Rabs

Abstract

In this chapter we will describe the Rab family of proteins, one of the most important molecular machines operating within the secretory pathway. Rab proteins (Ras-related proteins in brain) are evolutionary conserved regulators of membrane traffic. They are of key importance for proper functioning of the exocytic secretory pathway and endocytosis. In fact, Rabs seem to play a role in all events of intracellular transport, i.e. they take part in cargo selection and budding of vesicular (or tubular) structures in donor compartments, they regulate the transport of these membrane-bound structures along cytoskeletal tracks, they control their docking to the target membrane, and they are involved in the final fusion of donor and target membrane. Moreover, they guarantee that organelles keep their protein and lipid composition as well as their right position within the cell (Seabra et al. 2002; Grosshans etal. 2006). Whereas 11 Rabs have been described in Saccharomycescerevisiae, more than 70 Rabs and Rab-like proteins exist in mammals (Pereira-Leal and Seabra 2001; Gurkan et al. 2005). Consequently, together with the SNAREs the Rabs are the largest of the protein families involved in membrane trafficking.