No glycolipid anchors are added to Thy-1 glycoprotein in Thy-1-negative mutant thymoma cells of four different complementation classes.
Recent evidence shows that the mature Thy-1 surface glycoprotein lacks the C-terminal amino acids 113 to 143 predicted from the cDNA sequence and is anchored in the plasma membrane by a complex, phosphatidylinositol-containing glycolipid attached to the alpha-carboxyl group of amino acid 112. Here we studied the biosynthesis of Thy-1 in two previously described and two newly isolated Thy-1-deficient mutant cell lines. Somatic cell hybridization indicated that their mutations affected some processing step rather than the Thy-1 structural gene. The Thy-1 made by mutants of classes C, F, and H bound detergent but, in contrast to wild-type Thy-1, their detergent-binding moieties could not be removed by phospholipase C. In addition, tryptophan, which only occurs in position 124, was incorporated into Thy-1 of these mutants but not of wild-type cells. Last, the Thy-1 of wild-type but not mutant cells could be radiolabeled with [3H]palmitic acid. Together, these findings strongly suggest that mutants of classes C, F, and H accumulate a biosynthetic intermediate of Thy-1 which retains at least part of the hydrophobic C-terminal peptide. The Thy-1 of these mutants remained endoglycosidase H sensitive, suggesting that it accumulated in the rough endoplasmic reticulum or the Cis-Golgi. A different Thy-1 intermediate was found in a class B mutant cell line: the Thy-1 of this mutant was 2 kilodaltons smaller than the Thy-1 of other cell lines, did not bind detergent, and was rapidly secreted via a normal secretory pathway.
D000818:Animals; D000954:Antigens, Surface / Q000235:genetics*; D002872:Chromosome Deletion; D005816:Genetic Complementation Test; D006017:Glycolipids / Q000378:metabolism*; D008223:Lymphoma / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics*; D009154:Mutation; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D018800:Thy-1 Antigens; D013945:Thymoma / Q000276:immunology; D013953:Thymus Neoplasms / Q000276:immunology; D014364:Tryptophan / Q000378:metabolism
D000954:Antigens, Surface; D006017:Glycolipids; D008562:Membrane Glycoproteins; D010169:Palmitic Acids; D018800:Thy-1 Antigens; D019308:Palmitic Acid; D014364:Tryptophan