title: Cutting edge: Tapasin is retained in the endoplasmic reticulum by dynamic clustering and exclusion from endoplasmic reticulum exit sites.
abstract: Tapasin retains empty or suboptimally loaded MHC class I molecules in the endoplasmic reticulum (ER). However, the molecular mechanism of this process and how tapasin itself is retained in the ER are unknown. These questions were addressed by tagging tapasin with the cyan fluorescent protein or yellow fluorescent protein (YFP) and probing the distribution and mobility of the tagged proteins. YFP-tapasin molecules were functional and could be isolated in association with TAP, as reported for native tapasin. YFP-tapasin was excluded from ER exit sites even after accumulation of secretory cargo due to disrupted anterograde traffic. Almost all tapasin molecules were clustered, and these clusters diffused freely in the ER. Tapasin oligomers appear to be retained by the failure of the export machinery to recognize them as cargo.
authors.affiliation: Department of Biology, The Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: Tsvetelina
authors.initials: T
authors.lastname: Pentcheva
authors.forename: Elias T
authors.initials: ET
authors.lastname: Spiliotis
authors.forename: Michael
authors.initials: M
authors.lastname: Edidin
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D004058:Diffusion; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007136:Immunoglobulins / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D008856:Microscopy, Fluorescence; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D001426:Bacterial Proteins; D007136:Immunoglobulins; D008164:Luminescent Proteins; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; C073119:TAP1 protein, human; C107762:tapasin; C054562:yellow fluorescent protein, Bacteria