The glycan processing and siteoccupancy of recombinant Thy-1 is markedly affected by the presenceof a glycosylphosphatidylinositol anchor

Mercy Devasahayam2,3, PeterD. Catalino2,3, Pauline M. Rudd2, Raymond A. Dwek2 and A. Neil Barclay1,3

2 Oxford Glycobiology Institute,Department of Biochemistry, and 3 MRC CellularImmunology Unit, Sir William Dunn School of Pathology, Universityof Oxford, South Parks Road, Oxford, OX1 3QU, England

Received on April 22, 1999; revisedon June 22, 1999; accepted on June 28, 1999

Abstract

Thy-1 is a cell surface glycoprotein containing threeN-linked glycosylation sites and a glycosylphosphatidylinositol (GPI)anchor. The effect of the anchor on its N-linked glyco­sylationwas investigated by comparing the glycosylation of soluble recombinantThy-1 (sThy-1) with that of recombinant GPI anchored Thy-1, bothexpressed in Chinese hamster ovary cells. The sThy-1 was producedin a variety of isoforms including some which lacked carbohydrateon all three sequons whereas the GPI anchored form appeared fullyglycosylated like native Thy-1. This was surprising as the attachmentof N-linked sugars occurs cotranslationally and it was not expectedthat the presence of a C-terminal GPI anchor signal sequence wouldaffect sequon occupancy. Furthermore sThy-1 lacking glycosylationcould be produced with the inhibitor tunicamycin but in contrastcell surface expression of unglycosylated GPI anchored Thy-1 couldnot be obtained. The GPI anchored form appeared less processed withalmost 4-fold more oligo­mannose oligosaccharides thanin sThy-1 and also with less sialylated and core fucosylated biantennaryglycans. Possible mechanisms whereby the anchor or the anchor signalsequence, control site occupancy and maturation are discussed.

Key words: glycosylation/glycosylphosphatidylinositol anchor/sequonoccupancy/Thy-1

Footnotes

1 Towhom correspondence should be addressed Back