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J Virol. Dec 1992; 66(12): 7309–7318.
PMCID: PMC240435

Membrane fusion of Semliki Forest virus involves homotrimers of the fusion protein.


Infection of cells with enveloped viruses is accomplished through membrane fusion. The binding and fusion processes are mediated by the spike proteins in the envelope of the virus particle and usually involve a series of conformational changes in these proteins. We have studied the low-pH-mediated fusion process of the alphavirus Semliki Forest virus (SFV). The spike protein of SFV is composed of three copies of the protein heterodimer E2E1. This structure is resistant to solubilization in mild detergents such as Nonidet P-40 (NP40). We have recently shown that the spike structure is reorganized during virus entry into acidic endosomes (J. M. Wahlberg and H. Garoff, J. Cell Biol. 116:339-348, 1992). The original NP40-resistant heterodimer is dissociated, and the E1 subunits form new NP40-resistant protein oligomers. Here, we show that the new oligomer is represented by an E1 trimer. From studies that use an in vitro assay for fusion of SFV with liposomes, we show that the E1 trimer is efficiently expressed during virus-mediated membrane fusion. Time course studies show that both E1 trimer formation and fusion are fast processes, occurring in seconds. It was also possible to inhibit virus binding and fusion with a monoclonal antibody directed toward the trimeric E1. These results give support for a model in which the E1 trimeric structure is involved in the SFV-mediated fusion reaction.

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Selected References

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  • Allan JS. Receptor-mediated activation of immunodeficiency viruses in viral fusion. Science. 1991 May 31;252(5010):1322–1323. [PubMed]
  • Anthony RP, Brown DT. Protein-protein interactions in an alphavirus membrane. J Virol. 1991 Mar;65(3):1187–1194. [PMC free article] [PubMed]
  • BLIGH EG, DYER WJ. A rapid method of total lipid extraction and purification. Can J Biochem Physiol. 1959 Aug;37(8):911–917. [PubMed]
  • Boere WA, Harmsen T, Vinjé J, Benaissa-Trouw BJ, Kraaijeveld CA, Snippe H. Identification of distinct antigenic determinants on Semliki Forest virus by using monoclonal antibodies with different antiviral activities. J Virol. 1984 Nov;52(2):575–582. [PMC free article] [PubMed]
  • Cutler DF, Garoff H. Mutants of the membrane-binding region of Semliki Forest virus E2 protein. I. Cell surface transport and fusogenic activity. J Cell Biol. 1986 Mar;102(3):889–901. [PMC free article] [PubMed]
  • de Curtis I, Simons K. Dissection of Semliki Forest virus glycoprotein delivery from the trans-Golgi network to the cell surface in permeabilized BHK cells. Proc Natl Acad Sci U S A. 1988 Nov;85(21):8052–8056. [PMC free article] [PubMed]
  • Doms RW, Helenius A. Quaternary structure of influenza virus hemagglutinin after acid treatment. J Virol. 1986 Dec;60(3):833–839. [PMC free article] [PubMed]
  • Flynn DC, Meyer WJ, Mackenzie JM, Jr, Johnston RE. A conformational change in Sindbis virus glycoproteins E1 and E2 is detected at the plasma membrane as a consequence of early virus-cell interaction. J Virol. 1990 Aug;64(8):3643–3653. [PMC free article] [PubMed]
  • Fuller SD. The T=4 envelope of Sindbis virus is organized by interactions with a complementary T=3 capsid. Cell. 1987 Mar 27;48(6):923–934. [PubMed]
  • Galla HJ, Hartmann W. Excimer-forming lipids in membrane research. Chem Phys Lipids. 1980 Oct;27(3):199–219. [PubMed]
  • Garoff H, Simons K. Location of the spike glycoproteins in the Semliki Forest virus membrane. Proc Natl Acad Sci U S A. 1974 Oct;71(10):3988–3992. [PMC free article] [PubMed]
  • Godley L, Pfeifer J, Steinhauer D, Ely B, Shaw G, Kaufmann R, Suchanek E, Pabo C, Skehel JJ, Wiley DC, et al. Introduction of intersubunit disulfide bonds in the membrane-distal region of the influenza hemagglutinin abolishes membrane fusion activity. Cell. 1992 Feb 21;68(4):635–645. [PubMed]
  • Helenius A, Fries E, Garoff H, Simons K. Solubilization of the Semliki Forest virus membrane with sodium deoxycholate. Biochim Biophys Acta. 1976 Jun 17;436(2):319–334. [PubMed]
  • Hoekstra D, Kok JW. Entry mechanisms of enveloped viruses. Implications for fusion of intracellular membranes. Biosci Rep. 1989 Jun;9(3):273–305. [PubMed]
  • Kielian M, Helenius A. pH-induced alterations in the fusogenic spike protein of Semliki Forest virus. J Cell Biol. 1985 Dec;101(6):2284–2291. [PMC free article] [PubMed]
  • Kielian M, Jungerwirth S, Sayad KU, DeCandido S. Biosynthesis, maturation, and acid activation of the Semliki Forest virus fusion protein. J Virol. 1990 Oct;64(10):4614–4624. [PMC free article] [PubMed]
  • Kielian MC, Helenius A. Role of cholesterol in fusion of Semliki Forest virus with membranes. J Virol. 1984 Oct;52(1):281–283. [PMC free article] [PubMed]
  • Klenk HD, Rott R, Orlich M, Blödorn J. Activation of influenza A viruses by trypsin treatment. Virology. 1975 Dec;68(2):426–439. [PubMed]
  • Liljeström P, Garoff H. A new generation of animal cell expression vectors based on the Semliki Forest virus replicon. Biotechnology (N Y) 1991 Dec;9(12):1356–1361. [PubMed]
  • Liljeström P, Lusa S, Huylebroeck D, Garoff H. In vitro mutagenesis of a full-length cDNA clone of Semliki Forest virus: the small 6,000-molecular-weight membrane protein modulates virus release. J Virol. 1991 Aug;65(8):4107–4113. [PMC free article] [PubMed]
  • Lobigs M, Garoff H. Fusion function of the Semliki Forest virus spike is activated by proteolytic cleavage of the envelope glycoprotein precursor p62. J Virol. 1990 Mar;64(3):1233–1240. [PMC free article] [PubMed]
  • Lobigs M, Wahlberg JM, Garoff H. Spike protein oligomerization control of Semliki Forest virus fusion. J Virol. 1990 Oct;64(10):5214–5218. [PMC free article] [PubMed]
  • Marsh M, Helenius A. Virus entry into animal cells. Adv Virus Res. 1989;36:107–151. [PubMed]
  • Metsikkö K, Garoff H. Oligomers of the cytoplasmic domain of the p62/E2 membrane protein of Semliki Forest virus bind to the nucleocapsid in vitro. J Virol. 1990 Oct;64(10):4678–4683. [PMC free article] [PubMed]
  • Moore JP, McKeating JA, Weiss RA, Sattentau QJ. Dissociation of gp120 from HIV-1 virions induced by soluble CD4. Science. 1990 Nov 23;250(4984):1139–1142. [PubMed]
  • Omar A, Koblet H. Semliki Forest virus particles containing only the E1 envelope glycoprotein are infectious and can induce cell-cell fusion. Virology. 1988 Sep;166(1):17–23. [PubMed]
  • Pal R, Barenholz Y, Wagner RR. Pyrene phospholipid as a biological fluorescent probe for studying fusion of virus membrane with liposomes. Biochemistry. 1988 Jan 12;27(1):30–36. [PubMed]
  • Peterson GL. A simplification of the protein assay method of Lowry et al. which is more generally applicable. Anal Biochem. 1977 Dec;83(2):346–356. [PubMed]
  • Phalen T, Kielian M. Cholesterol is required for infection by Semliki Forest virus. J Cell Biol. 1991 Feb;112(4):615–623. [PMC free article] [PubMed]
  • Rafalski M, Ortiz A, Rockwell A, van Ginkel LC, Lear JD, DeGrado WF, Wilschut J. Membrane fusion activity of the influenza virus hemagglutinin: interaction of HA2 N-terminal peptides with phospholipid vesicles. Biochemistry. 1991 Oct 22;30(42):10211–10220. [PubMed]
  • Salminen A, Wahlberg JM, Lobigs M, Liljeström P, Garoff H. Membrane fusion process of Semliki Forest virus. II: Cleavage-dependent reorganization of the spike protein complex controls virus entry. J Cell Biol. 1992 Jan;116(2):349–357. [PMC free article] [PubMed]
  • Simons K, Helenius A, Garoff H. Solubilization of the membrane proteins from Semliki Forest virus with Triton X100. J Mol Biol. 1973 Oct 15;80(1):119–133. [PubMed]
  • Stegmann T, Booy FP, Wilschut J. Effects of low pH on influenza virus. Activation and inactivation of the membrane fusion capacity of the hemagglutinin. J Biol Chem. 1987 Dec 25;262(36):17744–17749. [PubMed]
  • Stegmann T, Delfino JM, Richards FM, Helenius A. The HA2 subunit of influenza hemagglutinin inserts into the target membrane prior to fusion. J Biol Chem. 1991 Sep 25;266(27):18404–18410. [PubMed]
  • Stegmann T, Doms RW, Helenius A. Protein-mediated membrane fusion. Annu Rev Biophys Biophys Chem. 1989;18:187–211. [PubMed]
  • Stegmann T, Hoekstra D, Scherphof G, Wilschut J. Fusion activity of influenza virus. A comparison between biological and artificial target membrane vesicles. J Biol Chem. 1986 Aug 25;261(24):10966–10969. [PubMed]
  • Stegmann T, White JM, Helenius A. Intermediates in influenza induced membrane fusion. EMBO J. 1990 Dec;9(13):4231–4241. [PMC free article] [PubMed]
  • Struck DK, Hoekstra D, Pagano RE. Use of resonance energy transfer to monitor membrane fusion. Biochemistry. 1981 Jul 7;20(14):4093–4099. [PubMed]
  • van Meer G, Davoust J, Simons K. Parameters affecting low-pH-mediated fusion of liposomes with the plasma membrane of cells infected with influenza virus. Biochemistry. 1985 Jul 2;24(14):3593–3602. [PubMed]
  • Vogel RH, Provencher SW, von Bonsdorff CH, Adrian M, Dubochet J. Envelope structure of Semliki Forest virus reconstructed from cryo-electron micrographs. Nature. 1986 Apr 10;320(6062):533–535. [PubMed]
  • Wahlberg JM, Boere WA, Garoff H. The heterodimeric association between the membrane proteins of Semliki Forest virus changes its sensitivity to low pH during virus maturation. J Virol. 1989 Dec;63(12):4991–4997. [PMC free article] [PubMed]
  • Wahlberg JM, Garoff H. Membrane fusion process of Semliki Forest virus. I: Low pH-induced rearrangement in spike protein quaternary structure precedes virus penetration into cells. J Cell Biol. 1992 Jan;116(2):339–348. [PMC free article] [PubMed]
  • White J, Helenius A. pH-dependent fusion between the Semliki Forest virus membrane and liposomes. Proc Natl Acad Sci U S A. 1980 Jun;77(6):3273–3277. [PMC free article] [PubMed]
  • White JM. Viral and cellular membrane fusion proteins. Annu Rev Physiol. 1990;52:675–697. [PubMed]
  • Ziemiecki A, Garofff H. Subunit composition of the membrane glycoprotein complex of Semliki Forest virus. J Mol Biol. 1978 Jul 5;122(3):259–269. [PubMed]
  • Ziemiecki A, Garoff H, Simons K. Formation of the Semliki Forest virus membrane glycoprotein complexes in the infected cell. J Gen Virol. 1980 Sep;50(1):111–123. [PubMed]

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