Structure-function analysis of the SHOC2-MRAS-PP1C holophosphatase complex

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Receptor tyrosine kinase (RTK)-RAS signaling, involving the mitogen-activated protein kinase (MAPK) cascade, controls cell proliferation and survival.
• The SHOC2-MRAS-PP1C holophosphatase complex is crucial for RTK-RAS signaling by dephosphorylating RAF proteins, thereby activating MAPK signaling.
• Germline gain-of-function mutations in this complex cause RASopathy syndromes, but its structure and assembly remain unclear.

Purpose of the Study:

• To elucidate the structure and assembly of the SHOC2-MRAS-PP1C holophosphatase complex.
• To define the biophysical principles governing holoenzyme interactions and complex assembly order.
• To investigate the functional impact of SHOC2 variants using deep mutational scanning.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine the high-resolution structure of the SHOC2-MRAS-PP1C complex.
• Deep mutational scanning was performed to assess the functional consequences of numerous SHOC2 missense variants.
• Biophysical techniques were used to analyze holoenzyme interactions and assembly.

Main Results:

• The study resolved the structure of the SHOC2-MRAS-PP1C complex, detailing interactions between SHOC2, MRAS, and PP1C.
• SHOC2 interacts with MRAS and PP1C via its leucine-rich repeat region and N-terminal disordered region, respectively.
• Complex assembly initiates with SHOC2-PP1C binding, stabilized by GTP-loaded MRAS, explaining how RASopathy mutations enhance activity.

Conclusions:

• This work provides a comprehensive structure-function model of the SHOC2-MRAS-PP1C holophosphatase complex.
• The findings clarify how mutations associated with RASopathies and cancer enhance complex activity.
• The detailed understanding of binding interactions may guide the development of targeted therapeutics.