Structural basis for ligand-mediated mouse GITR activation

Zhaocai Zhou, Yukiko Tone, Xiaomin Song, Keiji Furuuchi, James D. Lear, Herman Waldmann, Masahide Tone^,¶, Mark I. Greene^,¶, and Ramachandran Murali^,¶

Departments of Pathology and Laboratory Medicine and Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104; and Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, United Kingdom

Received for publication October 4, 2007.

Abstract: Glucocorticoid-induced TNF receptor ligand (GITRL) is a member of the TNF super family (TNFSF). GITRL plays an important role in controlling regulatory T cells. The crystal structure of the mouse GITRL (mGITRL) was determined to 1.8-Å resolution. Contrary to the current paradigm that all ligands in the TNFSF are trimeric, mGITRL associates as dimer through a unique C terminus tethering arm. Analytical ultracentrifuge studies revealed that in solution, the recombinant mGITRL exists as monomers at low concentrations and as dimers at high concentrations. Biochemical studies confirmed that the mGITRL dimer is biologically active. Removal of the three terminal residues in the C terminus resulted in enhanced receptor-mediated NF-B activation than by the wild-type receptor complex. However, deletion of the tethering C-terminus arm led to reduced activity. Our studies suggest that the mGITRL may undergo a dynamic population shift among different oligomeric forms via C terminus-mediated conformational changes. We hypothesize that specific oligomeric forms of GITRL may be used as a means to differentially control GITR receptor signaling in diverse cells.

Key Words: costimulation • oligomerization • regulatory • T cell • TNF

The authors declare no conflict of interest.

Data deposition: The atomic coordinates and structure factors have been deposited in the Protein Data Bank, wwww.pdb.org (PDB ID code 2Q8O).

This article contains supporting information online at www.pnas.org/cgi/content/full/0711206105/DC1.

^¶To whom correspondence may be addressed. E-mail: mtone{at}mail.med.upenn.edu, greene{at}reo.med.upenn.edu, or murali{at}xray.med.upenn.edu

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