Rare earth ions block the ion pores generated by the class II fusion proteins of alphaviruses and allow analysis of the biological functions of these pores

• Published in: Journal of general virology Vol. 86; no. 12; pp. 3311 - 3320
• Main Authors: Koschinski, Andreas, Wengler, Gerd, Wengler, Gisela, Repp, Holger
• Format: Journal Article
• Language: English
• Published: Reading Soc General Microbiol 01.12.2005; Society for General Microbiology
• Subjects: Alphavirus; Alphavirus - drug effects; Alphavirus - physiology; Biological and medical sciences; Calcium - metabolism; Fundamental and applied biological sciences. Psychology; Ion Channels - antagonists & inhibitors; Membrane Fusion Proteins - physiology; Membrane Potentials; Membrane Transport Modulators - pharmacology; Metals, Rare Earth - pharmacology; Microbiology; Miscellaneous; Patch-Clamp Techniques; Propidium - metabolism; Semliki Forest virus; Semliki forest virus - drug effects; Semliki forest virus - physiology; Sindbis virus; Sindbis Virus - drug effects; Sindbis Virus - physiology; Viral Plaque Assay; Virology; Virus Replication - drug effects; Microbiology; Fusion protein; Class II histocompatibility antigen; Virology
• ISSN: 0022-1317; 1465-2099
• DOI: 10.1099/vir.0.81096-0

1 Rudolf-Buchheim-Institut für Pharmakologie, Justus-Liebig-Universität, D-35392 Giessen, Germany 2 Institut für Virologie, Fachbereich Veterinärmedizin, Justus-Liebig-Universität, D-35392 Giessen, Germany Correspondence Gerd Wengler gerd.wengler{at}gmx.de Recently, class II fusion proteins have been identified on the surface of alpha- and flaviviruses. These proteins have two functions besides membrane fusion: they generate an isometric lattice on the viral surface and they form ion-permeable pores at low pH. An attempt was made to identify inhibitors for the ion pores generated by the fusion proteins of the alphaviruses Semliki Forest virus and Sindbis virus . These pores can be detected and analysed in three situations: (i) in the target membrane during virus entry, by performing patch-clamp measurements of membrane currents; (ii) in the virus particle, by studying the entry of propidium iodide; and (iii) in the plasma membrane of infected cells, by Fura-2 fluorescence imaging of Ca 2+ entry into infected cells. It is shown here that, at a concentration of 0·1 mM, rare earth ions block the ion permeability of alphavirus ion pores in all three situations. Even at a concentration of 0·5 mM, these ions do not block formation of the viral fusion pore, as they do not inhibit entry or multiplication of alphaviruses. The data indicate that ions flow through the ion pores into the virus particle in the endosome and from the endosome into the cytoplasm after fusion of the viral envelope with the endosomal membrane. These ion flows, however, are not necessary for productive infection. The possibility that the ability of class II fusion proteins to form ion-permeable pores reflects their origin from protein toxins that form ion-permeable pores, and that entry via class II fusion proteins may resemble the entry of non-enveloped viruses, is discussed. These authors contributed equally to this work.