Tapasin(O15533:9606) is a type I transmembrane protein essential for the optimal expression of stable MHC class I molecules on host cell surface. Its helps the MHC class I molecules to remain in a peptide receptive state, avoiding irresversible denaturation.
HCMV encodes a protein termed US3(Q77G48) that directly binds and inhibits Tapasin(O15533:9606). US3(Q77G48) is also a transmembrane protein and the interaction with host tapasin occurs through their endoplasmic reticulum domain. The E3-19K(P04494) protein from adenovirus also inhibit the pathway, by preventing association of Tapasin(O15533:9606) with TAP.