Fusion of enveloped viruses with cells and liposomes |
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Authors: | Shlomo Nir Nejat Düzgünes Maria C Pedroso De Lima Dick Hoekstra |
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Institution: | 1. The Seagram Centre for Soil and Water Sciences, Faculty of Agriculture, The Hebrew University of Jerusalem, 76100, Rehovot, Israel 2. Cancer Research Institute, USA 3. Department of Pharmaceutical Chemistry, University of California, 94143-0128, San Francisco, CA 4. Center for Cell Biology and the Department of Chemistry, University of Coimhra, 3049, Coimbra, Portugal 5. Laboratory of Physiological Chemistry, University of Groningen, Bloemsingel 10, 9712, KZ Groningen, The Netherlands
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Abstract: | The fusion of viruses with cells and liposomes is reviewed with focus on the analysis of the final extents and kinetics of
fusion.Influenza virus andSendai virus exhibit 100% of fusion capacity with cells at pH 5 and pH 7.5, respectively. On the other hand, there may be in certain
cases, a limit on the number of virions that can fuse with a single cell, that is significantly below the limit on binding.
It still remains to be resolved whether this limit reflects a limited number of possible fusion sites, or a saturation limit
on the amount of viral glycoproteins that can be incorporated in the cellular membrane, like the case of virus fusion with
pure phospholipid vesicles, in which the fusion products were shown to consist of a single virus and several liposomes. Both
viruses demonstrate incomplete fusion activity towards liposomes of a variety of compositions. In the case ofSendai virus, fusion inactive virions bind essentially irreversibly to liposomes. Yet, preliminary results revealed that such bound,
unfused virions can be released by sucrose gradient centrifugation. The separated unfused virions subsequently fuse when incubated
with a “fresh” batch of liposomes. We conclude, therefore, that the fraction of initially bound unfused virions does not consist
of dective particles, but rather of particles bound to liposomes via “inactive” sites.
Details of the low pH inactivation of fusion capacity ofinfluenza virus towards cells and liposomes are presented. This inactivation is caused by protonation and exposure of the hydrophobic
segment of HA2, and affects primarily the fusion rate constants. Some degree of inactivation also occurs when virions are bound to cellular
membranes. |
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Keywords: | Index Entries" target="_blank">Index Entries Virus fusion virus inactivation virus-cell fusion virus-liposome fusion membrane fusion influenza virus Sendai virus |
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