Fig. 7: Structures represent distinct states of MHC-I and tapasin in the peptide loading pathway.

a cartoons representative of (left to right) MHC-I bound to low affinity (LA) peptide, MHC-I in complex with tapasin (peptide receptive (PR) state), and MHC-I bound to high affinity (HA) peptide. b examples of distinct states of MHC-I–β₂m and tapasin: 1, MHC-I immediately after biosynthesis, prior to engaging any peptide (represented by molecules immunoprecipitated by 64-3-7⁴⁹, which identifies the unfolded conformation of the α1 domain 3,10 helix⁵⁰); 2, MHC-I in conformed state bound to low affinity peptide (represented by our structure of HLA-B44:05-6mer (7TUD); 3, tapasin in state not yet engaged with MHC-I (represented by tapasin complexed with ERp57 (3F8U), with PaSta1 (7TUF), or with PaSta2 (7TUG)); 4, the MHC-I–tapasin complex (represented by 7TUE); 5, MHC-I bound to high affinity peptide, released from tapasin complex (represented by 7TUC). c cartoon description of the tapasin–MHC-I complex as part of the PLC, based on².