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Journal of Virology, November 2009, p. 11005-11015, Vol. 83, No. 21
0022-538X/09/$08.00+0     doi:10.1128/JVI.01238-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Adaptive Mutations in a Human Immunodeficiency Virus Type 1 Envelope Protein with a Truncated V3 Loop Restore Function by Improving Interactions with CD4

Caroline Agrawal-Gamse,¹ Fang-Hua Lee,¹ Beth Haggarty,² Andrea P. O. Jordan,² Yanjie Yi,² Benhur Lee,³ Ronald G. Collman,² James A. Hoxie,² Robert W. Doms,^1* and Meg M. Laakso¹

Departments of Microbiology,¹ Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104,² Department of Microbiology, Immunology, and Molecular Genetics, University of California at Los Angeles, Los Angeles, California 90095³³

Received 15 June 2009/ Accepted 6 August 2009

We previously reported that a human immunodeficiency virus type 1 (HIV-1) clade B envelope protein with a severely truncated V3 loop regained function after passage in tissue culture. The adapted virus, termed TA1, retained the V3 truncation, was exquisitely sensitive to neutralization by the CD4 binding site monoclonal antibody b12 and by HIV-positive human sera, used CCR5 to enter cells, and was completely resistant to small molecule CCR5 antagonists. To examine the mechanistic basis for these properties, we singly and in combination introduced each of the 5 mutations from the adapted clone TA1 into the unadapted envelope. We found that single amino acid changes in the C3 region, the V3 loop, and in the fusion peptide were responsible for imparting near-normal levels of envelope function to TA1. T342A, which resulted in the loss of a highly conserved glycosylation site in C3, played the primary role. The adaptive amino acid changes had no impact on CCR5 antagonist resistance but made virus more sensitive to neutralization by antibodies to the CD4 binding site, modestly enhanced affinity for CD4, and made TA1 more responsive to CD4 binding. Specifically, TA1 was triggered by soluble CD4 more readily than the parental Env and, unlike the parental Env, could mediate entry on cells that express low levels of CD4. In contrast, TA1 interacted with CCR5 less efficiently and was highly sensitive to antibodies that bind to the CCR5 N terminus and ECL2. Therefore, enhanced utilization of CD4 is one mechanism by which HIV-1 can overcome mutations in the V3 region that negatively affect CCR5 interactions.

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* Corresponding author. Mailing address: 3610 Hamilton Walk, 225A Johnson Pavilion, University of Pennsylvania, Philadelphia, PA 19104. Phone: (215) 573-6780. Fax: (215) 898-9557. E-mail: doms{at}mail.med.upenn.edu

Published ahead of print on 19 August 2009.

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Journal of Virology, November 2009, p. 11005-11015, Vol. 83, No. 21
0022-538X/09/$08.00+0     doi:10.1128/JVI.01238-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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