The Many Mechanisms of Viral Membrane Fusion Proteins

Earp, Laurie J.; Delos, Sue E.; Park, H. E.; White, Judith M.

doi:10.1007/3-540-26764-6_2

Cited by 300 publications

(360 citation statements)

References 216 publications

(246 reference statements)

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“…HA-mediated fusion with model or cellular membranes is well documented (reviewed in Ref. 56). Consistent with reported results, we found fusion of HApp to be fast and strictly pH-dependent with a narrow pH optimum around pH 5.0.…”

Section: Discussionsupporting

confidence: 92%

“…This is in striking contrast to what is observed for pH-independent viruses such as some Retroviruses, Paramyxoviruses, Herpesviruses, Coronaviruses, and Poxviruses. Indeed, expression of their fusion capacity relies strictly on receptor-induced conformational changes in their fusion proteins (56). Consistently, we did not observe fusion in our protein-free liposomal system for MLVpp.…”

Section: Discussionsupporting

confidence: 86%

See 1 more Smart Citation

Hepatitis C Virus Glycoproteins Mediate Low pH-dependent Membrane Fusion with Liposomes

Lavillette

Bartosch

Nourrisson

et al. 2006

Journal of Biological Chemistry

126

176

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It has been suggested that the hepatitis C virus (HCV) infects host cells through a pH-dependent internalization mechanism, but the steps leading from virus attachment to the fusion of viral and cellular membranes remain uncharacterized. Here we studied the mechanism underlying the HCV fusion process in vitro using liposomes and our recently described HCV pseudoparticles (pp) bearing functional E1E2 envelope glycoproteins. The fusion of HCVpp with liposomes was monitored with fluorescent probes incorporated into either the HCVpp or the liposomes. To validate these assays, pseudoparticles bearing either the hemagglutinin of the influenza virus or the amphotropic glycoprotein of murine leukemia virus were used as models for pH-dependent and pH-independent entry, respectively. The use of assays based either on fusion-induced dequenching of fluorescent probes or on reporter systems, which produce fluorescence when the virus and liposome contents are mixed, allowed us to demonstrate that HCVpp mediated a complete fusion process, leading to the merging of both membrane leaflets and to the mixing of the internal contents of pseudoparticle and liposome. This HCVpp-mediated fusion was dependent on low pH, with a threshold of 6.3 and an optimum at about 5.5. Fusion was temperature-dependent and did not require any protein or receptor at the surface of the target liposomes. Most interestingly, fusion was facilitated by the presence of cholesterol in the target membrane. These findings clearly indicate that HCV infection is mediated by a pH-dependent membrane fusion process. This paves the way for future studies of the mechanisms underlying HCV membrane fusion. Hepatitis C virus (HCV)2 belongs to the genus Hepacivirus of the Flaviviridae family (1) and has infected some 170 million people worldwide (2). In the majority of HCV-infected patients, the progression to chronic disease is associated with an increased risk of liver diseases and hepatocellular carcinoma. No vaccine is presently available, and the current treatment for chronic hepatitis C (a combination of pegylated interferon and ribavirin) has a limited efficacy (3). A more detailed understanding of the molecular mechanisms of virus entry would be beneficial to the development of novel therapeutic strategies.The HCV genome is a positive-stranded RNA encoding a precursor polyprotein of about 3,000 amino acids. This polyprotein is cleaved coand post-translationally to generate 10 viral proteins, classified into structural (capsid protein and the envelope glycoproteins E1 and E2) and nonstructural proteins (NS2 to NS5B), separated by the membrane ion channel polypeptide p7 (1, 4). The type I transmembrane envelope glycoproteins E1 and E2 form noncovalently linked heterodimers in the endoplasmic reticulum and are highly glycosylated, containing up to 6 and 11 potential glycosylation sites, respectively (5-8). Studies of the HCV life cycle have been hampered by the lack of an efficient and reliable cell culture system to produce and isolate the functional virus. Most re...

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Section: Discussionsupporting

confidence: 92%

Section: Discussionsupporting

confidence: 86%

Hepatitis C Virus Glycoproteins Mediate Low pH-dependent Membrane Fusion with Liposomes

Lavillette

Bartosch

Nourrisson

et al. 2006

Journal of Biological Chemistry

126

176

View full text Add to dashboard Cite

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“…After an initial adhesion step, the fusion proteins link the opposing membranes, followed by protein folding that pulls the membranes in close proximity. Fusion pores form, and the process culminates in the complete merging of the lipid bilayers (Sollner 2004;Earp et al 2005). Viruses use a single protein for both specific contact and for fusion itself, and the several classes of viral fusion proteins apparently evolved independently (Earp et al 2005).…”

Section: Mechanisms Of Gamete Fusionmentioning

confidence: 99%

“…Thus, it remains unknown for any organism whether adhesion of gamete membranes and fusion of the membranes are together accomplished by a single set of proteins, as with fusion of many viruses (Earp et al 2005), or if the two functions are allocated to distinct sets of proteins. We also do not understand the molecular basis for the species specificity of gamete fusion in many organisms (Ferris et al 1997;Swanson and Vacquier 2002;Vieira and Miller 2006).…”

mentioning

confidence: 99%

The conserved plant sterility gene HAP2 functions after attachment of fusogenic membranes in Chlamydomonas and Plasmodium gametes

Liu¹,

Tewari²,

Ning³

et al. 2008

Genes Dev.

307

386

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The cellular and molecular mechanisms that underlie species-specific membrane fusion between male and female gametes remain largely unknown. Here, by use of gene discovery methods in the green alga Chlamydomonas, gene disruption in the rodent malaria parasite Plasmodium berghei, and distinctive features of fertilization in both organisms, we report discovery of a mechanism that accounts for a conserved protein required for gamete fusion. A screen for fusion mutants in Chlamydomonas identified a homolog of HAP2, an Arabidopsis sterility gene. Moreover, HAP2 disruption in Plasmodium blocked fertilization and thereby mosquito transmission of malaria. HAP2 localizes at the fusion site of Chlamydomonas minus gametes, yet Chlamydomonas minus and Plasmodium hap2 male gametes retain the ability, using other, species-limited proteins, to form tight prefusion membrane attachments with their respective gamete partners. Membrane dye experiments show that HAP2 is essential for membrane merger. Thus, in two distantly related eukaryotes, species-limited proteins govern access to a conserved protein essential for membrane fusion.[Keywords: Gamete fusion; cell-cell fusion; malaria; HAP2; Chlamydomonas, Plasmodium] Supplemental material is available at http://www.genesdev.org. Received January 28, 2008; revised version accepted February 22, 2008. Fusion of gametes of opposite sex (or mating type) to form a zygote is the defining moment in the life of a eukaryote. In the first phase of gamete interactions, cell adhesion molecules displayed on the surfaces of the gametes bring the two cells together. In animals, the sperm plasma membrane binds to the extracellular matrix of the egg (the zona pellucida in mammals and the jelly coat in many invertebrates). The interacting gametes use this first-phase adhesion step not only to bind to each other, but also to initiate a signal transduction cascade that activates the sperm and exposes new, fusogenic regions of the sperm plasma membrane. In the second phase of fertilization, the membrane fusion reaction, the plasma membranes of the two gametes come into intimate contact and then fuse, bringing about cytoplasmic continuity (Primakoff and Myles 2002;Rubinstein et al. 2006). Although these two steps-prefusion attachment of the plasma membranes of gametes and merger of their lipid bilayers-have been experimentally separated using in vitro bioassays, gene disruption studies to date have failed to distinguish the two, and no genes have been identified whose disruption allows prefusion attachment and disallows membrane merger. In mice, several proteins involved in gamete membrane interactions have been described, including ADAMS family members and CRISP proteins on sperm and integrins and tetraspanin family members CD9 and CD81 on eggs (for review, see Ellerman et al. 2006;Inoue et al. 2007;Primakoff and Myles 2007). Izumo, an immunoglobulin superfamily sperm protein that appears to be limited to mammals, is gamete-specific and shown by gene disruption to be essential at a late step in ferti...

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“…It was produced by extracting haemagglutinin (HA) and neuraminidase and fatty acids from influenza virus and reassembling them to produce a liposome-like structure (16)(17)(18)(19)(20). The influenza virus enters cells through interaction of the viral envelop glycoprotein HA with sialic acid residues on the target cell surface.…”

Section: Discussionmentioning

confidence: 99%