Similarities and differences in tapasin interaction with disparate murine MHC class I allotypes (93.11)

Abstract

Abstract Tapasin is a key molecule in the major histocompatibility complex (MHC) class I peptide-loading complex. In this study, we first assessed the influence of the tapasin C-terminus on H2-Kb, -Kd, and -Ld in mouse cells. Truncated mouse tapasin (lacking the transmembrane and C-terminal region) was unable to associate with TAP or any of three murine MHC class I allotypes, and did not assist murine MHC class I folding and surface expression. A tapasin mutant with a single substitution in the C-terminus (K408W) increased the amount of Kd (but not Ld) in the open, peptide-free form, relative to wild type tapasin. We investigated whether Kd was also particularly responsive to other tapasin mutations, and found that a C95S substitution in tapasin also caused an elevation in open Kd (but not open Ld or Kb). Folded Kd was found to be amply present in association with wild type tapasin, and even more so with tapasin K408W and C95S. In summary, our results suggest that the C-terminus of mouse tapasin plays a vital role in the surface expression of murine MHC class I molecules, and that mouse MHC allotypes vary in their sensitivity to specific alterations in tapasin sequence and in their release from tapasin after folding. Overall, our results reveal new complexity in tapasin’s interactions with polymorphic MHC class I molecules. (NIH Grant GM57428)