Plasma cholesteryl ester transfer protein has binding sites for neutral lipids and phospholipids.

Swenson, T L; Brocia, R W; Tall, Alan R.

doi:10.1016/s0021-9258(18)60692-1

Cited by 79 publications

(19 citation statements)

References 21 publications

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“…However, it is important to note that this model does not adequately explain CETP-mediated lipid transfers that occur when HDL is absent, and Lauer et al (34) demonstrated that ternary complex formation is not a prerequisite for lipid transfer. In the other prevailing transfer mechanism, CETP functions as a lipid shuttle between any two lipoproteins (35,36). Because E9-deleted CETP retains the C-terminal 26 amino acids essential for its lipid transfer activity (23,37,38), it is plausible that E9-deleted CETP retains the ability to promote lipid transfer by this carrier mechanism.…”

Section: Discussionmentioning

confidence: 99%

Exon 9-deleted CETP inhibits full length-CETP synthesis and promotes cellular triglyceride storage

Izem

Liu

Morton

2020

Journal of Lipid Research

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Cholesteryl ester transfer protein (CETP) exists as full-length (FL) and exon 9 (E9)-deleted isoforms. The function of E9-deleted CETP is poorly understood. Here, we investigated the role of E9-deleted CETP in regulating the secretion of FL-CETP by cells and explored its possible role in intracellular lipid metabolism. CETP overexpression in cells that naturally express CETP confirmed that E9-deleted CETP is not secreted, and showed that cellular FL- and E9-deleted CETP form an isolatable complex. Coexpression of CETP isoforms lowered cellular levels of both proteins and impaired FL-CETP secretion. These effects were due to reduced synthesis of both isoforms; however, the predominate consequence of FL- and E9-deleted CETP coexpression is impaired FL-CETP synthesis. We reported previously that reducing both CETP isoforms or overexpressing FL-CETP impairs cellular triglyceride (TG) storage. To investigate this further, E9-deleted CETP was expressed in SW872 cells that naturally synthesize CETP and in mouse 3T3-L1 cells that do not. E9-deleted CETP overexpression stimulated SW872 triglyceride synthesis and increased stored TG 2-fold. Expression of E9-deleted CETP in mouse 3T3-L1 cells produced a similar lipid phenotype. In vitro, FL-CETP promotes the transfer of TG from ER-enriched membranes to lipid droplets. E9-deleted CETP also promoted this transfer, although less effectively, and it inhibited the transfer driven by FL-CETP. We conclude that FL- and E9-deleted CETP isoforms interact to mutually decrease their intracellular levels and impair FL-CETP secretion by reducing CETP biosynthesis. E9-deleted CETP, like FL-CETP, alters cellular TG metabolism and storage but in a contrary manner.

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Section: Discussionmentioning

confidence: 99%

Exon 9-deleted CETP inhibits full length-CETP synthesis and promotes cellular triglyceride storage

Izem

Liu

Morton

2020

Journal of Lipid Research

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“…CETP is a hydrophobic glycoprotein of 476 amino acids with a molecular mass of about 68,000-70,000 daltons in SDS gels (8)(9)(10). CETP has binding sites for CE, triglyceride (TG), and phospholipids (11) and is thought to transfer lipids through carrier mediated and/or collisional mechanisms (12,13). Both the binding of CETP to its lipoprotein substrates and the ability of CETP to bind neutral lipid have been suggested to be essential events in the neutral lipid transfer mechanism (11,14).…”

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confidence: 99%

“…CETP has binding sites for CE, triglyceride (TG), and phospholipids (11) and is thought to transfer lipids through carrier mediated and/or collisional mechanisms (12,13). Both the binding of CETP to its lipoprotein substrates and the ability of CETP to bind neutral lipid have been suggested to be essential events in the neutral lipid transfer mechanism (11,14). The COOH terminus of the protein is important for the neutral lipid transfer activity as demonstrated by experiments using monoclonal antibodies (mAb) that bind at the COOH terminus and neutralize neutral lipid transfer activity (15) and by deletional and point mutagenesis of the COOH-terminal region (16)(17)(18).…”

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confidence: 99%

“…Binding of Cholesteryl Ester to CETP-The binding of CE to CETP was assessed by the procedure of Swenson et al (11). Egg PC vesicles (12 nmol) containing 1.5 mol % cholesteryl oleate and 0.09 /LCi of [3HJcholesteryl oleate (egg PC/[3H]CE) were incubated with CETP in 10 mM Tris-Cl, 1 mM EDTA (TE buffer), and 2 mg of BSA at 37°C for 1 h in a total volume of 1 m!.…”

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confidence: 99%

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Defective Binding of Neutral Lipids by a Carboxyl-terminal Deletion Mutant of Cholesteryl Ester Transfer Protein

Wang

Kussie

Deng

et al. 1995

Journal of Biological Chemistry

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The plasma cholesteryl ester transfer protein (CETP, 476 amino acids) transfers cholesteryl ester (CE) from high density lipoprotein (HDL) to triglyceride-rich lipoproteins and plays a major role in HDL catabolism. Using deletional and site-directed mutagenesis, we previously showed that the carboxyl terminus of human CETP comprises the epitope of a neutralizing monoclonal antibody and is necessary for neutral lipid transfer activity. To assess the nature of the involvement of the COOH terminus in cholesteryl ester transfer activity, we characterized a deletion mutant of CETP lacking amino acid residues 470-475 in terms of CE transfer kinetics, association with HDL, and capacity to bind CE, triglyceride (TG), and phosphatidylcholine (PC). Kinetic analysis indicated a major catalytic defect of the deletion mutant, as shown by markedly decreased maximum cholesteryl ester transfer activities (apparent Vmax) for donor (HDL) and acceptor (low density lipoprotein (LDL)) lipoproteins but there were no significant changes of concentrations of the donor and acceptor at 50% Vmax (apparent Km). The binding of CETP to HDL, as determined by native gel electrophoresis, was similar for wild-type and mutant protein. When egg PC/CE vesicles were incubated with wild type CETP and then separated by gel filtration chromatography, there was maximum binding of about 1 mol of CE/mol of CETP. Under similar conditions the mutant CETP bound 0.09-0.37 mol of CE/mol of protein. Similarly, when egg PC/TG vesicles were incubated with the CETP proteins, there was a maximum binding of 0.5 mol of triglyceride/mol of wild-type CETP, whereas there was only 0.00-0.07 mol of TG/mol of deletion mutant. The binding of phosphatidylcholine was similar for wild-type and the deletion mutant. The studies suggest that amino acids 470-475 (forming part of a COOH-terminal amphipathic helix) are involved in CE and TG binding by CETP but are not required either for the binding of PC by CETP or the association of CETP with HDL. The COOH terminus of CETP may comprise a neutral lipid binding site directly involved in the lipid transfer mechanism.

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“…The exact mechanism of PLTP-mediated phospholipid transfer is currently under debate. A carrier-type transfer mechanism has been suggested both for PLTP (15) and the related CETP (36,37). On the other hand, the wide substrate specificity spectrum of PLTP (11,12) and the apparent absence of a stable PLTP-phospholipid intermediate (11) argue against a traditional carrier mechanism.…”

Section: Discussionmentioning

confidence: 99%

Structure and phospholipid transfer activity of human PLTP: analysis by molecular modeling and site-directed mutagenesis

Huuskonen

Wohlfahrt

Jauhiainen

et al. 1999

Journal of Lipid Research

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The plasma phospholipid transfer protein (PLTP) is an important regulator of high density lipoprotein (HDL) metabolism. We have here, based on sequence alignments of the plasma LPS-binding/lipid transfer protein family and the X-ray structure of the bactericidal/permeability increasing protein (BPI), modeled the structure of PLTP. The model predicts a two-domain architecture with conserved lipid-binding pockets consisting of apolar residues in each domain. By site-directed mutagenesis of selected amino acid residues and transient expression of the protein variants in HeLa cells, the pockets are shown to be essential for PLTP-mediated phospholipid transfer. A solid phase ligand binding assay was used to determine the HDL-binding ability of the mutants. The results suggest that the observed decreases in phospholipid transfer activity of the N-terminal pocket mutants cannot be attributed to altered HDLbinding, but the C-terminal lipid-binding pocket may be involved in the association of PLTP with HDL. Further, the essential structural role of a disulfide bridge between cysteine residues 146 and 185 is demonstrated. The structural model and the mutants characterized here provide powerful tools for the detailed analysis of the mechanisms of PLTP function. -Huuskonen, J., G. Wohlfahrt, M. Jauhiainen, C. Ehnholm, O. Teleman, and V. M. Olkkonen. Structure and phospholipid transfer activity of human PLTP: analysis by molecular modeling and site-directed mutagenesis.

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Plasma cholesteryl ester transfer protein has binding sites for neutral lipids and phospholipids.

Cited by 79 publications

References 21 publications

Exon 9-deleted CETP inhibits full length-CETP synthesis and promotes cellular triglyceride storage

Exon 9-deleted CETP inhibits full length-CETP synthesis and promotes cellular triglyceride storage

Defective Binding of Neutral Lipids by a Carboxyl-terminal Deletion Mutant of Cholesteryl Ester Transfer Protein

Structure and phospholipid transfer activity of human PLTP: analysis by molecular modeling and site-directed mutagenesis

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