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A short amphipathic alpha helix in scavenger receptor BI facilitates bidirectional HDL-cholesterol transport. J Biol Chem 2022 Sep;298(9):102333

Date

08/05/2022

Pubmed ID

35926711

Pubmed Central ID

PMC9436806

DOI

10.1016/j.jbc.2022.102333

Scopus ID

2-s2.0-85136562503 (requires institutional sign-in at Scopus site)   3 Citations

Abstract

During reverse cholesterol transport, high-density lipoprotein (HDL) carries excess cholesterol from peripheral cells to the liver for excretion in bile. The first and last steps of this pathway involve the HDL receptor, scavenger receptor BI (SR-BI). While the mechanism of SR-BI-mediated cholesterol transport has not yet been established, it has long been suspected that cholesterol traverses through a hydrophobic tunnel in SR-BI's extracellular domain. Confirmation of a hydrophobic tunnel is hindered by the lack of a full-length SR-BI structure. Part of SR-BI's structure has been resolved, encompassing residues 405 to 475, which includes the C-terminal transmembrane domain and its adjacent extracellular region. Within the extracellular segment is an amphipathic helix (residues 427-436, referred to as AH(427-436)) that showed increased protection from solvent in NMR-based studies. Homology models predict that hydrophobic residues in AH(427-436) line a core cavity in SR-BI's extracellular region that may facilitate cholesterol transport. Therefore, we hypothesized that hydrophobic residues in AH(427-436) are required for HDL cholesterol transport. Here, we tested this hypothesis by mutating individual residues along AH(427-436) to a charged residue (aspartic acid), transiently transfecting COS-7 cells with plasmids encoding wild-type and mutant SR-BI, and performing functional analyses. We found that mutating hydrophobic, but not hydrophilic, residues in AH(427-436) impaired SR-BI bidirectional cholesterol transport. Mutating phenylalanine-430 was particularly detrimental to SR-BI's functions, suggesting that this residue may facilitate important interactions for cholesterol delivery within the hydrophobic tunnel. Our results support the hypothesis that a hydrophobic tunnel within SR-BI mediates cholesterol transport.

Author List

May SC, Sahoo D

Author

Daisy Sahoo PhD Vice Chair, Professor in the Medicine department at Medical College of Wisconsin




MESH terms used to index this publication - Major topics in bold

Aspartic Acid
Biological Transport
CD36 Antigens
Cholesterol, HDL
Lipoproteins, HDL
Phenylalanine
Protein Conformation, alpha-Helical
Receptors, Lipoprotein
Scavenger Receptors, Class B
Solvents