Assembly of Lipoprotein Particles Containing Apolipoprotein-B: Structural Model for the Nascent Lipoprotein Particle

Richardson, Patricia A.; Manchekar, Medha; Dashti, Nassrin; Jones, Martin K.; Beigneux, Anne P.; Young, Stephen G.; Harvey, Stephen C.; Segrest, Jere P.

doi:10.1529/biophysj.104.046235

Cited by 70 publications

(122 citation statements)

References 47 publications

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“…We propose that the initiation complex in the assembly of apoB-containing lipoprotein particle is PL-rich suggesting a small bilayer type organization rather than a TAG-rich emulsion proposed by others (32). Although our results (27,28) demonstrated that MTP is not a structural requirement for the formation of the lipid pocket, they did not rule out its potential functional role, i.e. transfer of lipids to the nascent apoB:1000, in this process.…”

Section: * This Work Was Supported By the National Institutes Of Healcontrasting

confidence: 62%

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Microsomal Triglyceride Transfer Protein Activity Is Not Required for the Initiation of Apolipoprotein B-containing Lipoprotein Assembly in McA-RH7777 Cells

Dashti

Manchekar

Sun

et al. 2007

Journal of Biological Chemistry

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We previously demonstrated that the N-terminal 1000 amino acid residues of human apolipoprotein (apo) B (designated apoB:1000) are competent to fold into a three-sided lipovitellin-like lipid binding cavity to form the apoB "lipid pocket" without a structural requirement for microsomal triglyceride transfer protein (MTP). Our results established that this primordial apoB-containing particle is phospholipid-rich (Manchekar, M., Richardson, P. E., Forte, T. M., Datta, G., Segrest, J. P., and Dashti, N. Apolipoprotein B (apoB)2 is synthesized primarily in hepatocytes and enterocytes and has a fundamental role in the transport and metabolism of plasma triacylglycerols (TAG) and cholesterol (1, 2). ApoB is a predominant protein component of very low density lipoproteins (VLDL) and intermediate density lipoproteins and is essentially the only apoprotein component of low density lipoproteins (LDL 2 ) (3, 4). ApoB100 (the fulllength protein) is one of the largest monomeric proteins known with 4536 amino acid residues (2). It is expressed primarily in mammalian liver, is an essential structural component for the formation and secretion of VLDL, and serves as a ligand for the LDL receptor (2). ApoB is present as a single molecule per lipoprotein particle (5); and therefore, its concentration in the plasma approximates the number of potential atherogenic lipoprotein particles.The processes involved in the assembly of apoB-containing lipoproteins in the liver are complex and are regulated at multiple levels throughout the secretory pathway. The assembly of apoB-containing lipoproteins occurs co-translationally (1), i.e. while the C-terminal portion is still being synthesized on the ribosome of the endoplasmic reticulum (ER), the N-terminal portion is translocated across the ER and is assembled as a small lipoprotein particle. The addition of lipids to apoB is widely believed to occur in two steps (2, 6, 7). The first step involves the addition of small amounts of lipids to apoB, as it is translated and translocated into the lumen of ER preventing its degradation and formation of a partially lipidated small pre-VLDL particle in the high density lipoprotein (HDL) density range (2,7,8). In the second step, this pre-VLDL particle is believed to acquire the bulk of its core lipids and is converted to bona fide VLDL (2, 7, 9), presumably by fusing with a large, VLDL-sized, apoB-free TAG particle (9). Biochemical studies of VLDL assembly support the concept that the bulk of neutral lipids are added in the second step after apoB translation is completed (10).* This work was supported by the National Institutes of Health Grants HL084685 and PO1 HL34343. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. 2 The abbreviations used are: apoB, apolipoprotein B; apoB:1000, N-terminal 22.05% (residues 1-1000) of the mature protein; BSA, bovine serum albu-

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Section: * This Work Was Supported By the National Institutes Of Healcontrasting

confidence: 62%

“…This experimentally derived observation was supported by our all atom molecular model for apoB:1000 (28). In this study, we examined the putative functional role of MTP in the initial lipidation of nascent apoB:1000 and initiation of apoB assembly in stable transformants of McA-RH cells.…”

Section: Mtp Inhibitors Have No Effect On the Secretion Or Cellular Amentioning

confidence: 65%

Microsomal Triglyceride Transfer Protein Activity Is Not Required for the Initiation of Apolipoprotein B-containing Lipoprotein Assembly in McA-RH7777 Cells

Dashti

Manchekar

Sun

et al. 2007

Journal of Biological Chemistry

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“…with the observation that the N-terminal ∼20% of apoB is homologous to a globular protein, lipovitellin (9,10). Lipovitellin is a nutrient storage protein in the egg yolk derived from vitellogenesis (11).…”

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confidence: 98%

Defining Lipid-Interacting Domains in the N-Terminal Region of Apolipoprotein B

et al. 2006

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Apolipoprotein B (ApoB) is a nonexchangeable apolipoprotein that dictates the synthesis of chylomicrons and very low density lipoproteins. ApoB is the major protein in low density lipoprotein, also known as the "bad cholesterol" that is directly implicated in atherosclerosis. It has been suggested that the N-terminal domain of apoB plays a critical role in the formation of apoB-containing lipoproteins through the initial recruitment of phospholipids in the endoplasmic reticulum. However, very little is known about the mechanism of lipoprotein nucleation by apoB. Here we demonstrate that a strong phospholipid remodeling function is associated with the predicted α-helical and C-sheet domains in the N-terminal 17% of apoB (B17). Using dimyristoylphosphatidylcholine (DMPC) as a model lipid, these domains can convert multilamellar DMPC vesicles into discoidal-shaped particles. The nascent particles reconstituted from different apoB domains are distinctive and compositionally homogenous. This phospholipid remodeling activity is also observed with egg phosphatidylcholine (egg PC) and is therefore not DMPC dependent. Using kinetic analysis of the DMPC clearance assay, we show that the identified phospholipid binding sequences all map to the surface of the lipid binding pocket in the B17 model based on the homologous protein, lipovitellin. Since both B17 and microsomal triglyceride transfer protein (MTP), a critical chaperone during lipoprotein assembly, are homologous to lipovitellin, the identification of these phospholipid remodeling sequences in B17 provides important insights into the potential mechanism that initiates the assembly of apoB-containing lipoproteins.Apolipoprotein B (apoB) is the only known nonexchangeable apolipoprotein in humans. It is the major protein component of low density lipoprotein (LDL), a major risk factor for atherosclerosis. Two forms of apoB are synthesized in humans, B48 from in small intestine and B100 in the liver (1). The production of B48 is the result of a tissue specific mRNA processing occurring in the small intestine (2,3). The translation of B48 and B100 in the endoplasmic reticulum (ER) is directly coupled with the assembly of two major classes of lipoproteins: chylomicrons and very low density lipoproteins (VLDL) (4).Although an apoB structure at atomic resolution is still unavailable, it is generally accepted that the full length apoB has an βα1-β1-α2-β2-α3 pentapartite domain organization, in which α represents predominantly α-helical structures and β corresponds to β-sheets (5). According to this model, apoB is depicted as a belt wrapped around a lipoprotein particle (6). Evidence from electron microscopy indicates that the N-terminus of apoB, largely the βα1 domain, is globularly folded and protrudes away from the LDL particle (7,8). These findings are consistent

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“…The Vg domain has lipid affinity, and it appears to be important for the assembly of the lipoprotein complex (15,16). The apoB Vg domain binds to egg phosphatidylcholine (PC) monolayers and dimyristoylphos-phatidylcholine multilamellar vesicles that have been used in the studies of the apoB-lipid packing (15,17), which takes place at the endoplasmic reticulum membrane.…”

mentioning

confidence: 99%

Vitellogenin Recognizes Cell Damage through Membrane Binding and Shields Living Cells from Reactive Oxygen Species

Havukainen

Münch

Baumann

et al. 2013

Journal of Biological Chemistry

106

120

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Background: Vitellogenin is a central regulator of honey bee life span by largely unknown mechanisms. Results: Honey bee vitellogenin has membrane affinity that is connected to cell damage recognition and antioxidant function. Conclusion: Membrane binding documents a new molecular behavior among vitellogenins. Significance: Vitellogenins are widespread phylogenetically, and their molecular behavior is essential for fitness traits in many animals.

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Assembly of Lipoprotein Particles Containing Apolipoprotein-B: Structural Model for the Nascent Lipoprotein Particle

Cited by 70 publications

References 47 publications

Microsomal Triglyceride Transfer Protein Activity Is Not Required for the Initiation of Apolipoprotein B-containing Lipoprotein Assembly in McA-RH7777 Cells

Microsomal Triglyceride Transfer Protein Activity Is Not Required for the Initiation of Apolipoprotein B-containing Lipoprotein Assembly in McA-RH7777 Cells

Defining Lipid-Interacting Domains in the N-Terminal Region of Apolipoprotein B

Vitellogenin Recognizes Cell Damage through Membrane Binding and Shields Living Cells from Reactive Oxygen Species

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