Suzanne R Pfeffer

Stanford University | SU · Department of Biochemistry

Parkinson’s disease-associated, activating mutations in LRRK2 kinase block primary cilia formation in cell culture and in specific cell types in the brain. In the striatum that is important for movement control, about half of astrocytes and cholinergic interneurons, but not the predominant medium spiny neurons, lose their primary cilia. Here we sho...

Mutations in LRRK2 and PINK1 are associated with familial Parkinson’s disease (PD). LRRK2 phosphorylates Rab GTPases within the Switch II domain whilst PINK1 directly phosphorylates Parkin and ubiquitin and indirectly induces phosphorylation of a subset of Rab GTPases. Herein we have crossed LRRK2 [R1441C] mutant knock-in mice with PINK1 knock-out...

Activating mutations in leucine-rich repeat kinase 2 (LRRK2) represent the most common cause of monogenic Parkinson's disease. LRRK2 is a large multidomain protein kinase that phosphorylates a specific subset of the ∼65 human Rab GTPases, which are master regulators of the secretory and endocytic pathways. After phosphorylation by LRRK2, Rabs lose...

Activating LRRK2 mutations cause Parkinson’s disease. Previously, we showed that cholinergic interneurons and astrocytes but not medium spiny neurons of the dorsal striatum lose primary cilia in LRRK2 mutant mice. Single nucleus RNA sequencing shows that cilia loss in cholinergic interneurons correlates with higher LRRK2 expression and decreased gl...

We demonstrate that the Parkinson’s VPS35[D620N] mutation alters the expression of ~220 lysosomal proteins and stimulates recruitment and phosphorylation of Rab proteins at the lysosome. This recruits the phospho-Rab effector protein RILPL1 to the lysosome where it binds to the lysosomal integral membrane protein TMEM55B. We identify highly conserv...

There exist at least three different pools of cholesterol in the plasma membrane: the essential pool, the sphingomyelin-sequestered pool, and the accessible pool (Radhakrishnan et al, 2020). Ciliary Hedgehog signaling is regulated by the accessible pool of cholesterol (Kinnebrew et al, 2019), and His-mNeon-FLAG-ALOD4, a toxin-based probe, can be us...

PPM1H phosphatase reverses Parkinson’s disease-associated, Leucine Rich Repeat Kinase 2-mediated Rab GTPase phosphorylation. We show here that PPM1H relies on an N-terminal amphipathic helix for Golgi localization. The amphipathic helix enables PPM1H to bind to liposomes in vitro, and small, highly curved liposomes stimulate PPM1H activity. We arti...

Activating mutations in the Leucine Rich Repeat Kinase 2 (LRRK2) cause Parkinson's disease. LRRK2 phosphorylates a subset of Rab GTPases, particularly Rab10 and Rab8A, and we showed previously that these phosphoRabs play an important role in LRRK2 membrane recruitment and activation (Vides et al., 2022). To learn more about LRRK2 pathway regulation...

Mutations in LRRK2 cause inherited Parkinson's disease. LRRK2 phosphorylates a subset of the Rab GTPase family and alters their effector interactions. PPM1H phosphatase counteracts LRRK2 signaling by specifically dephosphorylating Rab proteins at their LRRK2 phosphorylation site. PPM1H localizes to the surface of the Golgi via and N-terminal amphip...

Background: The endo-lysosomal phospholipid, bis(monoacylglycerol)phosphate (BMP), is aberrantly high in the urine of Parkinson's patients with mutations in genes encoding leucine-rich repeat kinase 2 (LRRK2) and glucocerebrosidase (GCase). Because BMP resides on and regulates the biogenesis of endo-lysosomal intralumenal membranes (exosomes when r...

PPM1H phosphatase reverses Parkinson’s disease-associated, LRRK2-mediated Rab GTPase phosphorylation. We show here that PPM1H relies on an N-terminal amphipathic helix for Golgi localization. The amphipathic helix enables PPM1H to bind to liposomes in vitro, and small, highly curved liposomes stimulate PPM1H activity. We artificially anchored PPM1H...

The Parkinson’s VPS35[D620N] mutation causes lysosome dysfunction enhancing LRRK2 kinase activity. We find the VPS35[D620N] mutation alters expression of ∼350 lysosomal proteins and stimulates LRRK2 phosphorylation of Rab proteins at the lysosome. This recruits the phosphoRab effector protein RILPL1 to the lysosome where it binds to the lysosomal i...

Activating mutations in the Leucine Rich Repeat Kinase 2 (LRRK2) cause Parkinson’s disease. LRRK2 phosphorylates a subset of Rab GTPases, particularly Rab10 and Rab8A, and we showed previously that phosphoRabs play an important role in LRRK2 membrane recruitment and activation (Vides et al., 2022). To learn more about LRRK2 pathway regulation, we c...

Activating mutations in the Leucine Rich Repeat Kinase 2 (LRRK2) cause Parkinson's disease and previously we showed that activated LRRK2 phosphorylates a subset of Rab GTPases (Steger et al., 2017). Moreover, Golgi-associated Rab29 can recruit LRRK2 to the surface of the Golgi and activate it there for both auto- and Rab substrate phosphorylation....

Rab GTPases comprise a large family of conserved GTPases that are critical regulators of the secretory and endocytic pathways. The human genome encodes ~65 Rabs that localize to discrete membrane compartments and, when in their GTP‐bound state, bind to effector proteins to carry out diverse functions. Activating mutations in LRRK2 kinase cause Park...

Activating mutations in the Leucine Rich Repeat Kinase 2 (LRRK2) cause Parkinson’s disease and previously we showed that activated LRRK2 phosphorylates a subset of Rab GTPases (Steger et al., 2017). Moreover, Golgi-associated Rab29 can recruit LRRK2 to the surface of the Golgi and activate it there for both auto- and Rab substrate phosphorylation....

Supported lipid bilayers have emerged as an ideal model system to study the interaction of proteins with cellular membranes. We describe here a method to monitor the recruitment of purified LRRK2 kinase onto planar lipid bilayers containing lipid-anchored Rab10 protein using Total Internal Reflection Fluorescence (TIRF) Microscopy.This method utili...

Supported lipid bilayers have emerged as an ideal model system to study the interaction of proteins with cellular membranes. We describe here a method to monitor the recruitment of purified LRRK2 kinase onto planar lipid bilayers containing lipid-anchored Rab10 protein using Total Internal Reflection Fluorescence (TIRF) Microscopy.This method utili...

We report here two genome-wide CRISPR screens performed to identify genes that, when knocked out, alter levels of lysosomal cholesterol or bis(monoacylglycero)phosphate. In addition, these screens were also performed under conditions of NPC1 inhibition to identify modifiers of NPC1 function in lysosomal cholesterol export. The screens confirm tight...

Activating LRRK2 mutations cause Parkinson's disease, and pathogenic LRRK2 kinase interferes with ciliogenesis. Previously, we showed that cholinergic interneurons of the dorsal striatum lose their cilia in R1441C LRRK2 mutant mice (Dhekne et al., 2018). Here, we show that cilia loss is seen as early as 10 weeks of age in these mice and also in two...

Rab29 has been implicated in multiple membrane trafficking processes with no described effectors or regulating proteins. Its fast nucleotide exchange rate and inability to bind GDI in cytosol make it a unique and poorly understood Rab. Because the conventional, “GTP-locked” Rab mutation does not have the desired effect in Rab29, we present here the...

Several labs have shown that Rab29 GTPase can recruit LRRK2 to the surface of the Golgi complex. We describe here a method to monitor direct binding of Rab29 to the LRRK2 N-terminal Armadillo domain using Microscale Thermophoresis. This method utilizes purified, His-tagged LRRK2 Armadillo residues 1-552-labeled with NanoTemper Second Gen NHS-Red 64...

We report here two genome-wide CRISPR screens carried out to identify genes that when knocked out, alter levels of lysosomal cholesterol or bis(monoacylglycero)phosphate. In addition, these screens were also carried out under conditions of NPC1 inhibition to identify modifiers of NPC1 function in lysosomal cholesterol export. The screens confirm ti...

Activating mutations in LRRK2 kinase causes Parkinson’s disease. Pathogenic LRRK2 phosphorylates a subset of Rab GTPases and blocks ciliogenesis. Thus, defining novel phospho-Rab interacting partners is critical to our understanding of the molecular basis of LRRK2 pathogenesis. RILPL2 binds with strong preference to LRRK2-phosphorylated Rab8A and R...

Significance Mutations that activate LRRK2 protein kinase cause Parkinson's disease. LRRK2 phosphorylates a subset of Rab GTPases, in particular Rab8 and Rab10. We show here details related to the mechanism by which Rab10 phosphorylation blocks initiation of cilia formation, fundamental information related to how pathogenic LRRK2 interferes with no...

Previously, we showed that cholinergic interneurons of the dorsal striatum lose cilia in mice harboring the Parkinson's-disease associated, kinase activating, R1441C LRRK2 mutation (Dhekne et al., 2018). Here we show that this phenotype is also seen in two mouse strains carrying the most common human G2019S LRRK2 mutation. Heterozygous loss of the...

We describe here our method for immunostaining of primary cilia in brain sections from wild type and LRRK2 or other mutant mice. Included are procedures for perfusion, tissue harvesting, sectioning and staining, image acquisition and analysis.

Transport of LDL-derived cholesterol from lysosomes into the cytoplasm requires NPC1 protein; NPC1L1 mediates uptake of dietary cholesterol. We introduced single disulfide bonds into NPC1 and NPC1L1 to explore the importance of inter-domain dynamics in cholesterol transport. Using a sensitive method to monitor lysosomal cholesterol efflux, we found...

Transport of LDL-derived cholesterol from lysosomes into the cytoplasm requires NPC1 protein; NPC1L1 mediates uptake of dietary cholesterol. We introduced single disulfide bonds into NPC1 and NPC1L1 to explore the importance of inter-domain dynamics in cholesterol transport. Using a sensitive method to monitor lysosomal cholesterol efflux, we found...

Transport of LDL-derived cholesterol from lysosomes into the cytoplasm requires NPC1 protein; NPC1L1 mediates uptake of dietary cholesterol. We introduced single disulfide bonds into NPC1 and NPC1L1 to explore the importance of inter-domain dynamics in cholesterol transport. Using a sensitive method to monitor lysosomal cholesterol efflux, we found...

Activating mutations in LRRK2 kinase cause Parkinson's disease. Pathogenic LRRK2 phosphorylates a subset of Rab GTPases and blocks ciliogenesis. Thus, defining novel phospho-Rab interacting partners is critical to our understanding of the molecular basis of LRRK2 pathogenesis. RILPL2 binds with strong preference to LRRK2-phosphorylated Rab8A and Ra...

Rab29 has been implicated in multiple membrane trafficking processes with no described effectors or regulating proteins. Its fast nucleotide exchange rate and inability to bind GDI in cytosol make it a unique and poorly understood Rab. Because the conventional, “GTP-locked” Rab mutation does not have the desired effect in Rab29, we present here the...

Mutations that activate LRRK2 protein kinase cause Parkinson’s disease. We have shown previously that Rab10 phosphorylation by LRRK2 enhances its binding to RILPL1 and together, these proteins block cilia formation in a variety of cell types including patient derived iPS cells. We have used live cell fluorescence microscopy to identify, more precis...

Transport of LDL-derived cholesterol from lysosomes into the cytoplasm requires NPC1 protein; NPC1L1 mediates uptake of dietary cholesterol. We introduced single disulfide bonds into NPC1 and NPC1L1 to explore the importance of inter-domain dynamics in cholesterol transport. Using a sensitive method to monitor lysosomal cholesterol efflux, we find...

Mutations that activate LRRK2 protein kinase cause Parkinson's disease. LRRK2 phosphorylates a subset of Rab GTPases within their Switch-II motif controlling interaction with effectors. An siRNA screen of all human protein phosphatases revealed that a poorly studied protein phosphatase, PPM1H, counteracts LRRK2 signaling by specifically dephosphory...

LRRK2 kinase mutations cause familial Parkinson’s disease and increased phosphorylation of a subset of Rab GTPases. Rab29 recruits LRRK2 to the trans-Golgi and activates it there, yet some of LRRK2’s major Rab substrates are not on the Golgi. We sought to characterize the cell biology of LRRK2 activation. Unlike other Rab family members, we show th...

Mutations that activate LRRK2 protein kinase cause Parkinsons disease. LRRK2 phosphorylates a subset of Rab GTPases within their Switch-II motif controlling interaction with effectors. An siRNA screen of all protein phosphatases revealed that a poorly studied protein phosphatase, PPM1H, counteracts LRRK2 signaling by specifically dephosphorylating...

Low-density lipoprotein particles are taken up by cells and delivered to the lysosome where their cholesterol esters are cleaved off by acid lipase. The released, free cholesterol is then exported from lysosomes for cellular needs or storage. This article summarizes recent advances in our understanding of the molecular basis of cholesterol export f...

The authors recently noticed that they had inverted the labeling for the Rab10 and Rab29 blots in Figure 8A. The authors apologize for these errors and any inconvenience caused by this oversight. (Figure presented.).

Extracellular vesicles mediate transfer of biologically active molecules between neighboring or distant cells, and these vesicles may play important roles in normal physiology and the pathogenesis of multiple disease states including cancer. However, the underlying molecular mechanisms of their biogenesis and release remain unknown. We designed art...

Leucine-rich repeat kinase 2 (LRRK2) is mutated in familial Parkinson’s disease, and pathogenic mutations activate the kinase activity. A tour de force screen by Mann and Alessi and co-workers identified a subset of Rab GTPases as bona fide LRRK2 substrates. Rab GTPases are master regulators of membrane trafficking and this short review will summar...

Parkinson's disease-associated LRRK2 kinase phosphorylates multiple Rab GTPases, including Rab8A and Rab10. We show here that LRRK2 kinase interferes with primary cilia formation in cultured cells, human LRRK2 G2019S iPS cells and in the cortex of LRRK2 R1441C mice. Rab10 phosphorylation strengthens its intrinsic ability to block ciliogenesis by en...

Endocytosed, LDL‐derived cholesterol is exported from the interior of lysosomes by a process that requires the action of NPC1 and NPC2 proteins. We have recently shown that LAMP1 and LAMP2 proteins interact with NPC1 and NPC2 and also bind cholesterol (1). LAMPs are highly abundant, ubiquitous, mammalian proteins that line the lysosome limiting mem...

Expanded View Figures PDF

Parkinson's disease predisposing LRRK2 kinase phosphorylates a group of Rab GTPase proteins including Rab29, within the effector-binding switch II motif. Previous work indicated that Rab29, located within the PARK16 locus mutated in Parkinson's patients, operates in a common pathway with LRRK2. Here, we show that Rab29 recruits LRRK2 to the trans-G...

We previously reported that Parkinson's disease (PD) kinase LRRK2 phosphorylates a subset of Rab GTPases on a conserved residue in their switch-II domains (Steger, Tonelli et al., 2016) (PMID: 26824392). Here, we systematically analyzed the Rab protein family and found 14 of them (Rab3A/B/C/D, Rab5A/B/C, Rab8A/B, Rab10, Rab12, Rab29, Rab35 and Rab4...

Summary of used proteases and identified peptides for the proteomic analysis of 52 Rab GTPases. Proteomics raw data have been deposited to the ProteomeXchange Consortium (Vizcaíno et al., 2014) via the PRIDE partner repository with the data set identifier PXD007214.

Several of the most important discoveries in the field of membrane traffic have come from studies of Rab GTPases by Marino Zerial and Peter Novick and their colleagues. Zerial was the first to discover that Rab GTPases represent identity markers for different membrane-bound compartments, and each Rab organizes a collection of specific effectors int...

Methods to quantify intracellular cholesterol are valuable for the study of its trafficking and storage in normal cells and in lysosomal storage disorders. Traditionally, cholesterol has been tracked using the small molecule, filipin. Filipin can be difficult to visualize and visualization can be cytotoxic as it requires UV illumination. Here we de...

LAMP1 and LAMP2 proteins are highly abundant, ubiquitous, mammalian proteins that line the lysosome limiting membrane, and protect it from lysosomal hydrolase action. LAMP2 deficiency causes Danon's disease, an X-linked hypertrophic cardiomyopathy. LAMP2 is needed for chaperone-mediated autophagy, and its expression improves tissue function in mode...

Significance Niemann–Pick C1 (NPC1) and Niemann–Pick C2 (NPC2) cooperate in the export of LDL-derived cholesterol from lysosomes; mutations in these proteins lead to Niemann–Pick type C disease. We present here the crystal structure of an NPC1–NPC2 complex and show that the amino acid residues that are important for this interaction in vitro are al...

An unsolved mystery in cell biology is how unusually large secretory cargoes are exported from the endoplasmic reticulum. In this issue, Santos et al. (2016. J. Cell Biol . http://dx.doi.org/10.1083/jcb.201603072 ) report the function of a Mia2/cTAGE5 transcript fusion, named TALI, in the endoplasmic reticulum export of chylomicrons and very low-de...

Human NPC1L1 protein mediates cholesterol absorption in the intestine and liver, and is the target of the drug Ezetimibe that is used to treat hypercholesterolemia. Previous studies concluded that NPC1L1-GFP protein trafficking is regulated by cholesterol binding, and that Ezetimibe blocks NPC1L1-GFP function by inhibiting its endocytosis. We used...

The Golgi complex is decorated with so-called Golgin proteins that share a common feature: a large proportion of their amino acid sequences are predicted to form coiled-coil structures. The possible presence of extensive coiled coils implies that these proteins are highly elongated molecules that can extend a significant distance from the Golgi sur...

Matlab script for afm image analysis. DOI: http://dx.doi.org/10.7554/eLife.12790.015

Significance Plasma lipoproteins carrying cholesteryl esters are taken up by low density lipoprotein receptors and delivered to lysosomes, where cholesterol is released and then exported for cellular use. Although cholesterol can partition freely between membranes, it does not freely partition out of lysosomes—Niemann-Pick type C 1 (NPC1) protein i...

ELife digest Within our cells there are many compartments that play important roles. Small bubble-like packages called vesicles carry proteins and other molecules between these compartments. These vesicles can be driven around cells by a family of motor proteins called kinesins, which move along a network of filaments called microtubules. Kinesin p...

Mammalian cells encode a diverse set of Rab GTPases and their corresponding regulators. In vitro biochemical screening has proven invaluable in assigning particular Rabs as substrates for their cognate GTPase-activating proteins. However, in vitro activity does not always reflect substrate specificity in cells. This method describes a functional te...

Transport vesicle tethers are proteins that link partner membranes together to permit subsequent SNARE protein pairing and fusion. Despite the identification of a relatively large number of tethering proteins, little is known about the precise mechanisms by which they act. Biochemical isolation of tethers permits direct analysis of their physical c...

Mulitmeric cullin-RING ubiquitin ligases (CRLs) represent the largest class of ubiquitin ligases in eukaryotes. However, most CRL ubiquitylation pathways remain uncharacterized. CRLs control a myriad of functions by catalyzing mono- or poly-ubiquitylation of target proteins. Recently, novel CRLs have been identified along the secretory pathway wher...

The 2013 Nobel Prize in Physiology or Medicine has been awarded to James Rothman, Randy Schekman, and Thomas Südhof "for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells". I present a personal view of the membrane trafficking field, highlighting the contributions of these three Nobel laureates in a hi...

Cyclin E regulates the cell cycle transition from G1 to S phase and is degraded before entry into G2 phase. Here we show that RhoBTB3, a Golgi-associated, Rho-related ATPase, regulates the S/G2 transition of the cell cycle by targeting Cyclin E for ubiquitylation. Depletion of RhoBTB3 arrested cells in S phase, triggered Golgi fragmentation, and el...

Sorting nexin proteins (SNXs) and the cargo-selective retromer complex play key roles in receptor recycling from endosomes to the cell surface. A global proteomics analysis reveals a collection of cell surface proteins that rely on SNX27 and the retromer complex for their cell surface localization at steady state.

Rab GTPases are master regulators of membrane traffic. By binding to distinct sets of effector proteins, Rabs catalyse the formation of function-specifying membrane microdomains. They are delivered to membranes by a protein named GDI (guanine-nucleotide-dissociation inhibitor) and are stabilized there after nucleotide exchange by effector binding....

Rab GTPases are master regulators of membrane trafficking events and template the directionality of protein transport through the secretory and endocytic pathways. Certain Rabs recruit the guanine nucleotide exchange factor (GEF) that activates a subsequent-acting Rab protein in a given pathway; this process has been termed a Rab cascade. We show h...

Rab4A is a master regulator of receptor recycling from endocytic compartments to the plasma membrane. The protein TBC1D16 is up-regulated in melanoma, and TBC1D16-overexpressing melanoma cells are dependent on TBC1D16. We show here that TBC1D16 enhances the intrinsic rate of GTP hydrolysis by Rab4A. TBC1D16 is both cytosolic and membrane associated...

In this issue, Malhotra and colleagues use biochemical approaches to identify a new class of secretory cargo carriers (CARTS) that do not contain the larger cargoes, collagen or Vesicular stomatitis virus (VSV)-G glycoprotein. CARTS appear to be basolateral membrane-directed carriers that use myosin for their motility but not for their formation.

Mutations in the OCRL gene encoding the phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) 5-phosphatase OCRL cause Lowe syndrome (LS), which is characterized by intellectual disability, cataracts and selective proximal tubulopathy. OCRL localizes membrane-bound compartments and is implicated in intracellular transport. Comprehensive analysis of c...

Rab GTPases regulate vesicle budding, motility, docking, and fusion. In cells, their cycling between active, GTP-bound states and inactive, GDP-bound states is regulated by the action of opposing enzymes called guanine nucleotide exchange factors and GTPase-activating proteins (GAPs). The substrates for most RabGAPs are unknown, and the potential f...

Ebola and Marburg filoviruses cause deadly outbreaks of haemorrhagic fever. Despite considerable efforts, no essential cellular receptors for filovirus entry have been identified. We showed previously that Niemann-Pick C1 (NPC1), a lysosomal cholesterol transporter, is required for filovirus entry. Here, we demonstrate that NPC1 is a critical filov...

Rab9 functions in the retrieval of mannose 6-phosphate receptors (MPRs) from late endosomes and their subsequent delivery to the trans Golgi network (TGN). In this chapter, we will discuss how Rab9 is recruited onto membranes, how Rab9 functions to select and segregate MPRs into a specific microdomain depleted of Rab7, and ultimately, how Rab9-cont...

Niemann-Pick type C1 (NPC1) protein is needed for cellular utilization of low-density lipoprotein-derived cholesterol that has been delivered to lysosomes. The protein has 13 transmembrane domains, three large lumenal domains, and a cytoplasmic tail. NPC1's lumenally oriented, N-terminal domain binds cholesterol and has been proposed to receive cho...

GCC185 is a long coiled-coil protein localized to the trans-Golgi network (TGN) that functions in maintaining Golgi structure and tethering mannose 6-phosphate receptor (MPR)-containing transport vesicles en route to the Golgi. We report the identification of two distinct domains of GCC185 needed either for Golgi structure maintenance or transport...

Rab GTPases regulate all steps of membrane trafficking. Their interconversion between active, GTP-bound states and inactive, GDP-bound states is regulated by guanine nucleotide exchange factors and GTPase-activating proteins. The substrates for most Rab GTPase-activating proteins (GAPs) are unknown. Rab9A and its effectors regulate transport of man...

The trans-Golgi network (TGN) receives a select set of proteins from the endocytic pathway-about 5% of total plasma membrane glycoproteins (Duncan and Kornfeld 1988). Proteins that are delivered include mannose 6-phosphate receptors (MPRs), TGN46, sortilin, and various toxins that hitchhike a ride backward through the secretory pathway to intoxicat...

The Golgi complex is a central processing compartment in the secretory pathway of eukaryotic cells. This essential compartment processes more than 30% of the proteins encoded by the human genome, yet we still do not fully understand how the Golgi is assembled and how proteins pass through it. Recent advances in our understanding of the molecular ba...

Membrane trafficking involves the collection of cargo into nascent transport vesicles that bud off from a donor compartment, translocate along cytoskeletal tracks, and then dock and fuse with their target membranes. Docking and fusion involve initial interaction at a distance (tethering), followed by a closer interaction that leads to pairing of ve...

The Golgi complex is a central processing station for proteins traversing the secretory pathway, yet we are still learning how this compartment is constructed and how cargo moves through it. Recent experiments suggest a key role for Ras-like Rab GTPases and provide important new ideas for how the Golgi may function.

In this issue, Duran et al. (2010. J. Cell Biol. doi: 10.1083/jcb.200911154) and Manjithaya et al. (2010. J. Cell Biol. doi: 10.1083/jcb.200911149) use yeast genetics to reveal a role for autophagosome intermediates in the unconventional secretion of an acyl coenzyme A (CoA)-binding protein that lacks an endoplasmic reticulum signal sequence. Mediu...

Exosomes are endosome-derived membrane vesicles that are key for intercellular communication in the immune system and elsewhere. Rab27A and Rab27B GTPases and two of their cognate effector proteins seem to be needed to drive the physiologically important exosome-release process in certain cell types.

The Golgi apparatus is essential for protein sorting and transport. Many researchers have long been fascinated with the form and function of this organelle. Yet, despite decades of scrutiny, the mechanisms by which proteins are transported across the Golgi remain controversial. At a recent meeting, many prominent Golgi researchers assembled to crit...

Proteins use multiple routes for transport from endosomes to the Golgi complex. Shiga and cholera toxins and TGN38/46 are routed from early and recycling endosomes, while mannose 6-phosphate receptors are routed from late endosomes. The identification of distinct molecular requirements for each of these pathways makes it clear that mammalian cells...

Rab proteins are key regulators of membrane traffic (1, 2). The human genome encodes almost 70 Rabs (3); baker's yeast encodes just 11 (4). These small GTPases located on the cytoplasmic surfaces of membrane compartments recruit to those membranes distinct sets of cytosolic proteins (“effectors”). Recruitment ofRab-specific effectors defines a comp...

Rho GTPases are key regulators of the actin-based cytoskeleton; Rab GTPases are key regulators of membrane traffic. We report here that the atypical Rho GTPase family member, RhoBTB3, binds directly to Rab9 GTPase and functions with Rab9 in protein transport from endosomes to the trans Golgi network. Gene replacement experiments show that RhoBTB3 f...

Pfeffer is writing the rulebook for membrane trafficking and protein sorting.

Poly-N-acetyllactosamine (polyLacNAc) is a linear carbohydrate polymer composed of alternating N-acetylglucosamine and galactose residues involved in cellular functions ranging from differentiation to metastasis. PolyLacNAc also serves as a scaffold on which other oligosaccharides such as sialyl Lewis X are displayed. The polymerization of the alte...

GCC185 is a GRIP‐domain containing Golgin that is localized to the trans Golgi network and is required for recycling of mannose 6‐phosphate receptors (MPRs) from endosomes to the Golgi (1). MPRs are present in peripheral, Rab9‐containing vesicles in cells depleted of GCC185; lysosomal hydrolases are also mis‐sorted under these conditions due to the...

Rab GTPases are master regulators of membrane trafficking. Rab GTPase activating proteins (GAPs) enhance a Rab's slow, intrinsic rate of GTP hydrolysis, thereby inactivating them. A so‐called TBC domain is the catalytic domain found in most Rab GAPs. The goal of this study is to determine the functions of RUTBC1 and RUTBC2, which were identified by...