Research

The carbohydrate at asparagine 386 on HIV-1 gp120 is not essential for protein folding and function but is involved in immune evasion

Rogier W Sanders¹ , Eelco van Anken^2,3 , Alexei A Nabatov^1,4 , I Marije Liscaljet^2,5 , Ilja Bontjer¹ , Dirk Eggink¹ , Mark Melchers¹ , Els Busser¹ , Martijn M Dankers¹ , Fedde Groot^1,6 , Ineke Braakman² , Ben Berkhout¹ and William A Paxton¹

¹  Laboratory of Experimental Virology, Dept. Medical Microbiology, Center of Infection and Immunity Amsterdam (CINIMA), Academic Medical Center of the University of Amsterdam, Amsterdam, The Netherlands

²  Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands

³  Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158-2517, USA

⁴  Department of Molecular Cell Biology and Immunology, VU University Medical Center, van de Boechorstraat 7, 1081 BT Amsterdam, The Netherlands

⁵  Crucell, Archimedesweg 4, 2333 CN Leiden, The Netherlands

⁶  Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK

author email corresponding author email

Retrovirology 2008, 5:10doi:10.1186/1742-4690-5-10

Published:	31 January 2008

Abstract

Background

The HIV-1 envelope glycoprotein gp120, which mediates viral attachment to target cells, consists for ~50% of sugar, but the role of the individual sugar chains in various aspects of gp120 folding and function is poorly understood. Here we studied the role of the carbohydrate at position 386. We identified a virus variant that had lost the 386 glycan in an evolution study of a mutant virus lacking the disulfide bond at the base of the V4 domain.

Results

The 386 carbohydrate was not essential for folding of wt gp120. However, its removal improved folding of a gp120 variant lacking the 385–418 disulfide bond, suggesting that it plays an auxiliary role in protein folding in the presence of this disulfide bond. The 386 carbohydrate was not critical for gp120 binding to dendritic cells (DC) and DC-mediated HIV-1 transmission to T cells. In accordance with previous reports, we found that N386 was involved in binding of the mannose-dependent neutralizing antibody 2G12. Interestingly, in the presence of specific substitutions elsewhere in gp120, removal of N386 did not result in abrogation of 2G12 binding, implying that the contribution of N386 is context dependent. Neutralization by soluble CD4 and the neutralizing CD4 binding site (CD4BS) antibody b12 was significantly enhanced in the absence of the 386 sugar, indicating that this glycan protects the CD4BS against antibodies.

Conclusion

The carbohydrate at position 386 is not essential for protein folding and function, but is involved in the protection of the CD4BS from antibodies. Removal of this sugar in the context of trimeric Env immunogens may therefore improve the elicitation of neutralizing CD4BS antibodies.