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Journal of Virology, October 2007, p. 11218-11225, Vol. 81, No. 20
0022-538X/07/$08.00+0     doi:10.1128/JVI.01256-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Fusion Induced by a Class II Viral Fusion Protein, Semliki Forest Virus E1, Is Dependent on the Voltage of the Target Cell{triangledown}

Ruben M. Markosyan,1 Margaret Kielian,2 and Fredric S. Cohen1*

Rush University Medical Center, Department of Molecular Biophysics and Physiology, Chicago, Illinois 60612,1 Albert Einstein College of Medicine, Department of Cell Biology, Bronx, New York 104612

Received 8 June 2007/ Accepted 27 July 2007

Cells expressing the low pH-triggered class II viral fusion protein E1 of Semliki Forest virus (SFV) were fused to target cells. Fusion was monitored by electrical capacitance and aqueous dye measurements. Electrical voltage-clamp measurements showed that SFV E1-induced cell-cell fusion occurred quickly after acidification for a trans-negative potential across the target membrane (i.e., negative potential inside the target cell) but that a trans-positive potential eliminated all fusion. Use of an ionophore to control potentials for a large population of cells confirmed the dependence of fusion on voltage polarity. In contrast, fusion induced by the class I fusion proteins of human immunodeficiency virus, avian sarcoma leukosis virus, and influenza virus was independent of the voltage polarity across the target cell. Initial pore size and pore growth were also independent of voltage polarity for the class I proteins. An intermediate of SFV E1-induced fusion was created by transient acidification at low temperature. Membranes were hemifused at this intermediate state, and raising the temperature at neutral pH allowed full fusion to occur. Capacitance measurements showed that maintaining a trans-positive potential definitely blocked fusion at steps following the creation of the hemifusion intermediate and may have inhibited fusion at prior steps. It is proposed that the trans-negative voltage across the endosomal membrane facilitates fusion after low-pH-induced conformational changes of SFV E1 have occurred.

* Corresponding author. Mailing address: Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1653 W. Congress Pkwy., Chicago, IL 60612. Phone: (312) 942-6753. Fax: (312) 942-8711. E-mail: fcohen{at}rush.edu

{triangledown} Published ahead of print on 8 August 2007.

Journal of Virology, October 2007, p. 11218-11225, Vol. 81, No. 20
0022-538X/07/$08.00+0     doi:10.1128/JVI.01256-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Berka, U., Khan, A., Blaas, D., Fuchs, R. (2009). Human Rhinovirus Type 2 Uncoating at the Plasma Membrane Is Not Affected by a pH Gradient but Is Affected by the Membrane Potential. J. Virol. 83: 3778-3787 [Abstract] [Full Text]  


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