Structural biology provides long-sought solution to innate immunity
puzzle
Date:
July 22, 2021
Source:
UT Southwestern Medical Center
Summary:
Researchers report the first structural confirmation that endogenous
- - or self-made -- molecules can set off innate immunity in mammals
via a pair of immune cell proteins called the TLR4-MD-2 receptor
complex. The work has wide-ranging implications for finding ways
to treat and possibly prevent autoimmune diseases such as multiple
sclerosis and antiphospholipid syndrome.
FULL STORY ==========================================================================
UT Southwestern researchers report the first structural confirmation that endogenous -- or self-made -- molecules can set off innate immunity in
mammals via a pair of immune cell proteins called the TLR4-MD-2 receptor complex. The work has wide-ranging implications for finding ways to treat
and possibly prevent autoimmune diseases such as multiple sclerosis and antiphospholipid syndrome.
==========================================================================
The TLR4-MD-2 receptor complex is well known for its role in the body's response to infection by gram-negative bacteria. Its role in autoimmunity
had been long suspected, although direct proof was lacking. The team,
led by Nobel Laureate Bruce Beutler, M.D., director of the Center for
the Genetics of Host Defense (CGHD), identified lipids called sulfatides
that can activate the innate immunity sensor TLR4, located on a cell's membrane. His discovery of the genes behind the TLR4 receptor and its
role in the body's earliest response to infection -- innate immunity --
led to his 2011 Nobel Prize in Physiology or Medicine.
Beutler is corresponding author of the study published this week
in the Proceedings of the National Academy of Sciences that used
X-ray crystallography to confirm how sulfatides bind to the receptor
complex. Lead author Lijing Su, Ph.D., a CGHD assistant professor with a secondary appointment in biophysics, conducted the X-ray crystallography
at UT Southwestern's Structural Biology Core Facility and at Argonne
National Laboratory in Illinois.
"For many years, the question of whether endogenous -- or self --
molecules can activate innate immune receptors has been an important one,"
says Beutler, a professor of immunology and internal medicine. "Scientists
had observed that our own nucleic acids can activate TLRs 3, 7, 8, and 9, causing inflammation and autoimmunity. Many endogenous ligands for TLR4,
most of them proteins, have been proposed. This is the first study to substantiate the existence of such a TLR4 ligand, meaning a molecule that
fits into the receptor, by structural studies." The team's structural
studies of mouse TLR4-MD-2 in complex with sulfatides gave a detailed
look at how sulfatides bind to the U-shaped side of the receptor complex
in order to activate it. That binding sets off biological pathways that
lead to the body's inflammatory response.
The study, which raises new and important questions, includes some
observations about differences in the way the receptor responds in mice
and humans. It also raises new questions about how the chemical makeup
of individual sulfatides might affect the way they interact with the
receptor complex to activate or suppress the immune response.
"Our work demonstrates that these, or perhaps other endogenous lipids,
may indeed trigger activation of TLR4," Beutler says, adding that TLR4
usually acts as a sensor of lipopolysaccharide (a lipid plus sugar
molecule) -- also known as endotoxin -- that resides on gram-negative
bacteria. TLR4-LPS binding is implicated in sepsis, a potentially deadly condition in which the immune system goes into overdrive in response
to infection.
Su adds that she and others in the Beutler lab previously reported that
TLR4 and its co-receptor MD-2 can be activated by a synthetic small
molecule called neoseptin-3, created in collaboration with the laboratory
of Dale Boger, Ph.D., at The Scripps Research Institute, which shares
no structural similarity to the natural microbial ligand, LPS.
"Our crystal structure of mouse TLR4-MD-2 in complex with neoseptin-3
revealed that this receptor complex might accommodate multiple small
molecules rather than a big molecule like LPS," Su explains. "This result
led us to look for natural lipids that might bind and activate TLR4-MD-2 signaling. Among early candidates were phosphoceramides, but these failed
to activate the receptor.
Structural features of sulfatides, and their great abundance in
some tissues, led us to test them instead, and we confirmed that some sulfatides do indeed activate TLR4." UTSW co-authors include Ying Wang,
Tao Yue, Jianhui Wang, and Eva Marie Y.
Moresco. Researchers from Israel, Pittsburgh, Pennsylvania, and Germany
also participated in the work.
The investigation received support from the National Institutes of Health (grants AI125581 and AI100627), the Lyda Hill Foundation, the Israel
Cancer Association (grant 20180115), the Israel Science Foundation
(grant 2142/20), and the Ministry of Science of Israel. The work at
Argonne received support from the U.S. Department of Energy (contract DE-AC02-06CH11357). The research also received support from the Office
of the Director, NIH (award S10OD025018).
Beutler, a Regental Professor, holds the Raymond and Ellen Willie
Distinguished Chair in Cancer Research, in Honor of Laverne and Raymond
Willie, Sr.
========================================================================== Story Source: Materials provided by UT_Southwestern_Medical_Center. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Lijing Su, Muhammad Athamna, Ying Wang, Junmei Wang, Marina
Freudenberg,
Tao Yue, Jianhui Wang, Eva Marie Y. Moresco, Haoming He, Tsaffrir
Zor, Bruce Beutler. Sulfatides are endogenous ligands for the
TLR4-MD- 2 complex. Proceedings of the National Academy of Sciences,
2021; 118 (30): e2105316118 DOI: 10.1073/pnas.2105316118 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/07/210722112920.htm
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