Abstract
Tapasin forms a bridge between TAP (transporters associated with antigen processing) and MHC class I molecules and plays a critical role in class I assembly. In its absence, TAP and class I do not associate, and class I cell surface expression is reduced. We now identify two independent functions for tapasin. Tapasin increases TAP levels and allows more peptide to be translocated to the endoplasmic reticulum. Furthermore, when expressed in the tapasin-negative .220 cell line, recombinant soluble tapasin retains its association with class I and restores class I cell surface expression and function, even though it no longer binds TAP or increases TAP levels. This finding suggests that the association of tapasin with class I is sufficient to facilitate loading and assembly of class I molecules.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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ATP Binding Cassette Transporter, Subfamily B, Member 2
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ATP Binding Cassette Transporter, Subfamily B, Member 3
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ATP-Binding Cassette Transporters / metabolism*
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Antigen Presentation*
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Antiporters / genetics
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Antiporters / metabolism*
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Biological Transport
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Endoplasmic Reticulum / metabolism
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HLA-B8 Antigen / metabolism*
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Humans
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Immunoglobulins / genetics
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Immunoglobulins / metabolism*
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Membrane Transport Proteins
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Mutation
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Peptides / metabolism*
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Protein Binding
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Solubility
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T-Lymphocytes, Cytotoxic / immunology
Substances
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ATP Binding Cassette Transporter, Subfamily B, Member 2
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ATP Binding Cassette Transporter, Subfamily B, Member 3
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ATP-Binding Cassette Transporters
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Antiporters
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HLA-B8 Antigen
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Immunoglobulins
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Membrane Transport Proteins
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Peptides
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TAP1 protein, human
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tapasin
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TAP2 protein, human