CARBOXYL-TERMINUS STRUCTURAL REQUIREMENTS FOR GLYCOSYL-PHOSPHATIDYLINOSITOL ANCHOR ADDITION TO CELL-SURFACE PROTEINS

Glycosyl phosphatidylinositol (GPI)-anchored proteins contain in their COOH-terminal region a peptide segment that is thought to direct glyc olipid addition. This signal has been shown to require a pair of small amino acids positioned 10-12 residues upstream of an hydrophobic C-te rminal domain. We analysed the contribution of the region separating t he anchor acceptor site and the C-terminal hydrophobic segment by intr oducing amino acid deletions and substitutions in the spacer element o f the GPI-anchored Thy-1 glycoprotein. Deletions of 7 amino acids in t his region, as well as the introduction of 2 charged residues, prevent ed the glycolipid addition to Thy-1, suggesting that the length and th e primary sequence of the spacer domain are important determinants in the signal directing GPI anchor transfer onto a newly synthesized poly peptide. Furthermore, we tested these rules by creating a truncated fo rm of the normally transmembranous Herpes simplex virus I glycoprotein D (gDI) and demonstrating that when its C-terminal region displays al l the features of a GPI-anchored protein, it is able to direct glycoli pid addition onto another cell surface molecule.