The refined structure of nascent HDL reveals a key functional domain for particle maturation and dysfunction

Wu, Zhiyong; Wagner, Matthew A.; Zheng, Lemin; Parks, John S.; Shy, Jacinto M.; Smith, Jonathan; Gogonea, Valentin; Hazen, Stanley L.

doi:10.1038/nsmb1284

Cited by 190 publications

(350 citation statements)

References 42 publications

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“…Notably, although the acyl chain dynamics are modified by cholesterol, 31 P NMR spectroscopy shows that the phosphate found in the lipid head group appears to have the same dynamic properties, regardless of the presence of cholesterol (Figure S2 A in the Supporting Information). This is in agreement with the recently solved 3D structure of HDL particles, in which amphipathic helices surround the lipid disc around the acyl chains and no direct contacts are observed with phospholipid head groups 5, 20, 45…”

Section: Resultssupporting

confidence: 92%

Lipid Internal Dynamics Probed in Nanodiscs

et al. 2017

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Nanodiscs offer a very promising tool to incorporate membrane proteins into native‐like lipid bilayers and an alternative to liposomes to maintain protein functions and protein–lipid interactions in a soluble nanoscale object. The activity of the incorporated membrane protein appears to be correlated to its dynamics in the lipid bilayer and by protein–lipid interactions. These two parameters depend on the lipid internal dynamics surrounded by the lipid‐encircling discoidal scaffold protein that might differ from more unrestricted lipid bilayers observed in vesicles or cellular extracts. A solid‐state NMR spectroscopy investigation of lipid internal dynamics and thermotropism in nanodiscs is reported. The gel‐to‐fluid phase transition is almost abolished for nanodiscs, which maintain lipid fluid properties for a large temperature range. The addition of cholesterol allows fine‐tuning of the internal bilayer dynamics by increasing chain ordering. Increased site‐specific order parameters along the acyl chain reflect a higher internal ordering in nanodiscs compared with liposomes at room temperature; this is induced by the scaffold protein, which restricts lipid diffusion in the nanodisc area.

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Section: Resultssupporting

confidence: 92%

Lipid Internal Dynamics Probed in Nanodiscs

et al. 2017

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“…Relevant to model iii, Shih et al (38) recently published both all-atom and coarse-grained MD simulations of the solar flare model (37). After their simulations, the protruding solar flare loops (residues 159 -180) in both the original solar flare model and the corrected model collapsed, and the salt bridges proposed to stabilize the solar flares broke.…”

Section: Discussionmentioning

confidence: 99%

“…The essential first step in development of the DSH model was the fitting of SANS data collected from deuterated apoA-I nascent HDL to the following three models: (i) low resolution protein and lipid shapes of the DSH model, (ii) a double helical belt model, and (iii) the solar flare model that is essentially a double helical belt model containing symmetrical segments (residues 159 -180) detached from the disc edge (37). The three models were fitted to the SANS scattering intensity for protein (contrast matched to protein to test the coil shape of the DSH protein) or the SANS scattering intensity for lipid (contrast matched to lipid to test the prolate ellipsoidal shape of the DSH lipid).…”

Section: Discussionmentioning

confidence: 99%

Assessment of the Validity of the Double Superhelix Model for Reconstituted High Density Lipoproteins

Jones

Zhang

Catte

et al. 2010

Journal of Biological Chemistry

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High density lipoproteins (HDL) represent a heterogeneous population of particles with apoA-I as the major protein (1). Whether apoA-I/HDL 2 plays a direct role in cardiovascular disease prevention (e.g. removal of cholesterol from clogged arteries) or an indirect one (e.g. acts as a platform for the clustering of protective molecules, such as anti-inflammatory or antioxidant proteins), detailed knowledge of HDL structure is a key to understanding the molecular mechanism underlying these processes. Because the conformation of apoA-I on HDL is highly plastic (1), understanding apoA-I/HDL structure and dynamics is not straightforward.Since the early 1970s, the standard model for HDL particles reconstituted from apolipoprotein A-I (apoA-I) and phospholipid (apoA-I/HDL) has been that of a discoidal particle on the order of 100 Å in diameter and the thickness of a phospholipid bilayer. The initial observation of discoidal HDL particles was made by Forte et al. (2) when they examined HDL from patients with familial lecithin:cholesterol acyltransferase deficiency by negative stain EM. Reconstituted apoA-I/HDL particles (3) and nascent HDL from lymph (4) were then observed by negative stain EM to also have a discoidal shape. X-ray and neutron scattering studies (5, 6) provided further support for the standard discoidal model. The standard discoidal model has been used to interpret the results of a large number of experimental studies of the structure of reconstituted apoA-I/HDL particles. For review, see however, Wu et al. (11) used small angle neutron scattering to develop a model for apoA-I/HDL particles that is dramatically different from the standard model. In their model, termed a double superhelix (DSH), apoA-I possesses an open helical shape that twists around a central prolate ellipsoidal particle resembling a partial type I hexagonal lyotropic liquid crystalline phase.The DSH model is interesting. It is similar to MD simulation-based models (12) in that the proposed double superhelix forms a left-handed spiral as it wraps around the prolate ellip-

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“…Lipid-free apoA-I binds to the ABCA1 dimer (3). Lipids are loaded onto apoA-I, and the ABCA1 dimer dissociates into monomers (4). Lipidated apoA-I spontaneously binds to the PM and is in equilibrium between the PM and the media (5).…”

Section: Methodsmentioning

confidence: 99%

ABCA1 dimer–monomer interconversion during HDL generation revealed by single-molecule imaging

Nagata

Nakada

Kasai

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The generation of high-density lipoprotein (HDL), one of the most critical events for preventing atherosclerosis, is mediated by ATPbinding cassette protein A1 (ABCA1). ABCA1 is known to transfer cellular cholesterol and phospholipids to apolipoprotein A-I (apoA-I) for generating discoidal HDL (dHDL) particles, composed of 100-200 lipid molecules surrounded by two apoA-I molecules; however, the regulatory mechanisms are still poorly understood. Here we observed ABCA1-GFP and apoA-I at the level of single molecules on the plasma membrane via a total internal reflection fluorescence microscope. We found that about 70% of total ABCA1-GFP spots are immobilized on the plasma membrane and estimated that about 89% of immobile ABCA1 molecules are in dimers. Furthermore, an ATPase-deficient ABCA1 mutant failed to be immobilized or form a dimer. We found that the lipid acceptor apoA-I interacts with the ABCA1 dimer to generate dHDL and is followed by ABCA1 dimermonomer interconversion. This indicates that the formation of the ABCA1 dimer is the key for apoA-I binding and nascent HDL generation. Our findings suggest the physiological significance of conversion of the ABCA1 monomer to a dimer: The dimer serves as a receptor for two apoA-I molecules for dHDL particle generation.membrane protein | transporter P lasma high-density lipoprotein (HDL) is critical for preventing coronary artery disease (1). A member of the ATPdependent transporter family of ABC proteins, ATP-binding cassette protein A1 (ABCA1) initiates the generation of discoidal HDL (dHDL), a bilayer fragment consisting of 100-200 lipids wrapped by two molecules of apolipoprotein A-I (apoA-I) (2-4), by exporting cholesterol and phospholipids to lipid-free apoA-I in serum (5). More than 70 mutations have been identified in the ABCA1 gene. Indeed, mutations in ABCA1 lead to Tangier disease, which is characterized by plasma HDL deficiency (6-10). ABCA1 has two large extracellular domains (ECDs), and the two intramolecular disulfide bonds between them are necessary for apoA-I binding and HDL formation (11-13) (Fig. 1A). Two pieces of evidence suggest that apoA-I interacts with a specific conformation of the ECDs in an ATP-dependent manner: Chemical cross-linkers can cross-link apoA-I with ABCA1, and ATPasedeficient ABCA1 mutants fail to mediate apoA-I binding and crosslinking. However, the importance of direct binding of ABCA1-apoA-I in HDL formation is still controversial and, furthermore, how a dHDL particle containing two molecules of apoA-I is formed from lipid-free apoA-I monomers and membrane lipids is unknown.To address these issues, we performed single-molecule fluorescence imaging (14, 15) of ABCA1 and apoA-I on the plasma membrane (PM) via a total internal reflection fluorescence (TIRF) microscope in living cells. We examined the dynamic behaviors of ABCA1 as well as the interaction of ABCA1 with apoA-I, and found that ABCA1 forms an immobile dimer on the PM; the ABCA1 dimer then dissociates into diffusing monomers upon interaction with apoA-I, finally gen...

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The refined structure of nascent HDL reveals a key functional domain for particle maturation and dysfunction

Cited by 190 publications

References 42 publications

Lipid Internal Dynamics Probed in Nanodiscs

Lipid Internal Dynamics Probed in Nanodiscs

Assessment of the Validity of the Double Superhelix Model for Reconstituted High Density Lipoproteins

ABCA1 dimer–monomer interconversion during HDL generation revealed by single-molecule imaging

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