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Paclitaxel binding to human and murine MD-2
Shanta M Zimmer1, Jin Liu2, Jaime L Clayton2
1Department of Chemistry, Emory University, Atlanta, Georgia 30322.
The Journal of Biological Chemistry
|July 25, 2008
Summary
Paclitaxel (PTX) activates the Toll-like receptor 4 (TLR4) innate immune pathway through binding to MD-2, but this interaction is species-specific. Murine MD-2 is required for PTX-induced TLR4 activation in humans, unlike in mice.
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Paclitaxel (PTX) is a chemotherapy drug that targets beta-tubulin and induces apoptosis via the Toll-like receptor 4 (TLR4) pathway.
- MD-2 is a crucial accessory protein for TLR4 activation, and its interaction with PTX is known to be species-specific in murine cells.
- The precise binding of PTX to human MD-2 and the subsequent TLR4 interaction remain incompletely understood.
Purpose of the Study:
- To investigate whether Paclitaxel (PTX) binds to human MD-2.
- To elucidate the interaction mechanisms between MD-2, TLR4, and PTX.
- To identify the structural basis for the species-specific activation of TLR4 by PTX.
Main Methods:
- Produced recombinant human MD-2 (rhMD-2) using a Pichia pastoris expression system.
- Assessed PTX-rhMD-2 binding using enzyme-linked immunosorbent assay (ELISA).
- Evaluated TLR4 activation by measuring human tumor necrosis factor alpha production in THP-1 monocytes and HEK293 cells transfected with various combinations of human and murine TLR4 and MD-2.
- Performed computational docking of PTX onto crystal structures of murine and human MD-2.
Main Results:
- Paclitaxel (PTX) directly binds to recombinant human MD-2 (rhMD-2) in a dose-dependent manner, inhibited by anti-MD-2 antibodies.
- Human monocytes and HEK293 cells expressing human MD-2 showed poor responsiveness to PTX, while murine cells responded robustly.
- HEK293 cells transfected with murine MD-2 and human TLR4 were highly responsive to PTX, indicating murine MD-2 is essential for PTX-induced TLR4 activation.
- Computational models revealed PTX binds within the MD-2 pocket in both species, but differences in electrostatic potential, pocket size, and Phe(126) location explain species-specific TLR4 activation.
Conclusions:
- Paclitaxel (PTX) binds to both human and murine MD-2, but the interaction with murine MD-2 is critical for activating the TLR4 pathway.
- Species-specific differences in MD-2 structure, particularly involving Phe(126), dictate the ability of PTX to bridge MD-2 and TLR4 for dimerization and activation.
- Understanding these molecular interactions provides insights into the differential immune responses to PTX across species.
