Exoplasmic cysteine Cys384 of the HDL receptor SR-BI is critical for its sensitivity to a small-molecule inhibitor and normal lipid transport activity
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Krieger-2011-July-Cys384 of the HDL receptor.pdf
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Author(s)
Saenz-Vash, Veronica
Romer, Katherine A.
Xu, Shangzhe
Yesilaltay, Ayce
Krieger, Monty
Yu, Miao
Nieland, Thomas J
Penman, Marsha L
Carr, Steven A
Date Issued
July 2011
Journal
Proceedings of the National Academy of Sciences
Publisher
Proceedings of the National Academy of Sciences (PNAS)
Citation
Yu, M. et al. “Exoplasmic cysteine Cys384 of the HDL receptor SR-BI is critical for its sensitivity to a small-molecule inhibitor and normal lipid transport activity.” Proceedings of the National Academy of Sciences 108.30 (2011): 12243-12248. Web. 1 Feb. 2012.
Version
Final published version
Abstract
The HDL receptor, scavenger receptor, class B, type I (SR-BI), is a homooligomeric cell surface glycoprotein that controls HDL structure and metabolism by mediating the cellular selective uptake of lipids, mainly cholesteryl esters, from HDL. The mechanism underlying SR-BI-mediated lipid transfer, which differs from classic receptor-mediated endocytosis, involves a two-step process (binding followed by lipid transport) that is poorly understood. Our previous structure/activity analysis of the small-molecule inhibitor blocker of lipid transport 1 (BLT-1), which potently (IC[subscript 50] ∼ 50 nM) blocks SR-BI-mediated lipid transport, established that the sulfur in BLT-1’s thiosemicarbazone moiety was essential for activity. Here we show that BLT-1 is an irreversible inhibitor of SR-BI, raising the possibility that cysteine(s) in SR-BI interact with BLT-1. Mass spectrometric analysis of purified SR-BI showed two of its six exoplasmic cysteines have free thiol groups (Cys251 and Cys384). Converting Cys384 (but not Cys251) to serine resulted in complete BLT-1 insensitivity, establishing that the unique molecular target of BLT-1 inhibition of cellular SR-BI dependent lipid transport is SR-BI itself. The C384S substitution reduced the receptor’s intrinsic lipid uptake activity by approximately 60% without dramatically altering its surface expression, homooligomerization, or HDL binding. Thus, a small-molecule screening approach identified a key residue in SR-BI involved in lipid transport, providing a powerful springboard into the analyses of the structure and mechanism of SR-BI, and highlighting the power of this approach for such analyses.
MIT Department
Massachusetts Institute of Technology. Computational and Systems Biology Program
Massachusetts Institute of Technology. Department of Biology
Koch Institute for Integrative Cancer Research at MIT
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DOI of Published Version
https://doi.org/10.1073/pnas.1109078108
