Arfs and membrane lipids: sensing, generating and responding to membrane curvature

2008 ◽  
Vol 414 (2) ◽  
pp. e1-e2 ◽  
Author(s):  
Julie G. Donaldson
Keyword(s):  
Membrane Trafficking ◽  
Membrane Lipids ◽  
Membrane Curvature ◽  
Coat Proteins ◽  
Membrane Interaction ◽  
Protein Activation ◽  
Membrane Surfaces ◽  
Transport Vesicles ◽  
Biochemical Journal ◽  
Α Helix

Arf family GTP-binding proteins function in the regulation of membrane-trafficking events and in the maintenance of organelle structure. They act at membrane surfaces to modify lipid composition and to recruit coat proteins for the generation of transport vesicles. Arfs associate with membranes through insertion of an N-terminal myristoyl moiety in conjunction with an adjacent amphipathic α-helix, which embeds in the lipid bilayer when Arf1 is GTP-bound. In this issue of the Biochemical Journal, Lundmark et al. report that myristoylated Arfs in the presence of GTP bind to and cause tubulation of liposomes, and that GTP exchange on to Arfs is more efficient in the presence of liposomes of smaller diameter (increased curvature). These findings suggest that Arf protein activation and membrane interaction may initiate membrane curvature that will be enhanced further by coat proteins during vesicle formation.

Arfs, phosphoinositides and membrane traffic

2005 ◽  
Vol 33 (6) ◽  
pp. 1276-1278 ◽  
Author(s):  
J.G. Donaldson
Keyword(s):  
Golgi Complex ◽  
Membrane Trafficking ◽  
Membrane Lipids ◽  
Membrane Traffic ◽  
Type I ◽  
Coat Proteins ◽  
Endosomal Membrane ◽  
Membrane Surfaces ◽  
Phosphatidylinositol 4 ◽  
Cytoskeletal Elements

Arf (ADP-ribosylation factor) GTP-binding proteins function in cells to regulate membrane traffic and structure. Arfs accomplish this task through modification of membrane lipids and the recruitment of proteins, including coat proteins and actin, to membrane surfaces. Arf1 and Arf6 are the most divergent and most studied human Arf proteins that localize predominantly to the Golgi complex and plasma membrane respectively. We have been studying the targeting of Arf1 and Arf6 to these specific compartments and the common and divergent activities that they exert on these membranes. We have found that Arf6 acts through activation of type I phosphatidylinositol 4-phosphate 5-kinases to generate phosphatidylinositol 4,5-bisphosphate and that this activity is instrumental in facilitating the actin cytoskeletal rearrangements and alterations in endosomal membrane trafficking observed with increased Arf6 activation. Arf1 can also stimulate the activity of phosphatidylinositol kinases and recruit coat proteins and actin cytoskeletal elements to the Golgi complex.

Viral Fusion Peptides: A Tool Set to Disrupt and Connect Biological Membranes

2000 ◽  
Vol 20 (6) ◽  
pp. 501-518 ◽  
Author(s):  
Lukas K. Tamm ◽  
Xing Han
Keyword(s):  
Lipid Bilayers ◽  
Biological Membrane ◽  
Membrane Curvature ◽  
Current Evidence ◽  
Viral Fusion ◽  
Fusion Peptides ◽  
Membrane Surfaces ◽  
Self Association ◽  
Α Helix ◽  
And Function

The structure and function of viral fusion peptides are reviewed. The fusion peptides of influenza virus hemagglutinin and human immunodeficiency virus are used as paradigms. Fusion peptides associated with lipid bilayers are conformationally polymorphic. Current evidence suggests that the fusion-promoting state is the obliquely inserted α-helix. Fusion peptides also have a tendency to self-associate into γ-sheets at membrane surfaces. Although the conformational conversion between α- and γ-states is reversible under controlled conditions, its physiological relevance is not yet known. The energetics of peptide insertion and self-association could be measured recently using more soluble “second generation” fusion peptides. Fusion peptides have been reported to change membrane curvature and the state of hydration of membrane surfaces. The combined results are built into a model for the mechanism by which fusion peptides are proposed to assist in biological membrane fusion.

Membrane curvature and the control of GTP hydrolysis in Arf1 during COPI vesicle formation

2005 ◽  
Vol 33 (4) ◽  
pp. 619-622 ◽  
Author(s):  
B. Antonny ◽  
J. Bigay ◽  
J.-F. Casella ◽  
G. Drin ◽  
B. Mesmin ◽  
...  
Keyword(s):  
Lipid Membranes ◽  
Membrane Curvature ◽  
Gtp Hydrolysis ◽  
Membrane Fission ◽  
Transport Vesicles ◽  
Highly Sensitive ◽  
Copi Vesicle ◽  
Membrane Budding ◽  
Gtpase Cycle ◽  
Adp Ribosylation Factor

The GTP switch of the small G-protein Arf1 (ADP-ribosylation factor 1) on lipid membranes promotes the polymerization of the COPI (coat protein complex I) coat, which acts as a membrane deforming shell to form transport vesicles. Real-time measurements for coat assembly on liposomes gives insights into how the GTPase cycle of Arf1 is coupled in time with the polymerization of the COPI coat and the resulting membrane deformation. One key parameter seems to be the membrane curvature. Arf-GAP1 (where GAP stands for GTPase-activating protein), which promotes GTP hydrolysis in the Arf1–COPI complex is highly sensitive to lipid packing. Its activity on Arf1-GTP increases by two orders of magnitude as the diameter of the liposomes approaches that of authentic transport vesicles (60 nm). This suggests that during membrane budding, Arf1-GTP molecules are progressively eliminated from the coated area where the membrane curvature is positive, but are protected from Arf-GAP1 at the bud neck due to the negative curvature of this region. As a result, the coat should be stable as long as the bud remains attached and should disassemble as soon as membrane fission occurs.

scholarly journals Proteomic analysis of monolayer-integrated proteins on lipid droplets identifies amphipathic interfacial α-helical membrane anchors

2018 ◽  
Vol 115 (35) ◽  
pp. E8172-E8180 ◽  
Author(s):  
Camille I. Pataki ◽  
João Rodrigues ◽  
Lichao Zhang ◽  
Junyang Qian ◽  
Bradley Efron ◽  
...  
Keyword(s):  
Lipid Droplets ◽  
Coarse Grained ◽  
Structural Basis ◽  
Endoplasmic Reticulum Membrane ◽  
Membrane Surfaces ◽  
Common Motif ◽  
Cysteine Scanning Mutagenesis ◽  
Α Helix ◽  
Dynamics Simulations ◽  
Integral Proteins

Despite not spanning phospholipid bilayers, monotopic integral proteins (MIPs) play critical roles in organizing biochemical reactions on membrane surfaces. Defining the structural basis by which these proteins are anchored to membranes has been hampered by the paucity of unambiguously identified MIPs and a lack of computational tools that accurately distinguish monolayer-integrating motifs from bilayer-spanning transmembrane domains (TMDs). We used quantitative proteomics and statistical modeling to identify 87 high-confidence candidate MIPs in lipid droplets, including 21 proteins with predicted TMDs that cannot be accommodated in these monolayer-enveloped organelles. Systematic cysteine-scanning mutagenesis showed the predicted TMD of one candidate MIP, DHRS3, to be a partially buried amphipathic α-helix in both lipid droplet monolayers and the cytoplasmic leaflet of endoplasmic reticulum membrane bilayers. Coarse-grained molecular dynamics simulations support these observations, suggesting that this helix is most stable at the solvent–membrane interface. The simulations also predicted similar interfacial amphipathic helices when applied to seven additional MIPs from our dataset. Our findings suggest that interfacial helices may be a common motif by which MIPs are integrated into membranes, and provide high-throughput methods to identify and study MIPs.

Coat Proteins and Selective Protein Packaging into Transport Vesicles

1995 ◽  
Vol 60 (0) ◽  
pp. 11-21 ◽  
Author(s):  
R. Schekman ◽  
C. Barlowe ◽  
S. Bernarek ◽  
J. Campbell ◽  
T. Doering ◽  
...  
Keyword(s):  
Coat Proteins ◽  
Transport Vesicles

scholarly journals SEC16A is a RAB10 effector required for insulin-stimulated GLUT4 trafficking in adipocytes

2016 ◽  
Vol 214 (1) ◽  
pp. 61-76 ◽  
Author(s):  
Joanne Bruno ◽  
Alexandria Brumfield ◽  
Natasha Chaudhary ◽  
David Iaea ◽  
Timothy E. McGraw
Keyword(s):  
Glucose Transporter ◽  
Whole Body ◽  
Site Formation ◽  
Coated Vesicle ◽  
Coat Proteins ◽  
Insulin Stimulation ◽  
Exit Site ◽  
Recycling Endosome ◽  
Transport Vesicles ◽  
Intracellular Compartments

RAB10 is a regulator of insulin-stimulated translocation of the GLUT4 glucose transporter to the plasma membrane (PM) of adipocytes, which is essential for whole-body glucose homeostasis. We establish SEC16A as a novel RAB10 effector in this process. Colocalization of SEC16A with RAB10 is augmented by insulin stimulation, and SEC16A knockdown attenuates insulin-induced GLUT4 translocation, phenocopying RAB10 knockdown. We show that SEC16A and RAB10 promote insulin-stimulated mobilization of GLUT4 from a perinuclear recycling endosome/TGN compartment. We propose RAB10–SEC16A functions to accelerate formation of the vesicles that ferry GLUT4 to the PM during insulin stimulation. Because GLUT4 continually cycles between the PM and intracellular compartments, the maintenance of elevated cell-surface GLUT4 in the presence of insulin requires accelerated biogenesis of the specialized GLUT4 transport vesicles. The function of SEC16A in GLUT4 trafficking is independent of its previously characterized activity in ER exit site formation and therefore independent of canonical COPII-coated vesicle function. However, our data support a role for SEC23A, but not the other COPII components SEC13, SEC23B, and SEC31, in the insulin stimulation of GLUT4 trafficking, suggesting that vesicles derived from subcomplexes of COPII coat proteins have a role in the specialized trafficking of GLUT4.

scholarly journals The Membrane Protein Alkaline Phosphatase Is Delivered to the Vacuole by a Route That Is Distinct from the VPS-dependent Pathway

1997 ◽  
Vol 138 (3) ◽  
pp. 531-545 ◽  
Author(s):  
Robert C. Piper ◽  
Nia J. Bryant ◽  
Tom H. Stevens
Keyword(s):  
Alkaline Phosphatase ◽  
Membrane Protein ◽  
Membrane Trafficking ◽  
Transmembrane Domain ◽  
Alternative Pathway ◽  
Loss Of Function ◽  
Yeast Saccharomyces Cerevisiae ◽  
Atpase Subunit ◽  
Transport Vesicles ◽  
Dependent Pathway

Membrane trafficking intermediates involved in the transport of proteins between the TGN and the lysosome-like vacuole in the yeast Saccharomyces cerevisiae can be accumulated in various vps mutants. Loss of function of Vps45p, an Sec1p-like protein required for the fusion of Golgi-derived transport vesicles with the prevacuolar/endosomal compartment (PVC), results in an accumulation of post-Golgi transport vesicles. Similarly, loss of VPS27 function results in an accumulation of the PVC since this gene is required for traffic out of this compartment. The vacuolar ATPase subunit Vph1p transits to the vacuole in the Golgi-derived transport vesicles, as defined by mutations in VPS45, and through the PVC, as defined by mutations in VPS27. In this study we demonstrate that, whereas VPS45 and VPS27 are required for the vacuolar delivery of several membrane proteins, the vacuolar membrane protein alkaline phosphatase (ALP) reaches its final destination without the function of these two genes. Using a series of ALP derivatives, we find that the information to specify the entry of ALP into this alternative pathway to the vacuole is contained within its cytosolic tail, in the 13 residues adjacent to the transmembrane domain, and loss of this sorting determinant results in a protein that follows the VPS-dependent pathway to the vacuole. Using a combination of immunofluorescence localization and pulse/chase immunoprecipitation analysis, we demonstrate that, in addition to ALP, the vacuolar syntaxin Vam3p also follows this VPS45/27-independent pathway to the vacuole. In addition, the function of Vam3p is required for membrane traffic along the VPS-independent pathway.

scholarly journals Autophagy in the context of the cellular membrane-trafficking system: the enigma of Atg9 vesicles

2017 ◽  
Vol 45 (6) ◽  
pp. 1323-1331 ◽  
Author(s):  
Takeshi Noda
Keyword(s):  
Membrane Protein ◽  
Membrane Trafficking ◽  
De Novo ◽  
Membrane Lipids ◽  
Cellular Membrane ◽  
Current Understanding ◽  
Membrane Structures ◽  
Autophagosome Formation ◽  
Intracellular Degradation

Macroautophagy is an intracellular degradation system that involves the de novo formation of membrane structures called autophagosomes, although the detailed process by which membrane lipids are supplied during autophagosome formation is yet to be elucidated. Macroautophagy is thought to be associated with canonical membrane trafficking, but several mechanistic details are still missing. In this review, the current understanding and potential mechanisms by which membrane trafficking participates in macroautophagy are described, with a focus on the enigma of the membrane protein Atg9, for which the proximal mechanisms determining its movement are disputable, despite its key role in autophagosome formation.

scholarly journals Oligomerization and Ca2+/calmodulin control binding of the ER Ca2+-sensors STIM1 and STIM2 to plasma membrane lipids

2013 ◽  
Vol 33 (5) ◽  
Author(s):  
Rajesh Bhardwaj ◽  
Hans-Michael Müller ◽  
Walter Nickel ◽  
Matthias Seedorf
Keyword(s):  
Plasma Membrane ◽  
Membrane Lipids ◽  
Lipid Binding ◽  
Dependent Manner ◽  
Activation Threshold ◽  
Concentration Dependent Manner ◽  
Rich Domain ◽  
Α Helix ◽  
Distinct Features ◽  
Ca2 Channels

Ca2+ (calcium) homoeostasis and signalling rely on physical contacts between Ca2+ sensors in the ER (endoplasmic reticulum) and Ca2+ channels in the PM (plasma membrane). STIM1 (stromal interaction molecule 1) and STIM2 Ca2+ sensors oligomerize upon Ca2+ depletion in the ER lumen, contact phosphoinositides at the PM via their cytosolic lysine (K)-rich domains, and activate Ca2+ channels. Differential sensitivities of STIM1 and STIM2 towards ER luminal Ca2+ have been studied but responses towards elevated cytosolic Ca2+ concentration and the mechanism of lipid binding remain unclear. We found that tetramerization of the STIM1 K-rich domain is necessary for efficient binding to PI(4,5)P2-containing PM-like liposomes consistent with an oligomerization-driven STIM1 activation. In contrast, dimerization of STIM2 K-rich domain was sufficient for lipid binding. Furthermore, the K-rich domain of STIM2, but not of STIM1, forms an amphipathic α-helix. These distinct features of the STIM2 K-rich domain cause an increased affinity for PI(4,5)P2, consistent with the lower activation threshold of STIM2 and a function as regulator of basal Ca2+ levels. Concomitant with higher affinity for PM lipids, binding of CaM (calmodulin) inhibited the interaction of the STIM2 K-rich domain with liposomes in a Ca2+ and PI(4,5)P2 concentration-dependent manner. Therefore we suggest that elevated cytosolic Ca2+ concentration down-regulates STIM2-mediated ER–PM contacts via CaM binding.

scholarly journals Golgi Structure Correlates with Transitional Endoplasmic Reticulum Organization in Pichia pastoris and Saccharomyces cerevisiae

1999 ◽  
Vol 145 (1) ◽  
pp. 69-81 ◽  
Author(s):  
Olivia W. Rossanese ◽  
Jon Soderholm ◽  
Brooke J. Bevis ◽  
Irina B. Sears ◽  
James O'Connor ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Pichia Pastoris ◽  
Fluorescent Protein ◽  
Molecular Genetic ◽  
Molecular Genetic Analysis ◽  
Coat Proteins ◽  
Transport Vesicles ◽  
Copii Vesicle ◽  
Copii Vesicles ◽  
Green Fluorescent

Golgi stacks are often located near sites of “transitional ER” (tER), where COPII transport vesicles are produced. This juxtaposition may indicate that Golgi cisternae form at tER sites. To explore this idea, we examined two budding yeasts: Pichia pastoris, which has coherent Golgi stacks, and Saccharomyces cerevisiae, which has a dispersed Golgi. tER structures in the two yeasts were visualized using fusions between green fluorescent protein and COPII coat proteins. We also determined the localization of Sec12p, an ER membrane protein that initiates the COPII vesicle assembly pathway. In P. pastoris, Golgi stacks are adjacent to discrete tER sites that contain COPII coat proteins as well as Sec12p. This arrangement of the tER-Golgi system is independent of microtubules. In S. cerevisiae, COPII vesicles appear to be present throughout the cytoplasm and Sec12p is distributed throughout the ER, indicating that COPII vesicles bud from the entire ER network. We propose that P. pastoris has discrete tER sites and therefore generates coherent Golgi stacks, whereas S. cerevisiae has a delocalized tER and therefore generates a dispersed Golgi. These findings open the way for a molecular genetic analysis of tER sites.

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