title: Efficient glycosylphosphatidylinositol (GPI) modification of membrane proteins requires a C-terminal anchoring signal of marginal hydrophobicity.
abstract: Many plasma membrane proteins are anchored to the membrane via a C-terminal glycosylphosphatidylinositol (GPI) moiety. The GPI anchor is attached to the protein in the endoplasmic reticulum by transamidation, a reaction in which a C-terminal GPI-attachment signal is cleaved off concomitantly with addition of the GPI moiety. GPI-attachment signals are poorly conserved on the sequence level but are all composed of a polar segment that includes the GPI-attachment site followed by a hydrophobic segment located at the very C terminus of the protein. Here, we show that efficient GPI modification requires that the hydrophobicity of the C-terminal segment is "marginal": less hydrophobic than type II transmembrane anchors and more hydrophobic than the most hydrophobic segments found in secreted proteins. We further show that the GPI-attachment signal can be modified by the transamidase irrespective of whether it is first released into the lumen of the endoplasmic reticulum or is retained in the endoplasmic reticulum membrane.
authors.affiliation: Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University SE-106 91 Stockholm, Sweden.
authors.forename: Carmen
authors.initials: C
authors.lastname: Galian
authors.forename: Patrik
authors.initials: P
authors.lastname: Björkholm
authors.forename: Neil
authors.initials: N
authors.lastname: Bulleid
authors.forename: Gunnar
authors.initials: G
authors.lastname: von Heijne
mesh_terms: D019881:Aminoacyltransferases / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D021382:Protein Sorting Signals / Q000502:physiology*
chemical_list: D017261:Glycosylphosphatidylinositols; D008565:Membrane Proteins; D021382:Protein Sorting Signals; D019881:Aminoacyltransferases; C023175:transamidases