REFOLDING AND REASSEMBLY OF SEPARATE ALPHA-CHAINS AND BETA-CHAINS OF CLASS-II MOLECULES OF THE MAJOR HISTOCOMPATIBILITY COMPLEX LEADS TO INCREASED PEPTIDE-BINDING CAPACITY

Class II molecules of the major histocompatibility complex present antigenic peptides to helper T cells. These are heterodimeric glycoproteins consisting of one α and one β chain. Two different α/β heterodimeric conformations as well as the separate α and β chains bind specific peptides. The α chain is thought to have one and the β chain two intramolecular disulfide bonds. In the present study we have reduced these disulfide bonds in the murine major histocompatibility complex molecule I-A(d), which led to the release of bound peptides from all conformations and to unfolding of the separate chains. The separate α and β chains could be refolded to their native structure by reoxidation of the cysteines. Refolding was accompanied by reassembly of the separated chains to the α/β heterodimer. Both the separated α and β chains and the α/β heterodimer bound significantly higher amounts of antigenic peptide after reduction and reoxidation, as compared to the untreated protein.