Utilizing TAPBPR for Peptide Loading, Dissociation, and Exchange on Plasma Membrane-Expressed MHC-I.

TAPBPR has previously been identified as a homolog of tapasin, though the two proteins serve as mutually exclusive peptide editors. While tapasin functions solely as a constituent of the peptide loading complex, TAPBPR can function alone and independently of other chaperones and cofactors. An additional characteristic of TAPBPR is its lack of an endoplasmic-reticulum retention motif, which enables it to leak to the surface of particular cell types when overexpressed as well as an ability to promote peptide exchange at the cell surface as a recombinant soluble protein. The aforementioned features of TAPBPR provide the protein with unique capabilities for the characterization of its function, as well as the ability to dissect other properties of peptide loading such as peptide affinity for major histocompatibility complex class I and immune response to the presentation of immunoreactive peptide. Here, we describe the key methods used to decorate cells with peptides, permitting the assessment of the function of TAPBPR and its variants: peptide loading, peptide dissociation, and peptide exchange assays. The use of these assays confers the ability to dissect the catalytic function of TAPBPR and its variants, as well as conducting subsequent experiments utilizing the efficient decoration of cells with immunoreactive peptide.