Viral US3 (green) degrades PDI (red) to thwart antigen presentation.
AHN/ELSEVIER
When scientists think of the immune system's antigen selection procedure, oxidation/reduction is just about the last thing to come to mind. Yet the group now shows that an oxidation step by protein disulfide isomerase (PDI) helps load antigenic peptides into MHC class I molecules, which then present the antigen on the cell surface.
PDI is best known as a chaperone, but the authors found it associated with ER proteins that pull antigens into the ER from the cytosol. Its chaperone activity seems to be intact here: it binds strongly to antigens and probably protects them from the abundant ER proteases. But PDI's role goes beyond chaperone duties.
PDI also regulates a disulfide bond...
