The tapasin-related protein (TAPBPR) binds MHC class I molecules (MHC I) with high affinity and functions in a similar fashion to tapasin in vitro, suggesting TAPBPR is an additional MHC I peptide editor.

We investigated the hypothesis that TAPBPR provides an additional layer of quality control by analysing whether TAPBPR influences MHC I peptide selection in vitro. We found TAPBPR :binds MHC I with much higher affinity than tapasin;enhances the ability of empty MHC I molecules to bind peptide;catalyses dissociation of peptides from peptide-MHC I complexes; edits the MHC I peptide repertoire via peptide exchange;can function with at least one HLA–B allotype, in addition to the two HLA-A allotypes that have been studied to date.Cumulatively our findings support the possibility that TAPBPR provides an additional quality control layer for at least some MHC I molecules