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      Competition for access to the rat major histocompatibility complex class I peptide-loading complex reveals optimization of peptide cargo in the absence of transporter associated with antigen processing (TAP) association.

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          Abstract

          Major histocompatibility complex (MHC) class I molecules load peptides in the endoplasmic reticulum in a process during which the peptide cargo is normally optimized in favor of stable MHC-peptide interactions. A dynamic multimolecular assembly termed the peptide-loading complex (PLC) participates in this process and is composed of MHC class I molecules, calreticulin, ERp57, and tapasin bound to the transporter associated with antigen processing (TAP) peptide transporter. We have exploited the observation that the rat MHC class I allele RT1-Aa, when expressed in the rat C58 thymoma cell line, effectively competes and prevents the endogenous RT1-Au molecule from associating with TAP. However, stable RT1-Au molecules are assembled efficiently in competition with RT1-Aa, demonstrating that cargo optimization can occur in the absence of TAP association. Defined mutants of RT1-Aa, which do not allow formation of the PLC, fail to become thermostable in C58 cells. Wild-type RT1-Aa, which does allow PLC formation, also fails to become thermostable in this cell line, which carries the rat TAPB transporter that supplies peptides incompatible for RT1-Aa binding. Full optimization of RT1-Aa requires the presence of the TAP2A allele, which is capable of supplying suitable peptides. Thus, formation of the PLC alone is not sufficient for optimization of the MHC class I peptide cargo.

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          Author and article information

          Journal
          J. Biol. Chem.
          The Journal of biological chemistry
          American Society for Biochemistry & Molecular Biology (ASBMB)
          0021-9258
          0021-9258
          Apr 16 2004
          : 279
          : 16
          Affiliations
          [1 ] Division of Cell Biology and Immunology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.
          Article
          M400456200
          10.1074/jbc.M400456200
          14764587
          41a2b815-910b-4f99-a90a-647fedcdb467
          History

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