scholarly journals Regulation of membrane fusion by the membrane-proximal coil of the t-SNARE during zippering of SNAREpins

2002 ◽  
Vol 158 (5) ◽  
pp. 929-940 ◽  
Author(s):  
Thomas J. Melia ◽  
Thomas Weber ◽  
James A. McNew ◽  
Lillian E. Fisher ◽  
Robert J. Johnston ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Fusion Proteins ◽  
The Other ◽  
Proximal Portion ◽  
Intrinsic State ◽  
Temporal Control ◽  
Helical Bundle ◽  
Proximal Half

We utilize structurally targeted peptides to identify a “tC fusion switch” inherent to the coil domains of the neuronal t-SNARE that pairs with the cognate v-SNARE. The tC fusion switch is located in the membrane-proximal portion of the t-SNARE and controls the rate at which the helical bundle that forms the SNAREpin can zip up to drive bilayer fusion. When the fusion switch is “off” (the intrinsic state of the t-SNARE), zippering of the helices from their membrane-distal ends is impeded and fusion is slow. When the tC fusion switch is “on,” fusion is much faster. The tC fusion switch can be thrown by a peptide that corresponds to the membrane-proximal half of the cognate v-SNARE, and binds reversibly to the cognate region of the t-SNARE. This structures the coil in the membrane-proximal domain of the t-SNARE and accelerates fusion, implying that the intrinsically unstable coil in that region is a natural impediment to the completion of zippering, and thus, fusion. Proteins that stabilize or destabilize one or the other state of the tC fusion switch would exert fine temporal control over the rate of fusion after SNAREs have already partly zippered up.

scholarly journals Close Is Not Enough

2000 ◽  
Vol 150 (1) ◽  
pp. 105-118 ◽  
Author(s):  
James A. McNew ◽  
Thomas Weber ◽  
Francesco Parlati ◽  
Robert J. Johnston ◽  
Thomas J. Melia ◽  
...  
Keyword(s):  
Fusion Protein ◽  
Membrane Fusion ◽  
Fusion Proteins ◽  
Active Role ◽  
Snare Complex ◽  
Active Process ◽  
Attachment Protein ◽  
Helical Bundle ◽  
Active Mechanism ◽  
Target Membrane

Is membrane fusion an essentially passive or an active process? It could be that fusion proteins simply need to pin two bilayers together long enough, and the bilayers could do the rest spontaneously. Or, it could be that the fusion proteins play an active role after pinning two bilayers, exerting force in the bilayer in one or another way to direct the fusion process. To distinguish these alternatives, we replaced one or both of the peptidic membrane anchors of exocytic vesicle (v)- and target membrane (t)-SNAREs (soluble N-ethylmaleimide-sensitive fusion protein [NSF] attachment protein [SNAP] receptor) with covalently attached lipids. Replacing either anchor with a phospholipid prevented fusion of liposomes by the isolated SNAREs, but still allowed assembly of trans-SNARE complexes docking vesicles. This result implies an active mechanism; if fusion occurred passively, simply holding the bilayers together long enough would have been sufficient. Studies using polyisoprenoid anchors ranging from 15–55 carbons and multiple phospholipid-containing anchors reveal distinct requirements for anchors of v- and t-SNAREs to function: v-SNAREs require anchors capable of spanning both leaflets, whereas t-SNAREs do not, so long as the anchor is sufficiently hydrophobic. These data, together with previous results showing fusion is inhibited as the length of the linker connecting the helical bundle-containing rod of the SNARE complex to the anchors is increased (McNew, J.A., T. Weber, D.M. Engelman, T.H. Sollner, and J.E. Rothman, 1999. Mol. Cell. 4:415–421), suggests a model in which one activity of the SNARE complex promoting fusion is to exert force on the anchors by pulling on the linkers. This motion would lead to the simultaneous inward movement of lipids from both bilayers, and in the case of the v-SNARE, from both leaflets.

Viral Entry Inhibitors Targeting Six-Helical Bundle Core Against Highly Pathogenic Enveloped Viruses with Class I Fusion Proteins

2021 ◽  
Vol 28 ◽  
Author(s):  
Jing Pu ◽  
Joey Tianyi Zhou ◽  
Ping Liu ◽  
Fei Yu ◽  
Xiaoyang He ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Envelope Protein ◽  
Fusion Proteins ◽  
Viral Envelope ◽  
Class I ◽  
Highly Pathogenic ◽  
Hepatitis D ◽  
Enveloped Viruses ◽  
Helical Bundle ◽  
Entry Inhibitors

: TypeⅠ enveloped viruses bind to cell receptors through surface glycoproteins to initiate infection or undergo receptor-mediated endocytosis. They also initiate membrane fusion in the acidic environment of endocytic compartments, releasing genetic material into the cell. In the process of membrane fusion, envelope protein exposes fusion peptide, followed by insertion into the cell membrane or endosomal membrane. Further conformational changes ensue in which the type 1 envelope protein forms a typical six-helix bundle structure, shortening the distance between viral and cell membranes so that fusion can occur. Entry inhibitors targeting viral envelope proteins, or host factors, are effective antiviral agents and have been widely studied. Some have been used clinically, such as T20 and Maraviroc for human immunodeficiency virus 1 (HIV-1) or Myrcludex B for hepatitis D virus (HDV). This review focuses on entry inhibitors that target the six-helical bundle core against highly pathogenic enveloped viruses with class I fusion proteins, including retroviruses, coronaviruses, influenza A viruses, paramyxoviruses, and filoviruses.

scholarly journals Pancreatic plasma membranes: promiscuous partners in membrane fusion

1994 ◽  
Vol 298 (3) ◽  
pp. 599-604 ◽  
Author(s):  
E G Lee ◽  
S J Marciniak ◽  
C M MacLean ◽  
J M Edwardson
Keyword(s):  
Membrane Fusion ◽  
Plasma Membranes ◽  
Secretory Granules ◽  
The Other ◽  
Zymogen Granules ◽  
Other Hand

We have developed a system in which the fusion of pancreatic plasma membranes with zymogen granules can be studied in vitro. We show here that pancreatic plasma membranes fuse not only with pancreatic zymogen granules but also with parotid secretory granules. In contrast, parotid membranes fuse only with parotid granules and not with pancreatic granules. The extent of fusion is insensitive to Ca2+ for all combinations of plasma membranes and granules. Guanosine 5′-[gamma-thio]triphosphate (GTP[S]), on the other hand, stimulates fusion of pancreatic membranes with both pancreatic granules and parotid granules, but inhibits fusion between parotid membranes and parotid granules.

scholarly journals Interdependent assembly of specific regulatory lipids and membrane fusion proteins into the vertex ring domain of docked vacuoles

2004 ◽  
Vol 167 (6) ◽  
pp. 1087-1098 ◽  
Author(s):  
Rutilio A. Fratti ◽  
Youngsoo Jun ◽  
Alexey J. Merz ◽  
Nathan Margolis ◽  
William Wickner
Keyword(s):  
Membrane Fusion ◽  
Protein Interactions ◽  
Fusion Proteins ◽  
Membrane Microdomains ◽  
Rab Gtpase ◽  
Protein Protein Interactions ◽  
Px Domain ◽  
Protein Partitioning ◽  
Membrane Fusion Proteins ◽  
Rab Effector

Membrane microdomains are assembled by lipid partitioning (e.g., rafts) or by protein–protein interactions (e.g., coated vesicles). During docking, yeast vacuoles assemble “vertex” ring-shaped microdomains around the periphery of their apposed membranes. Vertices are selectively enriched in the Rab GTPase Ypt7p, the homotypic fusion and vacuole protein sorting complex (HOPS)–VpsC Rab effector complex, SNAREs, and actin. Membrane fusion initiates at vertex microdomains. We now find that the “regulatory lipids” ergosterol, diacylglycerol and 3- and 4-phosphoinositides accumulate at vertices in a mutually interdependent manner. Regulatory lipids are also required for the vertex enrichment of SNAREs, Ypt7p, and HOPS. Conversely, SNAREs and actin regulate phosphatidylinositol 3-phosphate vertex enrichment. Though the PX domain of the SNARE Vam7p has direct affinity for only 3-phosphoinositides, all the regulatory lipids which are needed for vertex assembly affect Vam7p association with vacuoles. Thus, the assembly of the vacuole vertex ring microdomain arises from interdependent lipid and protein partitioning and binding rather than either lipid partitioning or protein interactions alone.

PLCζ, a sperm-specific PLC and its potential role in fertilization

2007 ◽  
Vol 74 ◽  
pp. 23-36 ◽  
Author(s):  
Christopher M. Saunders ◽  
Karl Swann ◽  
F. Anthony Lai
Keyword(s):  
Intracellular Calcium ◽  
Membrane Fusion ◽  
Causative Agent ◽  
Calcium Concentration ◽  
Potential Role ◽  
Vital Role ◽  
The Other ◽  
Sperm Protein ◽  
Dramatic Rise ◽  
The Moment

A dramatic rise in intracellular calcium plays a vital role at the moment of fertilization, eliciting the resumption of meiosis and the initiation of embryo development. In mammals, the rise takes the form of oscillations in calcium concentration within the egg, driven by an elevation in inositol trisphosphate. The causative agent of these oscillations is proposed to be a recently described phosphoinositide-specific phospholipase C, PLCζ, a soluble sperm protein that is delivered into the egg following membrane fusion. In the present review, we examine some of the distinctive structural and functional characteristics of this crucial enzyme that sets it apart from the other known forms of mammalian PLC.

scholarly journals Membrane Fusion Proteins Are Required for oskar mRNA Localization in the Drosophila Egg Chamber

2000 ◽  
Vol 218 (2) ◽  
pp. 314-325 ◽  
Author(s):  
Douglas M Ruden ◽  
Vincent Sollars ◽  
Xiaoyan Wang ◽  
Daisuke Mori ◽  
Marina Alterman ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Fusion Proteins ◽  
Mrna Localization ◽  
Egg Chamber ◽  
Membrane Fusion Proteins

scholarly journals Functional Relevance of the Transmembrane Domain and Cytoplasmic Tail of the Pseudorabies Virus Glycoprotein H for Membrane Fusion

2018 ◽  
Vol 92 (12) ◽  
Author(s):  
Melina Vallbracht ◽  
Walter Fuchs ◽  
Barbara G. Klupp ◽  
Thomas C. Mettenleiter
Keyword(s):  
Membrane Fusion ◽  
Fusion Proteins ◽  
Essential Role ◽  
Pseudorabies Virus ◽  
Transmembrane Domain ◽  
Cytoplasmic Tail ◽  
Class Iii ◽  
Complex Needs ◽  
Hsv 1

ABSTRACTHerpesvirus membrane fusion depends on the core fusion machinery, comprised of glycoproteins B (gB) and gH/gL. Although gB structurally resembles autonomous class III fusion proteins, it strictly depends on gH/gL to drive membrane fusion. Whether the gH/gL complex needs to be membrane anchored to fulfill its function and which role the gH cytoplasmic (CD) and transmembrane domains (TMD) play in fusion is unclear. While the gH CD and TMD play an important role during infection, soluble gH/gL of herpes simplex virus 1 (HSV-1) seems to be sufficient to mediate cell-cell fusion in transient assays, arguing against an essential contribution of the CD and TMD. To shed more light on this apparent discrepancy, we investigated the role of the CD and TMD of the related alphaherpesvirus pseudorabies virus (PrV) gH. For this purpose, we expressed C-terminally truncated and soluble gH and replaced the TMD with a glycosylphosphatidylinositol (gpi) anchor. We also generated chimeras containing the TMD and/or CD of PrV gD or HSV-1 gH. Proteins were characterized in cell-based fusion assays and during virus infection. Although truncation of the CD resulted in decreased membrane fusion activity, the mutant proteins still supported replication of gH-negative PrV, indicating that the PrV gH CD is dispensable for viral replication. In contrast, PrV gH lacking the TMD, membrane-anchored via a lipid linker, or comprising the PrV gD TMD were nonfunctional, highlighting the essential role of the gH TMD for function. Interestingly, despite low sequence identity, the HSV-1 gH TMD could substitute for the PrV gH TMD, pointing to functional conservation.IMPORTANCEEnveloped viruses depend on membrane fusion for virus entry. While this process can be mediated by only one or two proteins, herpesviruses depend on the concerted action of at least three different glycoproteins. Although gB has features of bona fide fusion proteins, it depends on gH and its complex partner, gL, for fusion. Whether gH/gL prevents premature fusion or actively triggers gB-mediated fusion is unclear, and there are contradictory results on whether gH/gL function requires stable membrane anchorage or whether the ectodomains alone are sufficient. Our results show that in pseudorabies virus gH, the transmembrane anchor plays an essential role for gB-mediated fusion while the cytoplasmic tail is not strictly required.

scholarly journals Differential Cholesterol Binding by Class II Fusion Proteins Determines Membrane Fusion Properties

2008 ◽  
Vol 82 (18) ◽  
pp. 9245-9253 ◽  
Author(s):  
M. Umashankar ◽  
Claudia Sánchez-San Martín ◽  
Maofu Liao ◽  
Brigid Reilly ◽  
Alice Guo ◽  
...  
Keyword(s):  
Fusion Protein ◽  
Membrane Fusion ◽  
Fusion Proteins ◽  
Sindbis Virus ◽  
Semliki Forest Virus ◽  
Yellow Fever Virus ◽  
Class Ii ◽  
Binding Properties ◽  
Functional Differences ◽  
Cholesterol Binding

ABSTRACT The class II fusion proteins of the alphaviruses and flaviviruses mediate virus infection by driving the fusion of the virus membrane with that of the cell. These fusion proteins are triggered by low pH, and their structures are strikingly similar in both the prefusion dimer and the postfusion homotrimer conformations. Here we have compared cholesterol interactions during membrane fusion by these two groups of viruses. Using cholesterol-depleted insect cells, we showed that fusion and infection by the alphaviruses Semliki Forest virus (SFV) and Sindbis virus were strongly promoted by cholesterol, with similar sterol dependence in laboratory and field isolates and in viruses passaged in tissue culture. The E1 fusion protein from SFV bound cholesterol, as detected by labeling with photocholesterol and by cholesterol extraction studies. In contrast, fusion and infection by numerous strains of the flavivirus dengue virus (DV) and by yellow fever virus 17D were cholesterol independent, and the DV fusion protein did not show significant cholesterol binding. SFV E1 is the first virus fusion protein demonstrated to directly bind cholesterol. Taken together, our results reveal important functional differences conferred by the cholesterol-binding properties of class II fusion proteins.

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