Conversion of a PI-anchored protein to an integral membrane protein by a single amino acid mutation.
Qa-2, a cell-surface glycoprotein anchored by phosphatidylinositol (PI), is structurally related to the class I transplantation antigens H-2 K, D, and L, which are integral membrane glycoproteins. The predicted transmembrane segment of Qa-2 differs from those of H-2 K, D, and L by the presence of an aspartate in place of a valine at position 295. A single base change that replaced this aspartate with valine resulted in cell-surface Qa-2 molecules that were insensitive to hydrolysis by a PI-specific phospholipase C and more resistant to papain cleavage, properties shared by H-2D. Cells expressing Asp----Val mutant Qa-2 proteins were still able to attach a PI anchor to endogenous proteins such as Thy-1 and J11D. It therefore appears that this single amino acid change converts Qa-2 from a PI-linked form into an integral membrane protein.
Waneck
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Biogen Research Corporation, Cambridge, MA 02142.
Stein
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ME
Flavell
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RA
D000595:Amino Acid Sequence; D000954:Antigens, Surface / Q000235:genetics; D001224:Aspartic Acid; D002460:Cell Line; D004247:DNA / Q000235:genetics; D006183:H-2 Antigens; D006649:Histocompatibility Antigens / Q000235:genetics; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010206:Papain / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D013945:Thymoma; D013953:Thymus Neoplasms; D014162:Transfection; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism; D014633:Valine
D000954:Antigens, Surface; D006183:H-2 Antigens; D006649:Histocompatibility Antigens; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D010716:Phosphatidylinositols; C032907:Q surface antigens; D001224:Aspartic Acid; D004247:DNA; D010738:Type C Phospholipases; D010206:Papain; D014633:Valine