scholarly journals Proline residues in scavenger receptor-BI's C-terminal region support efficient cholesterol transport

2019 ◽  
Vol 476 (6) ◽  
pp. 951-963
Author(s):  
Sarah C. Proudfoot ◽  
Daisy Sahoo
Keyword(s):  
Reverse Cholesterol Transport ◽  
Transmembrane Domain ◽  
Scavenger Receptor ◽  
Resonance Structure ◽  
High Density Lipoproteins ◽  
Cholesterol Transport ◽  
Nuclear Magnetic Resonance Structure ◽  
Scavenger Receptor Bi ◽  
High Affinity Receptor ◽  
Mutant Receptors

Abstract High-density lipoproteins (HDLs) facilitate reverse cholesterol transport, a process in which HDL removes cholesterol from circulation and carries it to the liver for biliary excretion. Reverse cholesterol transport is also facilitated by HDL's high-affinity receptor, scavenger receptor-BI (SR-BI), by mechanisms that are not fully understood. To improve our understanding of SR-BI function, we previously solved the NMR (nuclear magnetic resonance) structure of a peptide encompassing amino acids 405–475 of SR-BI. This segment of SR-BI, that includes the functionally critical C-terminal transmembrane domain and part of the extracellular domain, also contains four conserved proline (Pro) residues. We hypothesized that these proline residues support SR-BI in a conformation that allows for efficient cholesterol transport. To test this, we generated individual Pro-to-alanine mutations in full-length SR-BI and transiently expressed the mutant receptors in COS-7 cells to measure the effects on SR-BI-mediated cholesterol transport functions. Our findings reveal that HDL cell association and uptake of HDL-cholesteryl esters are impaired by mutation of Pro-412, Pro-438, or the transmembrane proline kink residue (Pro-459). In addition, SR-BI-mediated cholesterol efflux and membrane cholesterol distribution are impaired by mutation of Pro-412 or Pro-438, indicating that these residues are essential for a fully functional SR-BI receptor. Furthermore, we demonstrate that Pro-408 is necessary for proper SR-BI expression, but mutation of Pro-408 does not cause SR-BI to become misfolded or rapidly degraded by the proteasome or the lysosome. We conclude that key proline residues play an important role in SR-BI function by allowing for the efficient transport of cholesterol between cells and HDL.

scholarly journals HDL mediates reverse cholesterol transport from ram spermatozoa and induces hyperactivated motility

2021 ◽  
Author(s):  
Naomi C Bernecic ◽  
Simon P Graaf ◽  
Tamara Leahy ◽  
Bart M Gadella
Keyword(s):  
Reverse Cholesterol Transport ◽  
Cholesterol Efflux ◽  
Scavenger Receptor ◽  
High Density Lipoproteins ◽  
In Vitro Fertilisation ◽  
Critical Event ◽  
Cholesterol Transport ◽  
Type I

ABSTRACT Reverse Cholesterol Transport or cholesterol efflux is part of an extensive plasma membrane remodelling process in spermatozoa that is imperative for fertilisation. For ram spermatozoa, sheep serum is well known to support in vitro fertilisation (IVF), but knowledge of its explicit role is limited. Though, it is postulated to elicit cholesterol efflux owing to the presence of high density lipoproteins (HDLs) that interact with transmembrane cholesterol transporters, such as ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B, type I (SR-BI). In this study, we report that both sheep serum and HDLs were able to elicit cholesterol efflux alone by up to 20–40% (as measured by the BODIPY-cholesterol assay). Furthermore, when the antagonists glibenclamide and valspodar were used to inhibit the function of ABCA1 and SR-BI or ABCA1 alone, respectively, cholesterol efflux was only marginally reduced (8–15)%. Nevertheless, it is likely that in ram spermatozoa, a specific facilitated pathway of cholesterol efflux is involved in the interaction between cholesterol acceptors and transporters. Interestingly, exposure to HDLs also induced hyperactivated motility, another critical event required for successful fertilisation. Taken together, this study details the first report of the dual action of HDLs on ram spermatozoa, providing both an insight into the intricacy of events leading up to fertilisation in vivo as well as demonstrating the possible application of HDL supplementation in media for IVF.

scholarly journals Scavenger receptor BI and ABCG5/G8 differentially impact biliary sterol secretion and reverse cholesterol transport in mice

Hepatology ◽  
2013 ◽  
Vol 58 (1) ◽  
pp. 293-303 ◽  
Author(s):  
Arne Dikkers ◽  
Jan Freak de Boer ◽  
Wijtske Annema ◽  
Albert K. Groen ◽  
Uwe J.F. Tietge
Keyword(s):  
Reverse Cholesterol Transport ◽  
Scavenger Receptor ◽  
Cholesterol Transport ◽  
Scavenger Receptor Bi

Abstract 522: Scavenger Receptor-BI’s Cholesterol Transport Functions are Dependent on its Extracellular Tryptophan Residues

2015 ◽  
Vol 35 (suppl_1) ◽  
Author(s):  
Rebecca L Holme ◽  
James J Miller ◽  
Daisy Sahoo
Keyword(s):  
Cholesterol Oxidase ◽  
Scavenger Receptor ◽  
Density Lipoprotein ◽  
Surface Expression ◽  
Structural Features ◽  
Cell Surface Expression ◽  
Cholesterol Transport ◽  
Scavenger Receptor Bi ◽  
Atherogenic Particle ◽  
Mutant Receptors

High density lipoprotein (HDL) functions as an anti-atherogenic particle, primarily due to its role in reverse cholesterol transport whereby HDL delivers cholesterol to the liver for excretion upon interaction with its receptor, scavenger receptor BI (SR-BI). The extracellular domain of SR-BI is required for its cholesterol transport functions, yet our understanding of the molecular and structural features of this domain remains limited. We designed experiments to test the hypothesis that one or more of the six highly conserved extracellular tryptophan (Trp; W) residues are critical for mediating receptor function. Towards this end, we created a series of Trp-to-Phe mutant receptors of SR-BI, as well as Trp-free SR-BI and assessed the ability of these mutant receptors to mediate cholesterol transport. Wild-type (WT) or mutant SR-BI receptors were transiently expressed in COS7 cells and proper cell surface expression was confirmed by immunoblotting, confocal microscopy and flow cytometry. Next, we showed that Trp-free- and W415F-SR-BI had a significantly decreased ability to bind HDL (12.7% and 31.3% of WT levels, respectively) and promote selective uptake of HDL-cholesteryl esters (35.2% and 70.1% of WT levels, respectively). Interestingly, only Trp-free-, but not W415F-SR-BI, showed an impaired ability to mediate efflux of free cholesterol (FC) (90.8% decrease vs. WT). Furthermore, both W415F- and Trp-free SR-BI were unable to reorganize plasma membrane pools of FC based on lack of sensitivity of FC to exogenous cholesterol oxidase. We then designed an additional set of mutant SR-BI receptors to determine whether restoration of Trp415 alone (or in combination with other Trp residues) could rescue SR-BI function. Restoration of Trp415 into Trp-free-SR-BI partially rescued cholesterol transport functions. Addition of any of the other 5 extracellular Trp residues was also not sufficient to restore WT cholesterol transport function in combination with Trp415. In summary, loss of all Trp residues in SR-BI impairs its cholesterol transport functions, mostly due to the loss of Trp415. Homology modeling of SR-BI based on the crystal structure of LIMP-2, a member of the same protein family, may help identify the importance of this residue in future studies.

scholarly journals Apolipoprotein A1-Related Proteins and Reverse Cholesterol Transport in Antiatherosclerosis Therapy: Recent Progress and Future Perspectives

2022 ◽  
Vol 2022 ◽  
pp. 1-9
Author(s):  
Xiuting Xu ◽  
Zikai Song ◽  
Bao Mao ◽  
Guoliang Xu
Keyword(s):  
Reverse Cholesterol Transport ◽  
Scavenger Receptor ◽  
Cholesterol Acyltransferase ◽  
Density Lipoprotein ◽  
Coronary Artery Occlusion ◽  
Artery Occlusion ◽  
The Body ◽  
Apolipoprotein A1 ◽  
Cholesterol Transport ◽  
Class B

Hyperlipidemia characterized by abnormal deposition of cholesterol in arteries can cause atherosclerosis and coronary artery occlusion, leading to atherosclerotic coronary heart disease. The body prevents atherosclerosis by reverse cholesterol transport to mobilize and excrete cholesterol and other lipids. Apolipoprotein A1, the major component of high-density lipoprotein, plays a key role in reverse cholesterol transport. Here, we reviewed the role of apolipoprotein A1-targeting molecules in antiatherosclerosis therapy, in particular ATP-binding cassette transporter A1, lecithin-cholesterol acyltransferase, and scavenger receptor class B type 1.

Abstract 631: Lipid Composition of Gold Nanoparticle-Templated High-Density Lipoprotein Analogs Dictates Cholesterol Efflux Function

2014 ◽  
Vol 34 (suppl_1) ◽  
Author(s):  
R Kannan Mutharasan ◽  
Amritha T Singh ◽  
Kaylin M McMahon ◽  
C Shad Thaxton
Keyword(s):  
Fatty Acid ◽  
Lipid Content ◽  
Lipid Composition ◽  
Reverse Cholesterol Transport ◽  
Cholesterol Efflux ◽  
Lipid Membrane ◽  
Density Lipoprotein ◽  
High Density ◽  
High Density Lipoproteins ◽  
Cholesterol Transport

Background: Reverse cholesterol transport, the process by which cholesterol is effluxed from cells to high-density lipoproteins (HDL) and is delivered to the liver for clearance, is a promising pathway to augment for treatment of atherosclerosis. Though structure-function relationships for nascent, discoidal HDL and cholesterol efflux have been well studied, how the lipid composition of spherical HDL species - which varies in pathophysiological conditions - impacts their ability to mediate cholesterol efflux has not been investigated. Methods and Results: Spherical gold nanoparticles (5 nm) were used to synthesize spherical HDL analogs (HDL-NP) by adding ApoAI protein, and various lipids. With this strategy a panel of HDL-NP varying in lipid content was generated. HDL-NP designs tested include: dipalmitylphosphatidylcholine (DPPC, saturated fatty acid), dioleoylphosphatidylcholine (DOPC, unsaturated fatty acid), sphingomyelin, lysophosphatidylcholine (LPC), and mixtures thereof. All of these species are found in natural HDL. After characterizing protein and lipid stoichiometry of the purified HDL-NP, these HDL-NP designs were tested in the cellular reverse cholesterol transport assay using J774 mouse macrophages. These studies demonstrate that all HDL-NP designs mediate more efflux than equimolar amounts of ApoAI protein control, and further demonstrate that HDL-NP designs incorporating unsaturated phospholipid (DOPC), sphingomyelin, and LPC - each of which can increase disorder in the lipid membrane and thus give rise to opportunity for cholesterol to intercalate and bind - enhance cholesterol efflux compared to saturated phospholipid (DPPC) design. Conclusion: In summary, these results demonstrate that lipid content of HDL-NP - analogs of spherical HDL - dictates cholesterol efflux function, a finding which sheds light on the functional importance of lipid content variation seen in mature, spherical HDL species.

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