Structures of mouse and human GITR-GITRL complexes reveal unique TNF superfamily interactions

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• Glucocorticoid-induced tumor necrosis factor receptor (GITR) and GITR ligand (GITRL) are key regulators of immune responses within the tumor necrosis superfamily.
• GITR is a therapeutic target for modulating T cell activity and promoting anti-tumor immunity.
• Understanding the structural basis of GITR-GITRL interaction is essential for designing effective immunotherapies.

Purpose of the Study:

• To determine the structures of human and mouse GITR receptors bound to their cognate ligands.
• To elucidate the molecular mechanisms underlying GITR-GITRL interactions and higher-order complex formation.
• To investigate the functional consequences of altering the GITR-GITRL interface on cell signaling.

Main Methods:

• X-ray crystallography to determine the structures of GITR-GITRL complexes.
• In vitro ligand binding assays to assess the impact of interface mutations on binding affinity.
• Cell imaging experiments using fluorescently labeled ligands to visualize membrane complex formation.

Main Results:

• The structures reveal conserved receptor-ligand and receptor-receptor interfaces between human and mouse GITR-GITRL complexes.
• Human GITR-GITRL can form hexameric membrane networks, while murine GITR-GITRL forms linear chains.
• Mutations at the human GITR receptor-receptor interface decrease cell signaling and higher-order membrane structure formation.

Conclusions:

• The unique C-terminal receptor-receptor interface enables distinct higher-order structures of GITR-GITRL complexes on cell membranes.
• These structural insights provide a foundation for developing targeted therapies that modulate GITR signaling for cancer treatment.
• Understanding the species-specific assembly of GITR-GITRL complexes is critical for preclinical translation of GITR-based immunotherapies.