A Dominant Negative Mutant β2-Microglobulin Blocks the Extracellular Folding of a Major Histocompatibility Complex Class I Heavy Chain

The major histocompatibility complex class I (MHC1) molecule plays a crucial role in cytotoxic lymphocyte function. β2-Microglobulin (β2m) has been demonstrated to be both a structural component of the MHC1 complex and a chaperone-like molecule for MHC1 folding. β2m binding to an isolated α3 domain of MHC1 heavy chain at micromolar concentrations has been shown to accurately model the biochemistry and thermodynamics of β2m-driven MHC1 folding. These results suggested a model in which the chaperone-like role of β2m is dependent on initial binding to the α3 domain interface of MHC1 with β2m. Such a model predicts that a mutant β2m molecule with an intact MHC1 α3 domain interaction but a defective MHC1 α1α2 domain interaction would block β2m-driven folding of MHC1. In this study we generated such a β2m mutant and demonstrated that it blocks MHC1 folding by normal β2m at the expected micromolar concentrations. Our data support an initial interaction of β2m with the MHC1 α3 domain in MHC1 folding. In addition, the dominant negative mutant β2m can block T-cell functional responses to antigenic peptide and MHC1.