Related Experiment Video
Updated: Aug 8, 2026

Measuring TCR-pMHC Binding In Situ using a FRET-based Microscopy Assay
Published on: October 30, 2015
Roles for calreticulin and a novel glycoprotein, tapasin, in the interaction of MHC class I molecules with TAP
B Sadasivan1, P J Lehner, B Ortmann
1Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Abstract:
Assembly of MHC class I-beta 2 microglobulin (beta 2m) dimers in the endoplasmic reticulum involves two chaperones. Calnexin has previously been shown to interact with free class I heavy chains. Here, we show that the related chaperone, calreticulin, binds human class I-beta 2m dimers prior to peptide loading. Calreticulin remains associated with at least a subset of class I molecules when they, in turn, bind to TAP. Further evidence suggests that the interaction of class I-beta 2m dimers with TAP occurs via a novel uncharacterized 48 kDa glycoprotein, tapasin, which can bind independently to TAP and class I-beta 2m-calreticulin complexes. Tapasin is absent from the mutant cell line .220, in which class I-TAP association and peptide loading is defective.
Related Concept Videos
Microtubule Associated Proteins (MAPs)
Cotranslational Protein Translocation
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...
Tail-anchoring of Proteins in the ER Membrane
Protein Folding Quality Check in the RER
Protein Translocation Machinery on the ER Membrane
Sec61 protein conducting channel
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the translocon complex.
T Cell Activation and Clonal Selection
Naive T cells that have not yet encountered an antigen express two primary CD...

