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J. Virol., 02 1995, 695-700, Vol 69, No. 2
SL Allison, J Schalich, K Stiasny, CW Mandl, C Kunz and FX Heinz
The flavivirus envelope protein E undergoes irreversible conformational
changes at a mildly acidic pH which are believed to be necessary for
membrane fusion in endosomes. In this study we used a combination of
chemical cross-linking and sedimentation analysis to show that the envelope
proteins of the flavivirus tick-borne encephalitis virus also change their
oligomeric structure when exposed to a mildly acidic environment. Under
neutral or slightly alkaline conditions, protein E on the surface of native
virions exists as a homodimer which can be isolated by solubilization with
the nonionic detergent Triton X-100. Solubilization with the same detergent
after pretreatment at an acidic pH, however, yielded homotrimers rather
than homodimers, suggesting that exposure to an acidic pH had induced a
simultaneous weakening of dimeric contacts and a strengthening of trimeric
ones. The pH threshold for the dimer-to-trimer transition was found to be
6.5. Because the pH dependence of this transition parallels that of
previously observed changes in the conformation and hydrophobicity of
protein E and that of virus-induced membrane fusion, it appears likely that
the mechanism of fusion with endosomal membranes involves a specific
rearrangement of the proteins in the viral envelope. Immature virions in
which protein E is associated with the uncleaved precursor (prM) of the
membrane protein M did not undergo a low-pH-induced rearrangement. This is
consistent with a protective role of protein prM for protein E during
intracellular transport of immature virions through acidic compartments of
the trans-Golgi network.
Copyright © 1995, American Society for Microbiology
Oligomeric rearrangement of tick-borne encephalitis virus envelope proteins induced by an acidic pH
Institute of Virology, University of Vienna, Austria.
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