dipalmitoyl-sn-glycerol and 1,2-dipalmitoyl-3-acyl-sn-glycerols with even-carbon saturated fatty acyl chains of 2–16 carbons in length were synthesized. The polymorphic behavior and packing arrangements of the most stable crystal form obtained, from the solvent of crystallization, were studied by differential scanning calorimetry...

These studies with neutron small-angle scattering were designed to probe the location of the apoprotein of HDL on recombinant particles formed with phospholipids. The use of isotopic substitution with deuterium in the headgroup of the phospholipid allows the positions of the molecular components to be probed in more detail. These initial experiment...

Cholesteryl esters, the intracellular storage form and intravascular transport form of cholesterol, can exist in crystal, liquid crystal and liquid states. The physical state of cholesteryl esters at physiologic temperatures may be a determinant of their pathogenicity. This review has surveyed saturated aliphatic cholesteryl esters of chain length...

Apoprotein B (apoB) of human plasma low-density lipoprotein (LDL) (d 1.025-1.050 g/mL) has been solubilized with solid sodium deoxycholate (NaDC) above its critical micellar concentration. ApoB is isolated by gel-filtration chromatography as a mixed micellar complex of protein and detergent in high yield in a lipid-free form. A soluble apoB-dimyris...

Nine even-numbered saturated (C4 to C20) and two unsaturated (C18:1, C18:2) cholesterol alkyl ethers were studied by differential scanning calorimetry, polarizing microscopy, and X-ray powder diffraction. Seven of the nine saturated ethers examined melt into stable liquid crystal mesophases. Mesophase transition temperatures vary over a much narrow...

At body temperature the stable form of triglycerides rich in saturated fatty acids is crystalline. We examined the physical state of triglyceride-rich lymph lipoproteins from rats fed saturated fat, as a function of temperature. When chylomicrons and very low density lipoproteins were collected, isolated, and examined at 37 degrees C, they were liq...

Differential scanning calorimetry (DSC) and x-ray diffraction studies were performed on chylomicrons and very low density lipoproteins (VLDL), from nonhuman primates fed saturated fat, isolated from lymph at two different temperatures (15 and 39 degrees C). When heated from -10 leads to 60 degrees C, chylomicrons and VLDL isolated at 15 degrees C h...

Differential scanning calorimetry and X-ray diffraction of anhydrous and hydrated N-palmitoylgalactosylsphingosine (NPGS) show evidence of complex polymorphic behavior and interconversions between stable and metastable structural forms. Anhydrous NPGS exhibits three lamellar crystal forms (A, B, and B') at temperatures below 143 degrees C and a liq...

The conformation of β-casein A in the monomeric and thermally aggregated states has been investigated by a range of techniques. β-Casein exists as a monomer in solution at 4°C and at concentrations up to at least 3 g/dl. The molecule is flexible and exhibits a lot of segmental motion, but its secondary structure is not wholly random coil; about one...

Cynomolgus monkeys, Macaca fascicularis, fed cholesterol-containing saturated-fat diets develop increased levels of high molecular weight plasma low density lipoproteins (LDL), associated with accelerated atherosclerosis. To study the composition and structure of these abnormal particles, LDL from monkeys, fed atherogenic and control diets, were ch...