Structurally disparate molecules reportedly engage and activate Toll-like receptor (TLR) 4 and other TLRs, yet the interactions that mediate binding and activation by dissimilar ligands remain unknown. We describe Neoseptins, chemically synthesized peptidomimetics that bear no structural similarity to the established TLR4 ligand, lipopolysaccharide (LPS), but productively engage the mouse TLR4 (mTLR4)/ myeloid differentiation factor 2 (MD-2) complex. Neoseptin-3 activates mTLR4/MD-2 independently of CD14 and triggers canonical myeloid differentiation primary response gene 88 (MyD88)- and Toll-interleukin 1 receptor (TIR) domain-containing adaptor inducing IFN-beta (TRIF)- dependent signaling. The crystal structure mTLR4/MD-2/Neoseptin-3 at 2.57-Å resolution reveals that Neoseptin-3 binds as an asymmetrical dimer within the hydrophobic pocket of MD-2, inducing an active receptor complex similar to that induced by lipid A. However, Neoseptin-3 and lipid A form dissimilar molecular contacts to achieve receptor activation; hence strong TLR4/MD-2 agonists need not mimic LPS.
|Original language||American English|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - 16 Feb 2016|
Bibliographical noteFunding Information:
We thank Ian Wilson for the initial design of the mouse TLR4VLR and MD2-protein A hybrid constructs for coexpression of the complex; Jose Rizo-Rey for help with the NMR experiments; Diana Tomchick and Srinivasan Raghunathan for help with X-ray data collection and structure determination; and Peter Jurek and Anne Murray for assistance with manuscript preparation. Results shown in this report are derived from work performed at Argonne National Laboratory, Structural Biology Center at Advanced Photon Source. Argonne is operated by UChicago Argonne, LLC, for the US Department of Energy, Office of Biological and Environmental Research under Contract DE-AC02-06CH11357. This work was supported by NIH/National Institute of General Medical Sciences (NIGMS) Grant R01GM104496 (to H.Z.) and NIH/National Institute of Allergy and Infectious Diseases (NIAID) Grants U24 AI082657 (to B.B. and D.L.B.) and U19 AI100627 (to B.B.).
- Crystal structure
- Innate immunity
- Peptidomimetic compounds
- Proinflammatory response