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Crystal Structures of Human MdmX (HdmX) in Complex with p53 Peptide Analogues Reveal Surprising Conformational
Joerg Kallen1, Arnaud Goepfert, Anke Blechschmidt
1Novartis Institutes for BioMedical Research, CH-4002 Basel, Switzerland. joerg.kallen@novartis.com
Abstract:
p53 tumor suppressor activity is negatively regulated through binding to the oncogenic proteins Hdm2 and HdmX. The p53 residues Leu(26), Trp(23), and Phe(19) are crucial to mediate these interactions. Inhibiting p53 binding to both Hdm2 and HdmX should be a promising clinical approach to reactivate p53 in the cancer setting, but previous studies have suggested that the discovery of dual Hdm2/HdmX inhibitors will be difficult. We have determined the crystal structures at 1.3 A of the N-terminal domain of HdmX bound to two p53 peptidomimetics without and with a 6-chlorine substituent on the indole (which binds in the same subpocket as Trp(23) of p53). The latter compound is the most potent peptide-based antagonist of the p53-Hdm2 interaction yet to be described. The x-ray structures revealed surprising conformational changes of the binding cleft of HdmX, including an "open conformation" of Tyr(99) and unexpected "cross-talk" between the Trp and Leu pockets. Notably, the 6-chloro p53 peptidomimetic bound with high affinity to both HdmX and Hdm2 (K(d) values of 36 and 7 nm, respectively). Our results suggest that the development of potent dual inhibitors for HdmX and Hdm2 should be feasible. They also reveal possible conformational states of HdmX, which should lead to a better prediction of its interactions with potential biological partners.
Insights
Developing dual inhibitors for HdmX and Hdm2 to reactivate the p53 tumor suppressor is feasible. A novel 6-chloro p53 peptidomimetic shows high affinity for both HdmX and Hdm2, suggesting a promising clinical approach.
Area of Science:
- Oncology
- Structural Biology
- Drug Discovery
Background:
- p53 tumor suppressor activity is inhibited by oncogenic proteins Hdm2 and HdmX.
- Key p53 residues (Leu26, Trp23, Phe19) mediate these inhibitory interactions.
- Developing dual Hdm2/HdmX inhibitors to restore p53 function in cancer has been challenging.
Purpose of the Study:
- To investigate the feasibility of developing dual Hdm2/HdmX inhibitors.
- To characterize the binding of p53 peptidomimetics to HdmX using structural biology.
- To identify potent antagonists for reactivating p53 in cancer therapy.
Main Methods:
- Determined crystal structures of the HdmX N-terminal domain bound to two p53 peptidomimetics at 1.3 Å resolution.
- Utilized X-ray crystallography to analyze protein-ligand interactions and conformational changes.
- Measured binding affinities (Kd values) of peptidomimetics to HdmX and Hdm2.
Main Results:
- A 6-chloro p53 peptidomimetic demonstrated high affinity for both HdmX (Kd = 36 nM) and Hdm2 (Kd = 7 nM).
- This compound is the most potent peptide-based antagonist of the p53-Hdm2 interaction reported to date.
- Crystal structures revealed conformational changes in HdmX, including an "open conformation" of Tyr99 and cross-talk between binding pockets.
Conclusions:
- Development of potent dual inhibitors targeting HdmX and Hdm2 is feasible.
- The identified 6-chloro p53 peptidomimetic represents a promising lead compound for cancer therapy.
- Understanding HdmX conformational states can improve predictions of its biological interactions.
