Specific inhibition of GPI-anchored protein function by homing and self-association of specific GPI anchors

Abstract

The functional specificity conferred by glycophosphatidylinositol (GPI) anchors on certain membrane proteins may arise from their occupancy of specific membrane microdomains. We show that membrane proteins with noninteractive external domains attached to the same carcinoembryonic antigen (CEA) GPI anchor, but not to unrelated neural cell adhesion molecule GPI anchors, colocalize on the cell surface, confirming that the GPI anchor mediates association with specific membrane domains and providing a mechanism for specific signaling. This directed targeting was exploited by coexpressing an external domain-defective protein with a functional protein, both with the CEA GPI anchor. The result was a complete loss of signaling capabilities (through integrin–ECM interaction) and cellular effect (differentiation blockage) of the active protein, which involved an alteration of the size of the microdomains occupied by the active protein. This work clarifies how the GPI anchor can determine protein function, while offering a novel method for its modulation.

Sialic Acid on the Glycosylphosphatidylinositol Anchor Regulates PrP-mediated Cell Signaling and Prion Formation

“…Recent studies suggest that differential glycosylation of the GPI anchor can affect the properties of some proteins, including protein structure (24), membrane localization, and intracellular trafficking (25). Here we show that sialic acid in the GPI affected the composition of the membranes surrounding PrP followed by neuraminidase to remove sialic acid.…”

Requirement of Glycosylphosphatidylinositol Anchor of Cripto-1 for trans Activity as a Nodal Co-receptor

“…For example, GPI-anchored proteins predominantly localize in lipid raft microdomains on the plasma membrane, and the GPIanchored form of CR-1 is cleavable by the activity of mammalian phospholipases including GPI-phospholipase D, whereas transmembrane forms are not (22). Recent reports have shown that GPI-signal sequences and glycosylation can play a critical role as determinants of biological activity (38,39), suggesting that the structure of the GPI membrane anchor in conjunction with glycosylation could affect the biological function of membrane proteins. For example, N-glycosylation of mouse Nodal increases stability of the mature secreted form and thereby enhances the biological activity in vitro (40).…”

The GPI-anchoring of PrP

“…11,39 In a more daring concept it has also been proposed that different signal sequences can actually direct the addition of different types of GPI-anchors. 40,41 However, experimental proof of such a mechanism is still required.…”