pH-dependent fusion of tick-borne encephalitis virus with artificial membranes

Abstract

pH-dependent fusion of TBE virus with artificial membranes was effective at slightly acidic pH with maximum at 6.4. The influence of various changes in E protein conformation on fusion process was studied.

Structures and mechanisms in flavivirus fusion

“…The pH threshold for triggering the low pH-induced structural changes in TBE virus correlates with that of the induction of fusion activity, suggesting that these processes are closely linked. A threshold around pH 6.6 was found for both the changes in monoclonal antibody (MAb) reactivity and the dimer-trimer transition (Allison et al, 1995a), and this corresponds to the threshold for the induction of fusion in cell-cell fusion assays (Guirakhoo et al, 1991) and for virus fusion with artificial liposomal membranes (Vorovitch et al, 1991;Corver et al, 2000). Somewhat higher pH thresholds for both the conformational change and fusion have been reported for other flaviviruses (Gollins and Porterfield, 1986b;Kimura and Ohyama, 1988;Summers et al, 1989;Guirakhoo et al, 1993).…”

“…The fusion properties of flaviviruses have been investigated using several different assay systems, including virus-induced cell-cell fusion and virus-liposome fusion (Ueba and Kimura, 1977;Gollins and Porterfield, 1986b;Summers et al, 1989;Randolph and Stollar, 1990a;Guirakhoo et al, 1991;Vorovitch et al, 1991;Despres et al, 1993;Guirakhoo et al, 1993;Corver et al, 1999). All of these studies indicate that flaviviruses require an acidic pH for fusion, consistent with their proposed mode of entry.…”

“…With flaviviruses there appears, in some instances, to be a good correlation between fusion inhibition and neutralization, most notably in the case of the domain II-specific neutralizing antibodies A3 and A4 for TBE virus (Guirakhoo et al, 1991) (Schalich et al, in preparation) and 4E5 and 1B7 for DEN 2 virus (Roehrig et al, 1998). The TBE virus MAbs A1, A2, , 14D2 (Volkova et al, 1999), and Gll (Vorovitch et al, 1991), however, are nonneutralizing, although they can completely inhibit fusion in vitro. The most likely explanation for these seemingly paradoxical results is that these MAbs do not bind well to the native infectious virus as it exists outside the cell, but instead recognize cryptic epitopes that become accessible only after the virus has entered the endosome and the low pH-induced structural changes have occurred.…”

Recombinant subviral particles from tick-borne encephalitis virus are fusogenic and provide a model system for studying flavivirus envelope glycoprotein functions

“…Low-pH-dependent functions of membrane fusion and hemagglutination. TBE virus-mediated membrane fusion requires an acidic pH (10,38), and it is believed that this pH dependence is related to the ability to undergo the low-pH-induced structural rearrangements described above. To test whether RSPs exhibit fusion activity, a fusion from without (FFWO) assay with the C6/36 mosquito cell line was employed (10).…”

“…The two oligomeric states of the TBE virus E protein reflect the bifunctional nature of this protein and its role in both receptor binding and acidinduced fusion (35). The native dimeric configuration is probably required for recognition of a still-unidentified cellular receptor, whereas conversion to the trimeric form at low pH appears to be necessary for membrane fusion (2,10,16,38).…”