Influence of intermolecular disulfide bonds on assembly of mouse MHC class I molecules (130.25)

Abstract

Abstract Within the major histocompatibility (MHC) class I peptide-loading complex, tapasin and ERp57 are joined by a stable disulfide bond which is necessary for the efficient assembly of MHC class I molecules. In our investigation of murine tapasin, we identified a large covalently bound complex involving wild type mouse tapasin and ERp57. This complex, which migrates at ~150 kDa, is noticeably larger than the 110 kDa tapasin-ERp57 complex previously identified in human cells. Additional data suggest that the mouse MHC class I molecule Kd may be a part of this ~150 kDa complex. In order to investigate the importance of tapasin-ERp57 disulfide bonding for the assembly of murine MHC class I molecules, we introduced a tapasin C95S mutant into tapasin knockout mouse fibroblasts. Although this tapasin mutant is unable to disulfide bond with ERp57, mouse tapasin C95S was found to maintain a non-covalent association with ERp57. Mutation of tapasin C95 impaired the maturation and stability of MHC class I Kd molecules to a greater extent than was previously observed for the human MHC class I molecule, B*4402. Furthermore, the maturation and stability of mouse MHC class I Kb molecules was also impaired in cells expressing mouse tapasin C95S. In total, these results highlight inter-species differences in the MHC class I assembly pathway and emphasize the importance of studying diverse MHC class I allotypes.