Testing a chimeric molecule consisting of a SLA-1*0401 stalk and a HLA-A*11:01 peptide-binding platform-comparing human versus porcine β 2 m To test the proximal immunoglobulin-like membrane attaching SLA stalk, we generated recombinant porcine β 2 m and a chimeric human/porcine MHC-I heavy chain molecule where the α 1 α 2 were derived from the human HLA-A*11:01, and the α 3 was derived from the porcine SLA-1*0401. Since this construct contains the entire peptide-binding platform of HLA-A*11:01, we reasoned that the binding of the HLA-A*11:01 restricted peptide, KVFPYALINK, could be used as a functional readout of the refolding, activity, and assembly of the entire chimeric molecule including the porcine SLA stalk. For comparison, we tested the supportive capacity of human β 2 m and folding ability of the entirely human HLA-A*11:01. A total of four combinations could therefore be tested: porcine or human β 2 m in combination with either HHP or HHH (where the first letter indicates the origin of the α 1 domain (Human HLA-A*11:01 or Porcine SLA-1*0401), the second letter the origin of the α 2 domain, and the third letter the origin of the α 3 domain). A concentrationtitration of heavy chain was added to a fixed excess concentration (3 μM) of β 2 m and a fixed trace concentration (23 nM) of radiolabeled peptide. As shown in Figs. 4 and 5, the four combinations gave almost the same heavy chain dose titration with a half-saturation occurring around 1-2 nM heavy chain. Porcine β 2 m supported folding of the chimeric (HHP) α chain slightly better than it supported folding of the human (HHH) α chain. Human β 2 m supported folding of HHP and HHH equally well. Thus, a recombinant SLA stalk can fold and support peptide binding of the peptide-binding platform. These results also suggest that human β 2 m can support folding and peptide binding of porcine MHC-I heavy chain molecules.