The stability of R-spine defines RAF inhibitor resistance: A comprehensive analysis of oncogenic BRAF mutants with in-frame insertion of αC-β4 loop
Jiajun Yap, R. N. V. Krishna Deepak, Zizi Tian, Wan Hwa Ng, Kah Chun Goh, Alicia Foo, Zi Heng Tee, Manju Payini Mohanam, Yuen Rong M. Sim, Ufuk Degirmenci, Paula Yeng Po Lam, Zhongzhou Chen, Hao Fan, Jiancheng Hu
Abstract
) of αC-β4 loop. Using structure modeling and molecular dynamics simulation, we found that these insertions formed a large hydrophobic network that stabilizes R-spine and thus triggers the catalytic activity of BRAF. Furthermore, these insertions disrupted BRAF dimer interface and impaired dimerization. Unlike BRAF(V600E), these BRAF mutants with low dimer affinity were strongly resistant to all RAF inhibitors in clinic or clinical trials, which arises from their stabilized R-spines. As predicted by molecular docking, the stabilized R-spines in other BRAF mutants also conferred drug resistance. Together, our data indicated that the stability of R-spine but not dimer affinity determines the RAF inhibitor resistance of oncogenic BRAF mutants.