Table S1. Mutations with known phenotypes in dengue virus and possible explanations based on the structures of sE of dengue virus types 2 and 3. Residue numbers refer to dengue virus type 2. For unconserved residues, the residue type in dengue 2 is listed in brackets before the residue number. Residues that are unconserved among dengue serotypes are in bold.

Mutation / Serotype / Phenotype / Explanation
N153E, T155I / DEN-2, DEN-4, TBE/DEN-4 chimera / Fusion occurs at pH > 6.5; less virulent; more neurovirulent in mice / Prevents glycosylation at 153, in domain I (2, 5, 11).
F193V / DEN-3 (passaged) / Fusion pH threshold 0.9 pH units lower. / Forms part of hydrophobic pocket under the kl hairpin. Shorter side chain may favor closed form of kl hairpin (6, 10).
F193L / DEN-3 (passaged) / Fusion pH threshold 0.2 pH units lower. / As above (6, 10).
K204R / DEN-3 (passaged) / Fusion pH threshold 0.7 pH units lower. / May strengthen dimer interface near kl hairpin (6, 10).
I270V/S / DEN-3 (passaged) / Fusion pH threshold 0.7 pH units lower. / Shorter side chains may favor closed form of kl hairpin (6, 10).
F279S / DEN-3 (passaged), DEN-1 / Fusion pH threshold 0.7 pH units lower; more virulent and hemagglutinating at pH 5.8-7. Escapes neutralization by IgM M10. / At base of kl hairpin. Van der Waals contacts of Phe favor open form; shorter side chains favor closed form of the kl hairpin (1, 6, 10).

T293I

/ DEN-1 / More virulent and hemagglutinating at pH 5.8-7; escapes neutralization by IgM M17. / At a hinge between domains I and III. May rigidify the hinge, requiring lower pH for conformational switch (1).

K307E

/ DEN-2 / Escapes neutralization by IgG G8D11. / IgG G8D11 may interfere with receptor binding (8).
E311G / DEN-2 / Escapes neutralization by IgM 6B2. / IgM 6B2 may interfere with receptor binding (9).

E383G

P384E/D/N

G385K/S/A

/ DEN-2 / Escape neutralization by IgG 3H5. Reduced mouse neurovirulence. / IgG 3H5 may interfere with receptor binding (3), probably in mosquito cells and not in human cells (4).

D390H

/ DEN2 (Mexican strain) / Less virulent, but more neurovirulent in mice. / Reversal of charge may interfere with receptor binding (12).

D390N

/ DEN-2 (Mexican strain) / More prone to hemorrhagic fever (less neurovirulent). / Neutralization of charge may enhance receptor binding (7).

REFERENCES

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2.Guirakhoo, F., A. R. Hunt, J. G. Lewis, and J. T. Roehrig. 1993. Selection and partial characterization of dengue 2 virus mutants that induce fusion at elevated pH. Virology 194:219-223.

3.Hiramatsu, K., M. Tadano, R. Men, and C. J. Lai. 1996. Mutational analysis of a neutralization epitope on the dengue type 2 virus (DEN2) envelope protein: monoclonal antibody resistant DEN2/DEN4 chimeras exhibit reduced mouse neurovirulence. Virology 224:437-445.

4.Hung, J. J., M. T. Hsieh, M. J. Young, C. L. Kao, C. C. King, and W. Chang. 2004. An external loop region of domain III of dengue virus type 2 envelope protein is involved in serotype-specific binding to mosquito but not mammalian cells. J. Virol. 78:378-388.

5.Kawano, H., V. Rostapshov, L. Rosen, and C. J. Lai. 1993. Genetic determinants of dengue type 4 virus neurovirulence for mice. J. Virol. 67:6567-6575.

6.Lee, E., R. C. Weir, and L. Dalgarno. 1997. Changes in the dengue virus major envelope protein on passaging and their localization on the three-dimensional structure of the protein. Virology 232:281-290.

7.Leitmeyer, K. C., D. W. Vaughn, D. M. Watts, R. Salas, I. Villalobos, C. de, C. Ramos, and R. Rico-Hesse. 1999. Dengue virus structural differences that correlate with pathogenesis. J. Virol. 73:4738-4747.

8.Lin, B., C. R. Parrish, J. M. Murray, and P. J. Wright. 1994. Localization of a neutralizing epitope on the envelope protein of dengue virus type 2. Virology 202:885-890.

9.Lok, S. M., M. L. Ng, and J. Aaskov. 2001. Amino acid and phenotypic changes in dengue 2 virus associated with escape from neutralisation by IgM antibody. J. Med. Virol. 65:315-323.

10.Modis, Y., and S. C. Harrison. 2003. A ligand-binding pocket in the dengue virus envelope glycoprotein. Proc. Natl. Acad. Sci. USA 100:6986-6991.

11.Pletnev, A. G., M. Bray, and C. J. Lai. 1993. Chimeric tick-borne encephalitis and dengue type 4 viruses: effects of mutations on neurovirulence in mice. J. Virol. 67:4956-4963.

12.Sanchez, I. J., and B. H. Ruiz. 1996. A single nucleotide change in the E protein gene of dengue virus 2 Mexican strain affects neurovirulence in mice. J. Gen. Virol. 77:2541-2545.