Calreticulin and calnexin interact with different protein and glycan determinants during the assembly of MHC class I.
Before peptide binding, a variety of endoplasmic reticulum (ER) proteins are associated with class I including calnexin, TAP, calreticulin, and tapasin. Although the selective functions of any one of these ER proteins have been difficult to define, individually or in combination they perform two general chaperone functions for class I. They promote assembly of the class I heterotrimeric molecule (heavy (H) chain, beta2m, and peptide) and they retain incompletely assembled complexes in the ER. In this study, we present evidence that calreticulin clearly differs from calnexin in how it associates with class I. Regarding the structural basis of the association, the oligosaccharide moiety in the alpha1 domain and the amino acid residue at position 227 in the alpha3 domain were both found to be critical for the interaction of class I with calreticulin. Interestingly, calreticulin displayed sensitivity to class I peptide binding even in TAP-deficient human or mouse cells. Thus, calreticulin is clearly more specific than calnexin in the structures and conformation of the class I molecule with which it can interact.
Harris
M R
MR
Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110, USA.
Yu
Y Y
YY
Kindle
C S
CS
Hansen
T H
TH
Solheim
J C
JC
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D017920:Antiporters / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D037281:Calnexin; D037282:Calreticulin; D002236:Carbohydrate Conformation; D000939:Epitopes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007136:Immunoglobulins / Q000378:metabolism; D007739:L Cells; D026901:Membrane Transport Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D010446:Peptide Fragments / Q000494:pharmacology; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism*
D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D017920:Antiporters; D002135:Calcium-Binding Proteins; D037282:Calreticulin; D000939:Epitopes; D015395:Histocompatibility Antigens Class I; D007136:Immunoglobulins; D026901:Membrane Transport Proteins; D010446:Peptide Fragments; D011134:Polysaccharides; D012261:Ribonucleoproteins; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; C107762:tapasin; D037281:Calnexin