Discovering Targetable Conformation of RhoA Mutant by Integrating Native Mass Spectrometry, Ultraviolet Photodissociation, and X-ray Diffraction.

Pathogenic mutations in "undruggable" Ras superfamily proteins challenge drug development by inducing subtle, dynamic conformational changes. Here, we integrated X-ray crystallography with native mass spectrometry and ultraviolet photodissociation (nMS-UVPD) to reveal a cryptic conformation in the oncogenic Y42C mutant of RhoA. While crystallography alone resolved two ambiguous structures, nMS-UVPD determined the dominant conformation by directly mapping the mutant's conformational dynamics, identifying an enhanced Mg2+-locked conformation. We explored the mechanism of mutation impairing GTP hydrolysis. This state unmasks a previously hidden, druggable pocket adjacent to Cys42, guiding our identification of a covalent inhibitor. Our integrated approach establishes a roadmap for targeting pathogenic protein mutants previously considered "undruggable" due to their highly dynamic nature.