Human RIPK3 maintains MLKL in an inactive conformation prior to cell death by necroptosis

Area of Science:

• Molecular and Cellular Biology
• Structural Biology
• Immunology

Background:

• Necroptosis, a programmed lytic cell death, is vital for host defense but implicated in inflammatory diseases.
• The pathway culminates in MLKL (mixed lineage kinase-like) pseudokinase activation by RIPK3 (receptor-interacting protein kinase 3).
• Understanding MLKL activation is key for therapeutic targeting, yet species-specific differences exist.

Purpose of the Study:

• To determine the structure of the human RIPK3 kinase domain alone and complexed with MLKL.
• To elucidate the molecular mechanisms of human MLKL activation by RIPK3.
• To investigate the structural basis for species specificity in RIPK3-MLKL interaction.

Main Methods:

• X-ray crystallography was employed to obtain high-resolution structures.
• Structural comparisons were made between human and mouse RIPK3:MLKL complexes.
• Mutagenesis studies identified key residues at the RIPK3:MLKL interface.

Main Results:

• The structures reveal distinct conformations of human RIPK3 compared to its mouse homolog.
• Human RIPK3 maintains MLKL in an inactive state through specific interactions prior to necroptosis induction.
• The C-lobe interface between RIPK3 and MLKL is critical for complex formation and human necroptotic signaling.

Conclusions:

• Structural insights explain how human RIPK3 inhibits MLKL activation.
• The identified RIPK3:MLKL interface residues highlight species-specific interactions.
• These findings provide a basis for developing targeted therapies for inflammatory diseases by modulating necroptosis.