Cryo-EM structure of a RAS/RAF recruitment complex

Area of Science:

• Molecular biology
• Cell signaling
• Structural biology

Background:

• RAF-family kinases initiate signaling via the MAP kinase cascade upon activation by GTP-bound RAS.
• Previous structural studies examined isolated RAS-binding and cysteine-rich domains of RAF, not intact BRAF.

Purpose of the Study:

• To determine the structural basis of RAS-BRAF interaction using intact BRAF.
• To investigate the role of membrane recruitment in BRAF activation by RAS.
• To explore potential therapeutic strategies targeting RAS-BRAF interactions.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structures.
• Complexes of KRAS bound to intact BRAF, MEK1, and a 14-3-3 dimer were analyzed.
• In vitro activation assays were performed to assess BRAF activity.

Main Results:

• Cryo-EM revealed structures of KRAS bound to intact BRAF in an autoinhibited state with MEK1 and 14-3-3.
• KRAS binds to the RAS-binding domain of BRAF in two distinct orientations.
• KRAS binding alone does not activate BRAF; membrane recruitment is essential.

Conclusions:

• RAS binding and BRAF activation are separable processes.
• Stabilizing the pre-activation KRAS/BRAF complex is a potential therapeutic strategy.
• Understanding RAS-BRAF complex structures provides insights into MAP kinase pathway regulation.