Several patients with Mendelian susceptibility to mycobacterial diseases (MSMD) were shown to present a common mutation T168N creating an additional N-glycosylation site in the extracellular domain of the interferon γ receptor subunit IFNGR2 (Vogt et al., 2005)*. This inherited modification of the IFNGR2 subunit caused a complete lack of gene response to IFN-γ, a key cytokine for host defense, and resulted in children death.

In patient cells, IFN-γ-induced JAK/STAT signaling was fully inhibited. Spot variation fluorescence correlation spectroscopy (SvFCS) in live cells revealed that the IFNGR complex associates with membrane lipid nanodomains of the raft type upon IFN-γ stimulation. In contrast, the IFNGR2 T168N mutant did not associate with lipid nanodomains. Bioluminescence resonance energy transfer (BRET) experiments found a lack of IFNGR conformational change induced by IFN-γ binding and defects in JAK kinase association with IFNGR complex in patient cells. Removal of the extra glycan restores normal JAK/STAT signaling and IFN-γ biological activity. Proteomics analysis indicates that abnormal galectin binding to the mutated IFNGR2 subunit is responsible for these defects. Depletion of galectins restores normal IFNGR conformational change and JAK/STAT signaling in patient cells.

Our results provide the first positive evidence for the role of raft lipid nanodomains in IFNGR assembly and JAK/STAT signaling by IFN-γ in human cells. They also revealed the key role of receptor glycosylation and galectins in this process.

*Vogt, G., …., and J.L. Casanova. 2005. Gains of glycosylation comprise an unexpectedly large group of pathogenic mutations. Nat Genet. 37:692-700.