RabGEFs are a major determinant for specific Rab membrane targeting

Abstract

Analysis of three different Rab-RabGEF pairs reveals that RabGEFs contain the minimal targeting machinery for recruiting Rabs to specific membranes.

Mechanisms of action of Rab proteins, key regulators of intracellular vesicular transport

“…It was found that such constructs could all be prenylated after microinjection into cells, as long as the distance between the CIM and the C-terminal cysteines as well as the distance between the GTPase core structure and the CIM were kept at a proper length. Such Rab1 and Rab5 constructs were found to localize to the correct membranes, showing that the sequence of the C-terminus is not important for targeting of these GTPases, against the prediction that would have been made from early work (Chavrier et al, 1991) but in line with the results obtained on redirecting these proteins to mitochondria (Blumer et al, 2013). However, in the case of Rab35, correct localization to the plasma membrane was not seen using constructs in which the polybasic C-terminus was replaced by uncharged structural elements, suggesting a required interaction with the negatively charged membrane.…”

“…the ability to mediate dissociation of Rab : GDI and Rab : REP complexes by catalyzing GTP/GDP exchange on spontaneously dissociating Rab : GDP. The evidence presented on DrrA was of importance in the design of the experiments described above on Rab targeting (Blumer et al, 2013).…”

“…The work discussed above, together with other work described below on the influence of bacterial effector molecules on Rab localization, led to experiments designed to test the hypothesis that GEFs are involved in and perhaps responsible for guiding Rabs to their initial target membranes. The concept was to ectopically mislocalize RabGEFs to membranes where they are not normally found and to determine whether this then leads to mislocalization of their cognate Rabs to the same membrane (Blumer et al, 2013). The cell organelle chosen for this study was the mitochondrion, since there is relatively little Rab activity at the outer After ribosomal synthesis, an unprenylated Rab initially binds to the Rab escort protein (REP), which presents the Rab to Rab geranylgeranyltransferase (RabGGTase, consisting of an α-subunit and the catalytic β-subunit).…”

The role of the hypervariable C-terminal domain in Rab GTPases membrane targeting

“…GEF-mediated nucleotide exchange provides the thermodynamic driving force for Rab membrane insertion, which is indispensable for the stable attachment of Rabs to membranes (15,34,35). GEFs and GAPs appear to regulate Rab localization, because the nucleotide-bound state defines Rab membrane association (15).…”

Sorting of lipidated cargo by the Arl2/Arl3 system

“…58 Localized activation should be a more general principle of the function of small G proteins, and is for example described for the Rab proteins, where the localization of GEF is responsible for the localized activation of a specific Rab and the initiation of specific transport processes. 59 The same is true for the activation of Rho proteins which require a distinct localization of a particular Rho-GEF and a halo of a particular Rho-GAP around the area of activation, in order to induce locally defined and directed membrane deformations such as neurite protrusions or filopodia. 60 A good example of temporal hierarchical regulation of the GTPase cycle has been demonstrated for the entry of Salmonella typhimurium into cells.…”