Structural basis for defects of Keap1 activity provoked by its point mutations in lung cancer

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key regulator of the cellular oxidative stress response.
• Kelch-like protein 1 (Keap1) acts as a repressor of Nrf2 through direct molecular interaction.

Purpose of the Study:

• To elucidate the molecular mechanism governing the Keap1-Nrf2 interaction.
• To provide a structural basis for the dysregulation of this interaction in disease.

Main Methods:

• X-ray crystallography was employed to resolve the structure of the Kelch/DGR and CTR domains of mouse Keap1.
• Peptide binding assays were performed using a peptide containing the Nrf2 ETGE motif.
• Analysis of somatic mutations and gene variations in human lung cancer cells.

Main Results:

• The crystal structure revealed a six-bladed beta propeller in Keap1, stabilized by extensive hydrogen bonds, essential for Nrf2 association.
• The Nrf2 ETGE motif peptide binds to the Keap1 beta propeller via electrostatic interactions with conserved arginine residues.
• Specific mutations (Glycine to Cysteine) in the Keap1 DGR domain were identified in lung cancer cells, reducing Keap1's affinity for Nrf2.

Conclusions:

• The study provides a detailed structural understanding of the Keap1-Nrf2 complex.
• Structural insights explain how mutations in Keap1 can lead to impaired repression of Nrf2.
• These findings offer a structural basis for understanding the gain of Nrf2 function observed in certain cancers due to Keap1 dysfunction.