Delving into peptide specificity of NK inhibitory receptors

About This Grant

Project Summary Effector functions of NK cells are regulated through a balance of activating and inhibitory receptor interactions. NK inhibitory receptors of the Ly49 (mouse) and KIR (human) families have been well characterized with both Ly49C and KIR being dominant players in NK cell inhibition and licensing. Like many of the NK receptors, Ly49C and KIR binds to MHC Class I molecules to inhibit NK cell effector functions such as lysis of tumor target cells. The identified binding site for Ly49C and H-2Kb MHC class I occurs at the base of the MHC class I molecule with no direct contacts to the peptide MHC interface that binds T cell receptors. The binding site for KIR2DL3 for HLA- C1 has also been identified and there are crystal structures for both NK inhibitory receptors. As innate germline encoded receptor, Ly49C and KIR2DL3 binding to MHC class I molecules would be consistent with its function for assessing missing MHC on the target cell surface. However, early research discovered a puzzling level of peptide specificity to the molecules that regulated NK cell cytotoxicity. For Ly49C, a series of follow-up analyses has for the most part been unable to provide a clear explanation for the effects of peptide bound to MHC at a distinctly different site. Even crystallographic studies failed to identify peptide-dependent differences that could alter Ly49C interaction with MHC class I and NK cell biology. Based on our experience in assessing differential T cell receptor interactions with peptide:MHC, we propose to investigate whether differential bond lifetimes, and not affinity, explain the function of Ly49C and KIR inhibitory receptors to control NK cell function. Our preliminary findings have identified dramatic differences in the characteristics of the bond between Ly49C/KIR and their respective peptide:MHC molecules. Our proposal will build on this preliminary data to provide mechanistic clarity on how Ly49C or KIR2DL3 distinguishes different peptide:MHC molecules. These innovative insights into how NK inhibitory receptors can sense different peptides presented embedded in MHC class I would dramatically shift our understanding of their function from a simple on/off switch to a more sophisticated receptor system dependent on cellular forces to regulate NK cell function.