PMID: 18040044 , Related PDB ids: 2Q1M, 2R30, 2R32
Chattopadhyay K, Ramagopal UA, Mukhopadhaya A, Malashkevich VN, Dilorenzo TP, Brenowitz M, Nathenson SG, Almo SC
Assembly and structural properties of glucocorticoid-induced TNF receptor ligand: Implications for function.
Proc Natl Acad Sci U S A. 2007 Dec 4;104(49):19452-7. Epub 2007 Nov 26.
Glucocorticoid-induced TNF receptor ligand (GITRL), a recently identified member of the TNF family, binds to its receptor GITR on both effector and regulatory T cells and generates positive costimulatory signals implicated in a wide range of T cell functions. Structural analysis reveals that the human GITRL (hGITRL) ectodomain self-assembles into an atypical expanded homotrimer with sparse monomer-monomer interfaces. Consistent with the small intersubunit interfaces, hGITRL exhibits a relatively weak tendency to trimerize in solution and displays a monomer-trimer equilibrium not reported for other TNF family members. This unique assembly behavior has direct implications for hGITRL-GITR signaling, because enforced trimerization of soluble hGITRL ectodomain results in an approximately 100-fold increase in its receptor binding affinity and also in enhanced costimulatory activity. The apparent reduction in affinity that is the consequence of this dynamic equilibrium may represent a mechanism to realize the biologically optimal level of signaling through the hGITRL-GITR pathway, as opposed to the maximal achievable level.