Sulfatides are endogenous ligands for the TLR4–MD-2 complex

Lijing Su*, Muhammad Athamna, Ying Wang, Junmei Wang, Marina Freudenberg, Tao Yue, Jianhui Wang, Eva Marie Y. Moresco, Haoming He, Tsaffrir Zor*, Bruce Beutler*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

Many endogenous molecules, mostly proteins, purportedly activate the Toll-like receptor 4 (TLR4)–myeloid differentiation factor-2 (MD-2) complex, the innate immune receptor for lipopolysaccharide (LPS) derived from gram-negative bacteria. However, there is no structural evidence supporting direct TLR4–MD-2 activation by endogenous ligands. Sulfatides (3-O-sulfogalactosylceramides) are natural, abundant sulfated glycolipids that have variously been shown to initiate or suppress inflammatory responses. We show here that short fatty acid (FA) chain sulfatides directly activate mouse TLR4–MD-2 independent of CD14, trigger MyD88- and TRIF-dependent signaling, and stimulate tumor necrosis factor α (TNFα) and type I interferon (IFN) production in mouse macrophages. In contrast to the agonist activity toward the mouse receptor, the tested sulfatides antagonize TLR4–MD-2 activation by LPS in human macrophage-like cells. The agonistic and antagonistic activities of sulfatides require the presence of the sulfate group and are inversely related to the FA chain length. The crystal structure of mouse TLR4–MD-2 in complex with C16-sulfatide revealed that three C16-sulfatide molecules bound to the MD-2 hydrophobic pocket and induced an active dimer conformation of the receptor complex similar to that induced by LPS or lipid A. The three C16-sulfatide molecules partially mimicked the detailed interactions of lipid A to achieve receptor activation. Our results suggest that sulfatides may mediate sterile inflammation or suppress LPS-stimulated inflammation, and that additional endogenous negatively charged lipids with up to six lipid chains of limited length might also bind to TLR4–MD-2 and activate or inhibit this complex.

Original languageEnglish
Article numbere2105316118
JournalProceedings of the National Academy of Sciences of the United States of America
Volume118
Issue number30
DOIs
StatePublished - 27 Jul 2021

Funding

FundersFunder number
Ministry of Science of Israel
National Institutes of HealthAI100627
National Institutes of Health
National Institute of Allergy and Infectious DiseasesR01AI125581
National Institute of Allergy and Infectious Diseases
Office of the DirectorS10OD025018
Office of the Director
Lyda Hill Foundation
Israel Cancer Association20180115
Israel Cancer Association
Israel Science Foundation2142/20
Israel Science Foundation

    Keywords

    • Autoimmunity
    • Endogenous ligand
    • Innate immunity
    • Toll-like receptor
    • X-ray crystallography

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