Newly assembled major histocompatibility complex (MHC) class I molecules, together with the endoplasmic reticulum chaperone Calreticulin [embl: M84739], interact with the transporter associated with antigen processing (TAP) through a molecule called Tapasin [emblnew: AF009510]. The molecular cloning of tapasin revealed it to be encoded by an MHC-linked gene. The cDNA encodes a 448-residue-long ORF, including a signal peptide. The protein is predicted to be a type I membrane glycoprotein with a cytoplasmic tail containing a double-lysine motif (-KKKAE-COOH) known to maintain membrane proteins in the endoplasmic reticulum. It is a member of the immunoglobulin superfamily. It has been suggested that a trimeric complex is formed consisting of TAP1, TAP2, and Tapasin which interacts transiently with class I HC/beta2-m during peptide binding. Up to four MHC class I-tapasin complexes are believed to bind to each TAP molecule.

Suggested further reading

Ortmann B, 1997
A critical role for tapasin in the assembly and function of multimeric MHC class I-TAP complexes.
Science 277(5330), 1306-1309 (1997)

Li S, 1997
Cloning and functional characterization of a subunit of the transporter associated with antigen processing.
Proc Natl Acad Sci U S A 94(16), 8708-8713 (1997)

Solheim JC, 1997
Prominence of beta 2-microglobulin, class I heavy chain conformation, and tapasin in the interactions of class I heavy chain with calreticulin and the transporter associated with antigen processing.
J Immunol 158(5), 2236-2241 (1997)