Deglucosylation of N-linked glycans is an important step in the dissociation of calreticulin-class I-TAP complexes.
Recent evidence indicates that newly synthesized major histocompatibility complex (MHC) class I proteins interact with calnexin, a transmembrane endoplasmic reticulum protein specific for certain glycoproteins bearing monoglucosylated glycans. Here, we studied the association of newly synthesized class I proteins with calreticulin, a soluble calnexin-related ER protein, in murine T cells. We found that, unlike calnexin-class I interactions, calreticulin assembly with class I proteins was markedly decreased in the absence of beta 2 microglobulin expression and that calreticulin associated with a subset of class I glycoforms distinct from those assembled with calnexin but similar to those bound to TAP (transporter associated with antigen processing) proteins. Finally, these studies show that deglucosylation of N-linked glycans is important for dissociation of class I proteins from both calreticulin and TAP and that the vast majority of newly synthesized class I proteins associated with calreticulin are simultaneously assembled with TAP. The data demonstrate that calnexin and calreticulin chaperones assemble with distinct MHC class I assembly intermediates in the ER and show that glycan processing is functionally coupled to release of MHC class I proteins from peptide transport molecules.
van Leeuwen
J E
JE
Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1360, USA.
Kearse
K P
KP
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D000906:Antibodies; D001324:Autoantigens / Q000302:isolation & purification / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D037281:Calnexin; D037282:Calreticulin; D004721:Endoplasmic Reticulum / Q000276:immunology; D006031:Glycosylation; D006183:H-2 Antigens / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D011485:Protein Binding; D012261:Ribonucleoproteins / Q000302:isolation & purification / Q000378:metabolism*; D013154:Spleen / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D000906:Antibodies; D001324:Autoantigens; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D006183:H-2 Antigens; D012261:Ribonucleoproteins; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; D037281:Calnexin