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Updated: Aug 9, 2026

Tandem Affinity Purification of Protein Complexes from Eukaryotic Cells
Published on: January 26, 2017
A critical role for tapasin in the assembly and function of multimeric MHC class I-TAP complexes
B Ortmann1, J Copeman, P J Lehner
1Howard Hughes Medical Institute, Section of Immunobiology, Yale University School of Medicine, 310 Cedar Street, New Haven, CT 06510, USA.
Tapasin is a crucial protein that facilitates the interaction between major histocompatibility complex (MHC) class I molecules and the transporter associated with antigen processing (TAP). Its expression restores normal antigen presentation and immune cell recognition in deficient cells.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Major histocompatibility complex (MHC) class I molecules present antigens to cytotoxic T lymphocytes.
- The transporter associated with antigen processing (TAP) is essential for loading peptides onto MHC class I molecules.
- Tapasin acts as a molecular bridge between MHC class I and TAP in the endoplasmic reticulum.
Purpose of the Study:
- To investigate the role of tapasin in the assembly and function of MHC class I peptide-loading complexes.
- To characterize the molecular properties and interactions of tapasin.
- To determine the functional significance of tapasin in antigen presentation and T cell recognition.
Main Methods:
- Molecular cloning and characterization of the tapasin gene.
- Analysis of protein-protein interactions using co-immunoprecipitation assays.
- Functional studies in a tapasin-deficient mutant cell line (220).
- Assessment of MHC class I surface expression and cytotoxic T cell recognition.
Main Results:
- Tapasin is a transmembrane glycoprotein encoded by an MHC-linked gene and belongs to the immunoglobulin superfamily.
- Tapasin forms stable complexes with MHC class I molecules and binds to TAP.
- Expression of tapasin in 220 cells restored MHC class I-TAP association and surface expression.
- Tapasin expression corrected the defective recognition of virus-infected cells by cytotoxic T cells.
Conclusions:
- Tapasin plays a critical role in the assembly and function of the MHC class I peptide-loading complex.
- Tapasin is essential for efficient MHC class I-restricted antigen processing and presentation.
- Tapasin is indispensable for proper immune surveillance by cytotoxic T lymphocytes.
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