title: Modes of calreticulin recruitment to the major histocompatibility complex class I assembly pathway.
abstract: Major histocompatibility complex (MHC) class I molecules are ligands for T-cell receptors of CD8(+) T cells and inhibitory receptors of natural killer cells. Assembly of the heavy chain, light chain, and peptide components of MHC class I molecules occurs in the endoplasmic reticulum (ER). Specific assembly factors and generic ER chaperones, collectively called the MHC class I peptide loading complex (PLC), are required for MHC class I assembly. Calreticulin has an important role within the PLC and induces MHC class I cell surface expression, but the interactions and mechanisms involved are incompletely understood. We show that interactions with the thiol oxidoreductase ERp57 and substrate glycans are important for the recruitment of calreticulin into the PLC and for its functional activities in MHC class I assembly. The glycan and ERp57 binding sites of calreticulin contribute directly or indirectly to complexes between calreticulin and the MHC class I assembly factor tapasin and are important for maintaining steady-state levels of both tapasin and MHC class I heavy chains. A number of destabilizing conditions and mutations induce generic polypeptide binding sites on calreticulin and contribute to calreticulin-mediated suppression of misfolded protein aggregation in vitro. We show that generic polypeptide binding sites per se are insufficient for stable recruitment of calreticulin to PLC substrates in cells. However, such binding sites could contribute to substrate stabilization in a step that follows the glycan and ERp57-dependent recruitment of calreticulin to the PLC.
authors: Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors: Natasha
authors: N
authors: Del Cid
authors: Elise
authors: E
authors: Jeffery
authors: Syed Monem
authors: SM
authors: Rizvi
authors: Ericca
authors: E
authors: Stamper
authors: Larry Robert
authors: LR
authors: Peters
authors: William Clay
authors: WC
authors: Brown
authors: Chester
authors: C
authors: Provoda
authors: Malini
authors: M
authors: Raghavan
mesh_terms: D000818:Animals; D037282:Calreticulin / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002850:Chromatography, Gel; D005434:Flow Cytometry; D005822:Genetic Vectors; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011134:Polysaccharides / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D019704:Protein Disulfide-Isomerases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D013329:Structure-Activity Relationship
chemical_list: D037282:Calreticulin; D015395:Histocompatibility Antigens Class I; D011134:Polysaccharides; D019704:Protein Disulfide-Isomerases