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"CHARACTERIZATION OF SEQUENCES IN THE V3 AND C4 REGIONS OF HIV-1 ENV THAT AFFECT OVERALL CONFORMATION AND EXPOSURE OF NEUTRALIZATION TARGETS"

by
Aidy Salomon
Interdisciplinary Biomedical Sciences Program
M.Sci. 2002, Graduate School of Biomedical Sciences-UMDNJ B.Sci. 2000, Ramapo College of NJ




Thesis Advisor: Abraham Pinter, Ph.D.
Professor
Department of Medicine

Wednesday, December 7, 2011
12:00 P.M., ICPH Auditorium


Abstract

Although the V3 domain of HIV-1 gp120 is usually masked in primary isolates and inaccessible to antibodies, V3 epitopes are extremely sensitive neutralization targets when exposed on the virion surface. The inherent neutralization sensitivities mediated by V3 sequences of different subtypes were compared by grafting various subtype-consensus V3 domains into the naturally unmasked SF162 Env backbone. Chimeras containing the consensus subtype C V3 sequence (V3C) were significantly more resistant to neutralization than the corresponding Env with the consensus subtype B V3 (V3B) sequence. This difference was seen for V3-specific monoclonal antibodies (mAbs) derived from infections with various HIV-1 subtypes that bound with equal affinities to the native V3B and V3C consensus sequences expressed as fusion proteins, and for mAbs directed against the CD4-binding domain, CD4-induced epitopes and the V1 domain, suggesting that the neutralization resistance induced by the ConC V3 sequence was due to a global masking effect. Three of the five amino acids differing between the subtype B and C V3 consensus sequences were found to contribute to this neutralization phenotype. In addition, single point mutations introduced at several conserved hydrophobic and charged sites in the V3C crown reversed the neutralization-resistant phenotype. The glycan proximal to the N-terminus of V3 slightly increased the neutralization resistance of Env. V3 exposure was strongly affected by specific sequences in C4, which altered the conformation of several chimeric Envs and Envs from primary isolates, leading to an increase in neutralization sensitivity to mAbs targeting the V3 and CD4-binding domains, while at the same time disrupting quaternary epitopes. Combinations of mutations in the V3 and C4 domains of a subtype C primary isolate revealed the existence of multiple conformations, including one in which the V3, CD4bd and QNEs are all simultaneously exposed. These results indicated that specific Env sequences influence the overall structure of native Env in a way that occludes multiple neutralization targets located both within and outside of the V3 domain. This effect presumably contributes to the differing neutralization resistance of primary isolates of different subtypes, and the understanding of the various conformations of Env may assist in the development of a potent, broadly neutralizing vaccine.


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