Construction of synthetic signals for glycosyl-phosphatidylinositol anchor attachment. Analysis of amino acid sequence requirements for anchoring.

Abstract

Many membrane proteins are anchored to the cell surface through covalent attachment to a glycosyl-phosphatidylinositol (GPI) structure. The GPI anchor is added to proteins in the endoplasmic reticulum following recognition of a signal in the COOH terminus of the protein. We show that the GPI anchoring signal can be completely recreated by the synthetic polymer Ser3-Thr8-Leu14, but not Thr11-Leu14, inserted at the COOH terminus of a protein. This is consistent with previous reports that a small amino acid such as Ser, Gly, or Ala, but not Thr, is required at the GPI attachment site. Analysis of synthetic amino acid sequences established a basic three-part signal for GPI anchoring: a cleavage/attachment domain that requires small amino acids at the first (GPI anchor attachment) and third positions but with little specificity at the middle position, a spacer domain of approximately 8-12 amino acids, and a hydrophobic domain of at least 11 amino acids. The ability to design a totally synthetic GPI anchoring signal will allow precise probing of the fine structure of this signal.