Rabs grab motors: defining the connections between Rab GTPases and motor proteins (original) (raw)
Related papers
Rabs and their effectors: Achieving specificity in membrane traffic
Proceedings of the National Academy of Sciences, 2006
Rab proteins constitute the largest branch of the Ras GTPase superfamily. Rabs use the guanine nucleotide-dependent switch mechanism common to the superfamily to regulate each of the four major steps in membrane traffic: vesicle budding, vesicle delivery, vesicle tethering, and fusion of the vesicle membrane with that of the target compartment. These different tasks are carried out by a diverse collection of effector molecules that bind to specific Rabs in their GTP-bound state. Recent advances have not only greatly extended the number of known Rab effectors, but have also begun to define the mechanisms underlying their distinct functions. By binding to the guanine nucleotide exchange proteins that activate the Rabs certain effectors act to establish positive feedback loops that help to define and maintain tightly localized domains of activated Rab proteins, which then serve to recruit other effector molecules. Additionally, Rab cascades and Rab conversions appear to confer directio...
Rab proteins: The key regulators of intracellular vesicle transport
Experimental Cell Research, 2014
Vesicular/membrane trafficking essentially regulates the compartmentalization and abundance of proteins within the cells and contributes in many signalling pathways. This membrane transport in eukaryotic cells is a complex process regulated by a large and diverse array of proteins. A large group of monomeric small GTPases; the Rabs are essential components of this membrane trafficking route. Most of the Rabs are ubiquitously expressed proteins and have been implicated in vesicle formation, vesicle motility/delivery along cytoskeleton elements and docking/fusion at target membranes through the recruitment of effectors. Functional impairments of Rabs affecting transport pathways manifest different diseases. Rab functions are accompanied by cyclical activation and inactivation of GTP-bound and GDP-bound forms between the cytosol and membranes which is regulated by upstream regulators. Rab proteins are characterized by their distinct sub-cellular localization and regulate a wide variety of endocytic, transcytic and exocytic transport pathways. Mutations of Rabs affect cell growth, motility and other biological processes.
Cellular functions of Rab GTPases at a glance
Journal of cell science, 2015
Rab GTPases control intracellular membrane traffic by recruiting specific effector proteins to restricted membranes in a GTP-dependent manner. In this Cell Science at a Glance and the accompanying poster, we highlight the regulation of Rab GTPases by proteins that control their membrane association and activation state, and provide an overview of the cellular processes that are regulated by Rab GTPases and their effectors, including protein sorting, vesicle motility and vesicle tethering. We also discuss the physiological importance of Rab GTPases and provide examples of diseases caused by their dysfunctions.
Traffic control: Rab GTPases and the regulation of interorganellar transport
News in Physiological Sciences, 2001
V iewed through a microscope, the architecture of a eukaryotic cell suggests the internal partitions of a complex building. Unlike inert walls, however, cellular membranes are highly dynamic structures. For example, the entire surface area of the plasma membrane turns over every hour in a typical cell. This turnover permits changes in the protein and lipid composition of cellular membranes and mediates transfer of soluble macromolecules among intracellular organelles. Multicellular organisms make extensive use of traffic to and from the plasma membrane to regulate systems physiology. For example, hormones are secreted by exocytosis in the afferent limb of endocrine signaling, glucose and water transporters are reversibly inserted into the plasma membrane in response to endocrine signaling, and adhesion molecules are translocated to the cell surface to mediate intercellular attachment. How eukaryotic cells maintain their structure in the face of this heavy traffic is a classic problem of cellular biology that is rapidly yielding its secrets; the identities of numerous components of the molecular machines that mediate vesicular transport are known, high resolution structures of several components are available, and the molecular physiology of these machines is now coming into focus. Rab GTPases are ubiquitous components of vesicle trafficking machines, with different Rab proteins regulating traffic between different intracellular compartments (Fig. 1). Here we review the current understanding of the structure and function of Rab proteins in relation to other components of trafficking machines.
Rab7b at the intersection of intracellular trafficking and cell migration
Communicative & Integrative Biology, 2015
Rab proteins are small GTPases essential for controlling and coordinating intracellular traffic. The small GTPase Rab7b regulates the retrograde transport from late endosomes toward the Trans-Golgi Network (TGN), and is important for the proper trafficking of several receptors such as Toll-like receptors (TLRs) and sorting receptors. We recently identified the actin motor protein myosin II as a new interaction partner for Rab7b, and found that Rab7b transport is dependent on myosin II. Interestingly, we also discovered that Rab7b influences the phosphorylation state of myosin II by controlling the activation status of the small GTPase RhoA. Consequently, Rab7b is important for the remodeling of actin filaments in processes such as stress fiber formation, cell adhesion, polarization and cell migration. Our finding that Rab7b can control actomyosin reorganization reveals yet another important role for Rab proteins, in addition to their already established role as master regulators of intracellular transport. Here we discuss our findings and speculate how they can explain the importance of Rab7b in dendritic cells (DCs).
Coordinated recruitment of Spir actin nucleators and myosin V motors to Rab11 vesicle membranes
eLife, 2016
There is growing evidence for a coupling of actin assembly and myosin motor activity in cells. However, mechanisms for recruitment of actin nucleators and motors on specific membrane compartments remain unclear. Here we report how Spir actin nucleators and myosin V motors coordinate their specific membrane recruitment. The myosin V globular tail domain (MyoV-GTD) interacts directly with an evolutionarily conserved Spir sequence motif. We determined crystal structures of MyoVa-GTD bound either to the Spir-2 motif or to Rab11 and show that a Spir-2:MyoVa:Rab11 complex can form. The ternary complex architecture explains how Rab11 vesicles support coordinated F-actin nucleation and myosin force generation for vesicle transport and tethering. New insights are also provided into how myosin activation can be coupled with the generation of actin tracks. Since MyoV binds several Rab GTPases, synchronized nucleator and motor targeting could provide a common mechanism to control force generati...
Journal of Biological Chemistry
Rab proteins occur in the cytosol bound to Rab-GDP dissociation inhibitor (GDI). We demonstrate here that cytosolic complexes of Rab9 bound to GDI represent a functional pool of Rab9 protein that can be utilized for transport from late endosomes to the trans Golgi network in vitro. Immunodepletion of GDI and Rab proteins bound to GDI led to the loss of cytosol activity; readdition of pure Rab9-GDI complexes fully restored cytosol activity. Delipidated serum albumin could solubilize prenylated Rab9 protein, but unlike Rab9-GDI complexes, Rab9-serum albumin complexes led to indiscriminate membrane association of Rab9 protein. Rab9 delivered to membranes by serum albumin was functional, but GDI increased the efficiency of Rab9 utilization, presumably because it suppressed Rab9 protein mistargeting. Finally, GDI inhibited transport of proteins from late endosomes to the trans Golgi network, likely because of its capacity to inhibit the membrane recruitment of cytosolic Rab9. These experiments show that GDI contributes to the selectivity of Rab9 membrane recruitment and presents functional Rab9 to the endosome-trans Golgi network transport machinery.
Current Biology, 2001
Many intracellular compartments, including MHC Results and discussion RILP requires GTP-Rab7 for clustering of late endosomes class II-containing lysosomes [1], melanosomes and lysosomes around the MTOC [2], and phagosomes [3], move along microtubules Rab7 specifically associates with late endosomal/lysoin a bidirectional manner and in a stop-and-go somal compartments [8-11] and might thus regulate motor fashion due to the alternating activities of a plusprotein recruitment to these compartments. In order to end directed kinesin motor and a minus-end identify Rab7 binding proteins involved in this process, directed dynein-dynactin motor [4]. It is largely an Epstein-Barr virus-transformed human B lymphocyte unclear how motor proteins are targeted cDNA library was screened by yeast two-hybrid assay. A specifically to different compartments. Rab GTPases protein was isolated that specifically interacted with acrecruit and/or activate several proteins involved in tive, GTP bound Rab7Q67L but not with inactive, GDP membrane fusion and vesicular transport [5, 6]. They bound Rab7T23N. The same protein (called RILP) was associate with specific compartments after isolated by Cantalupo et al. [7]. When overexpressed by activation, which makes Rab GTPases ideal nuclear microinjection of cDNA in Mel JuSo cells expresscandidates for controlling motor protein binding ing MHC class II-GFP, RILP induced a collapse of class to specific membranes. We and others [7] have II-containing lysosomal compartments (see Supplemenidentified a protein, called RILP (for Rab7tary material available with this article online). This effect interacting lysosomal protein), that interacts with could be inhibited by coexpression of dominant-negative active Rab7 on late endosomes and lysosomes. Rab7T22N (see Supplementary material). Expression of Here we show that RILP prevents further cycling of the C-terminal half of RILP (denoted ⌬N) resulted in a
Biophysical Analysis of the Interaction of Rab6a GTPase with Its Effector Domains
Journal of Biological Chemistry, 2008
Rab GTPases are key regulators of intracellular vesicular transport that control vesicle budding, cargo sorting, transport, tethering, and fusion. In the inactive (GDP-bound) conformation, Rab GTPases are targeted to intracellular compartments where they are converted into the active GTP-bound form and recruit effector domain containing proteins. Rab6a has been implicated in dynein-mediated vesicle movement at the Golgi apparatus and shown to interact with a plethora of effector proteins. In this study, we identify minimal Rab6a binding domains of three Rab6a effector proteins: PIST, BicaudalD2, and p150 glued. All three domains are >15-kDa fragments predicted to form coiled-coil structures that display no sequence homology to each other. Complex formation with BicaudalD2 and p150 has a moderate inhibitory effect on the intrinsic GTPase activity of Rab6a, while interaction with PIST has no influence on the hydrolysis rate. The effectors bind activated Rab6a with comparable affinities with K d values ranging from high nanomolar to low micromolar. Transient kinetic analysis revealed that effectors bind to Rab6a in an apparent single-step reaction characterized by relatively rapid on-and off-rates. We propose that the high off-rates of Rab6⅐effector complexes enable GTPase-activating protein-mediated net dissociation, which would not be possible if the off-rate were significantly slower. Vesicle-mediated transport between intracellular membrane-bound compartments of eukaryotic cells is essential for biosynthesis, secretion, endocytosis, cell differentiation, and growth. Transport involves sequestering of the cargo molecules into vesicles, vesicular budding, transport processes, and finally docking and fusion of vesicles at the target membrane (1). GTPases of the Rab family play a central role in the regulation of these processes by recruiting specific partner (effector) proteins (2). Like all other GTPases involved in regulatory processes, Rab proteins interconvert between active, GTP-bound forms that are capable of effector interactions, and inactive,