Juxtamembrane basic residues in glycoprotein Ibβ cytoplasmic domain are required for assembly and surface expression of glycoprotein Ib-IX complex

Platelet glycoprotein (GP) Ib-IX complex requires all its three subunits for efficient expression on the cell surface, but the underlying molecular basis is not fully clear. Using transfected Chinese hamster ovary cells as the model system, we demonstrate that juxtamembrane residues 149-154 in the cytoplasmic domain of the GPIb beta subunit is required for assembly and surface expression of the GPIb-IX complex. The complex, or GPIbb by itself, lacking these residues is retained in the endoplasmic reticulum. Our results thus have illustrated an important role of the GPIbb cytoplasmic domain in biosynthesis of the GPIb-IX complex.