Kb, Kd, and Ld molecules share common tapasin dependencies as determined using a novel epitope tag.
The endoplasmic reticulum protein tapasin is considered to be a class I-dedicated chaperone because it facilitates peptide loading by proposed mechanisms such as peptide editing, endoplasmic reticulum retention of nonpeptide-bound molecules, and/or localizing class I near the peptide source. Nonetheless, the primary functions of tapasin remain controversial as do the relative dependencies of different class I molecules on tapasin for optimal peptide loading and surface expression. Tapasin dependencies have been addressed in previous studies by transfecting different class I alleles into tapasin-deficient LCL721.220 cells and then monitoring surface expression and Ag presentation to T cells. Indeed, by these criteria, class I alleles have disparate tapasin-dependencies. In this study, we report a novel and more direct method of comparing tapasin dependency by monitoring the ratio of folded vs open forms of the different mouse class I heavy chains, L(d), K(d), and K(b). Furthermore, we determine the amount of de novo heavy chain synthesis required to attain comparable expression in the presence vs absence of tapasin. Our findings show that tapasin dramatically improves peptide loading of all three of these mouse molecules.
Myers
N B
NB
Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA.
Harris
M R
MR
Connolly
J M
JM
Lybarger
L
L
Yu
Y Y
YY
Hansen
T H
TH
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D017920:Antiporters / Q000235:genetics / Q000502:physiology*; D001666:Binding Sites, Antibody; D001667:Binding, Competitive / Q000276:immunology; D002461:Cell Line, Transformed; D002474:Cell-Free System / Q000276:immunology / Q000378:metabolism; D000939:Epitopes / Q000235:genetics / Q000378:metabolism*; D006183:H-2 Antigens / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D064532:Histocompatibility Antigen H-2D; D006801:Humans; D007136:Immunoglobulins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D026901:Membrane Transport Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D010455:Peptides / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding / Q000276:immunology; D017510:Protein Folding
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D000939:Epitopes; D006183:H-2 Antigens; C024755:H-2K(K) antigen; C032876:H-2Kb protein, mouse; D064532:Histocompatibility Antigen H-2D; D007136:Immunoglobulins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010455:Peptides; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; C107762:tapasin