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Journal of Virology, January 2004, p. 508-512, Vol. 78, No. 1
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.1.508-512.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

An Aromatic Side Chain Is Required at Residue 8 of SU for Fusion of Ecotropic Murine Leukemia Virus

Zhaohui Qian and Lorraine M. Albritton*

Department of Molecular Sciences, University of Tennessee Health Science Center, Memphis, Tennessee 38163

Received 12 December 2002/ Accepted 26 September 2003

The surface glycoprotein (SU) of most gammaretroviruses contains a conserved histidine at its amino terminus. In ecotropic murine leukemia virus SU, replacement of histidine 8 with arginine (H8R) or deletion of H8 (H8del) abolishes infection and cell-cell fusion but has no effect on binding to the cellular receptor. We report here that an aromatic ring side chain is essential to the function of residue 8. The size of the aromatic ring appears to be important, as does its ability to form a hydrogen bond. In addition, infection by all of the nonaromatic amino acid substitutions could be partially rescued by the addition of two suppressor mutations (glutamine 227 to arginine [Q227R] and aspartate 243 to tyrosine [D243Y]) or by exposure to chlorpromazine, an agent that induces fusion pores in hemifusion intermediates to complete fusion, suggesting that, like the previously described H8R mutant, the mutants reported here also arrest membrane fusion at the hemifusion state. We propose that H8 is a key switch-point residue in the conformation changes that lead to membrane fusion and present a possible mechanism for how its substitution arrests fusion at the hemifusion state.

* Corresponding author. Mailing address: Department of Molecular Science, University of Tennessee Health Science Center, 858 Madison Ave., Rm. G01, Memphis, TN 38163. Phone: (901) 448-5521. Fax: (901) 448-7360. E-mail: lalbritton{at}utmem.edu.

Journal of Virology, January 2004, p. 508-512, Vol. 78, No. 1
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.1.508-512.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.





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