Amino acid sequences in the alpha 1 domain and not glycosylation are important in HLA-A2/beta 2-microglobulin association and cell surface expression.
The role of the single carbohydrate moiety present on the HLA-A2 molecule was studied by introducing several amino acid substitutions (by site-directed mutagenesis of the HLA-A2 gene) in the consensus glycosylation sequence Asn-X-Ser. Two different amino acid substitutions of the asparagine residue at position 86 (glutamine and aspartic acid) resulted in the synthesis of ca. 39,000-molecular-weight nonglycosylated heavy chains that were detected in the cytoplasm but not on the surface of mouse L-cell transfectants. However, a low level of surface expression was detected following transfection of human (rhabdomyosarcoma) cells or mouse L cells containing human beta 2-microglobulin. The defect in surface expression was not due to the absence of the glycan moiety, since the substitution of a glycine for a serine at amino acid 88 did not have the same drastic effect in the presence of human beta 2-microglobulin. These and other data suggest that the asparagine residue may play a critical role in the conformation of the HLA heavy chain and its interaction with beta 2-microglobulin. Immunofluorescence microscopy following permeabilization of the transfectants demonstrated that the unglycosylated HLA heavy chains are sequestered in an unidentified cellular compartment that is different from the Golgi structure.
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D006031:Glycosylation; D006680:HLA Antigens / Q000235:genetics; D015789:HLA-A2 Antigen; D006801:Humans; D051379:Mice; D009154:Mutation; D014162:Transfection; D001613:beta 2-Microglobulin / Q000378:metabolism*
D006680:HLA Antigens; D015789:HLA-A2 Antigen; D001613:beta 2-Microglobulin