The structural and mechanistic basis for recycling of Rab proteins between membrane compartments

Abstract

Rab proteins are members of the Ras superfamily of GTPases and are key regulators of intracellular vesicular transport. They undergo a cycle of GTPase activity, and this activity is interconnected to a cycle of reversible attachment to membranes. This cycle is mediated by geranylgeranylation of (usually) two C-terminal cysteines, which in turn is effected by Rab geranylgeranyltransferase in concert with REP (Rab escort protein). After delivery to their respective membranes, Rabs are activated by replacement of GDP by GTP, allowing interaction with a wide variety of effector molecules involved in vesicular transport, in particular with docking of transport vesicles to their specific target membranes. After completion of these events and GTP hydrolysis, Rabs are retrieved by GDI (GDP dissociation inhibitor) and delivered to their starting compartment. Here, the structural and mechanistic basis of events occurring in Rab delivery and cycling, and the differences between REP and GDI are discussed on the basis of recent advances in the field.

α-Synuclein Membrane Association Is Regulated by the Rab3a Recycling Machinery and Presynaptic Activity*

“…Depolarization-induced Ca 2ϩ influx activates GTP cleavage by membrane-bound Rab3a, followed by the retrieval of GDP-Rab3a by a GDI⅐Hsp90 complex (20,47). The ␣-syn⅐Rab3a complex raised the possibility that the guanine nucleotide-dependent Rab3a conformation may also influence ␣-syn distribution.…”

Membrane recruitment of the cargo-selective retromer subcomplex is catalysed by the small GTPase Rab7 and inhibited by the Rab-GAP TBC1D5

“…The interaction between VPS35/29/26 and Rab7 is substoichiometric, which is consistent with a transient and/or dynamic interaction. Mass spectrometric analysis of the large-scale native immunoprecipitations confirmed that the VPS35/29/26 complex interacts with Rab7 and also indicated that the interaction is likely to be direct, because the only other proteins that were detected in the GFP-Rab7 immunoprecipitation lane were Rab escort protein-1 and GDI-1 and GDI-2, both of which are involved in maintaining the cytosolic Rab7 in a soluble form (Goody et al, 2005). We did not observe a band corresponding to VPS29 in the native immunoprecipitation samples, possibly because the silver stain used to visualise the bands does not stain the VPS29 protein.…”

Nucleotide-dependent farnesyl switch orchestrates polymerization and membrane binding of human guanylate-binding protein 1

“…This mechanism is crucially different for hGBP1 and resembles that of N-terminally myristoylated Arf proteins (36). Human GBP1 F attaches to the membrane upon GTP binding and leaves the membrane as a soluble protein when no more GTP is available, obviously not requiring any helper protein for positioning its farnesyl anchor inaccessible for other interaction partners (like the membrane) as is the case for small Ras-like Rho and Rab GTPases (35). Thus, we report that the accessibility of an isoprenyl anchor from a GTP-binding protein is exclusively controlled by the associated nucleotide.…”

“…Many examples of Ras-like proteins show nucleotide-dependent shuttling between various membrane compartments, e.g., the GTP-binding and hydrolysis-driven function of Rab proteins is the traveling between organelles and thereby directing the transport of cargo. These cycles of membrane binding and dissociation are facilitated by specific helper proteins [guanine-nucleotide dissociation inhibitors (GDIs)], which take up the isoprenyl anchor in a binding pocket to enable the GTP-binding protein to leave the membrane and travel through the cytosol (35). This mechanism is crucially different for hGBP1 and resembles that of N-terminally myristoylated Arf proteins (36).…”