The immunological properties of endoplasmic reticulum chaperones: a conflict of interest?

ER chaperones are abundant and highly conserved proteins that display both peptide binding and chaperone activity. Of the family of chaperones present in the mammalian ER, GRP94 and calreticulin are apparently unique in their ability to elicit CD8+ T-cell responses against components of their bound-peptide pools. The ability of GRP94 and calreticulin to elicit CD8+ T-cell responses indicates that both proteins bind peptides suitable for assembly on to MHC class-I molecules. The capacity to function as molecular chaperones and as peptide-binding proteins capable of transferring, directly or indirectly, peptides on to class-I molecules, indicates that GRP94 and calreticulin participate in the regulation of both peptide and polypeptide traffic in the ER. Perspectives on the regulation of and interplay between the peptide binding and chaperone activity of GRP94 and calreticulin are discussed.