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Journal of Virology, April 2004, p. 3223-3232, Vol. 78, No. 7
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.7.3223-3232.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Amino Acid 324 in the Simian Immunodeficiency Virus SIVmac V3 Loop Can Confer CD4 Independence and Modulate the Interaction with CCR5 and Alternative Coreceptors

Stefan Pöhlmann,^1,2,3* Carl Davis,¹ Silke Meister,^2,3 George J. Leslie,¹ Claas Otto,⁴ Jacqueline D. Reeves,¹ Bridget A. Puffer,¹ Armin Papkalla,² Mandy Krumbiegel,² Andrea Marzi,^2,3 Steffen Lorenz,⁴ Jan Münch,⁴ Robert W. Doms,¹ and Frank Kirchhoff⁴

Department of Microbiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104,¹ Institute for Clinical and Molecular Virology,² Nikolaus-Fiebiger-Zentrum, University Erlangen-Nürnberg, 91054 Erlangen,³ Abteilung Virologie-Universitätsklinikum, 89081 Ulm, Germany⁴

Received 22 August 2003/ Accepted 22 December 2003

The V3 loop of the simian immunodeficiency virus (SIV) envelope protein (Env) largely determines interactions with viral coreceptors. To define amino acids in V3 that are critical for coreceptor engagement, we functionally characterized Env variants with amino acid substitutions at position 324 in V3, which has previously been shown to impact SIV cell tropism. These changes modulated CCR5 engagement and, in some cases, allowed the efficient usage of CCR5 in the absence of CD4. The tested amino acid substitutions had highly differential effects on viral infectivity. Eleven of sixteen substitutions disrupted entry via CCR5 or the alternative coreceptor GPR15. Nevertheless, most of these variants replicated in the macaque T-cell line 221-89 and some also replicated in rhesus macaque peripheral blood monocytes, suggesting that efficient usage of CCR5 and GPR15 on cell lines is not a prerequisite for SIV replication in primary cells. Four variants showed enhanced entry into the macaque sMagi reporter cell line. However, sMagi cells did not express appreciable amounts of CCR5 and GPR15 mRNA, and entry into these cells was not efficiently blocked by a small-molecule CCR5 antagonist, suggesting that sMagi cells express as-yet-unidentified entry cofactors. In summary, we found that a single amino acid at position 324 in the SIV Env V3 loop can modulate both the efficiency and the types of coreceptors engaged by Env and allow for CD4-independent fusion in some cases.

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* Corresponding author. Mailing address: Institute for Clinical and Molecular Virology, University Erlangen-Nürnberg, Schlossgarten 4, D-91054 Erlangen, Germany. Phone: 49-9131-8529142. Fax: 49-9131-8529111. E-mail: snpoehlm{at}viro.med.uni-erlangen.de.

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Journal of Virology, April 2004, p. 3223-3232, Vol. 78, No. 7
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.7.3223-3232.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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