Figure 13-14. A postulated role of Rab proteins in facilitating the docking of transport vesicles.

Figure 13-14A postulated role of Rab proteins in facilitating the docking of transport vesicles

A GEF in the donor membrane recognizes a specific Rab protein and induces it to exchange GDP for GTP. GTP binding alters the conformation of the Rab protein, exposing a covalently attached lipid group, which helps anchor the protein in the membrane. Recall that an analogous mechanism helps to bind the coat-recruitment GTPases to these membranes, although a different GEF is involved (see Figure 13-10). The Rab-GTP remains bound to the surface of the transport vesicle after it pinches off from the donor membrane, and it then binds to varying Rab effector proteins on the target membrane. The Rab protein and its effectors help the vesicle dock and thereby facilitate the pairing of the appropriate v-SNAREs and t-SNAREs. After the vesicle has fused with the target membrane, the Rab protein hydrolyzes its bound GTP, releasing Rab-GDP into the cytosol, from where it can be reused in a new round of transport. As shown, Rab-GDP in the cytosol is bound to a GDP dissociation inhibitor (GDI), which prevents the Rab from releasing its bound GDP until it has interacted with appropriate proteins in the donor membrane. For clarity, we have omitted all of the proteins in the vesicle coats from this figure (see Figure 13-10).

From: The Molecular Mechanisms of Membrane Transport and the Maintenance of Compartmental Diversity

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 4th edition.
Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002.
Copyright © 2002, Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter; Copyright © 1983, 1989, 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson .

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.