title: Bap29/31 influences the intracellular traffic of MHC class I molecules.
abstract: In this study, we examine the role of the putative cargo receptor B cell-associated protein (Bap)29/31 in the export of MHC class I molecules out of the endoplasmic reticulum (ER). We show that Bap31 binds to two allotypes of mouse class I molecules, with the interaction initiated at the time of H chain association with beta(2)-microglobulin and maintained until the class I molecule has left the ER. We also show that Bap31 is part of the peptide-loading complex, although is not required for its formation. Bap31 binds not only to class I molecules, but can bind to tapasin in the absence of class I. Consistent with an important role in recruiting class I molecules to transport vesicles, we show that in the absence of Bap29/31, there is a loss of class I colocalization with mSec31 (p137), a component of mammalian coat protein complex II coats. This observation is also associated with a delay in class I traffic from ER to Golgi. Our results are consistent with the view that class I molecules are largely recruited to ER exit sites by Bap29/31, and that Bap29/31 is a cargo receptor for MHC class I molecules.
authors.affiliation: Department of Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Marie-Eve
authors.initials: ME
authors.lastname: Paquet
authors.forename: Myrna
authors.initials: M
authors.lastname: Cohen-Doyle
authors.forename: Gordon C
authors.initials: GC
authors.lastname: Shore
authors.forename: David B
authors.initials: DB
authors.lastname: Williams
mesh_terms: D000818:Animals; D017920:Antiporters / Q000378:metabolism; D022181:COP-Coated Vesicles / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D007136:Immunoglobulins / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology; D026901:Membrane Transport Proteins; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D029701:Saccharomyces cerevisiae Proteins; D013234:Stem Cells; D033921:Vesicular Transport Proteins
chemical_list: D017920:Antiporters; C489641:Bcap29 protein, mouse; C489642:Bcap31 protein, mouse; D002352:Carrier Proteins; D015395:Histocompatibility Antigens Class I; D007136:Immunoglobulins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010750:Phosphoproteins; C106113:SEC31 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; C107762:tapasin