An engineered protein antagonist of K-Ras/B-Raf interaction

Area of Science:

• Oncology
• Molecular Biology
• Protein Engineering

Background:

• Ras proteins are critical regulators of cell signaling, and their mutants drive approximately 30% of human cancers.
• Mutant Ras proteins often confer resistance to conventional cancer therapies.
• Targeting oncogenic Ras mutations presents a significant challenge in cancer treatment.

Purpose of the Study:

• To engineer a protein scaffold with high affinity and specificity for the oncogenic K-Ras G12D mutant.
• To elucidate the structural basis for the inhibitor's specificity towards mutant K-Ras.
• To evaluate the functional impact of the inhibitor on Ras-mediated signaling pathways.

Main Methods:

• Protein engineering to develop a K-Ras G12D-specific scaffold (R11.1.6).
• Co-crystallography to determine the structures of R11.1.6 bound to K-Ras WT and K-Ras G12D.
• Biochemical assays to assess binding affinity and specificity.
• Cellular assays to measure inhibition of the Raf/MEK/ERK signaling pathway.

Main Results:

• Engineered protein R11.1.6 exhibits nanomolar affinity for K-Ras G12D, with high specificity over wild-type K-Ras.
• Crystal structures reveal that differences in the switch I conformation are key to R11.1.6's specific binding.
• R11.1.6 directly inhibits K-Ras interaction with Raf, reducing downstream signaling via the Raf/MEK/ERK pathway.
• An extensive hydrophobic interface between K-Ras G12D and R11.1.6 was identified, distinct from polar Ras/effector interfaces.

Conclusions:

• The protein scaffold R11.1.6 represents the first inhibitor with high affinity and specificity for K-Ras G12D.
• Structural insights highlight the importance of the switch I conformation for K-Ras mutant targeting.
• This work provides a novel tool for Ras biology research and a template for developing non-covalent inhibitors against oncogenic Ras mutants.