Abstract
BackgroundHIV-1 Env gp160 is cleaved to form gp120 and gp41 and the functional HIV-1 Env is a trimer of non-covalently associated heterodimeric subunits, gp120 and gp41. The cleaved, native, trimeric form of Envs expose only broadly neutralizing antibody (bNAb) epitopes while occluding epitopes targeted by non-neutralizing antibodies (non-NAbs). We and others have previously observed that efficient cleavage of Envs into their constituent subunits co-relates with specific binding to bNAbs and poor binding to non-neutralizing antibodies (non-NAbs). Such Envs have been identified from clades A, B and C which make up a majority of globally circulating HIV-1 strains. Frequently, the C-terminal tail (CT) of Envs is deleted to enhance expression and stabilize soluble Env-based vaccine immunogens. Deletion of CT of efficiently cleaved Indian clade C Env 4-2.J41 results in recognition by both NAbs and non-NAbs. It is to be noted that uncleaved Envs bind to both NAbs and non-NAbs. So we investigated whether altered antigenicity upon CT deletion of efficiently cleaved Envs is due to inefficient cleavage or conformational change as the mechanism by which the CT regulates the ectodomain (ET) integrity is not well understood.ResultsWe studied the effect of CT deletion in four membrane bound efficiently cleaved Envs, A5 (clade A), 4-2.J41 (clade C), JRFL and JRCSF (clade B). Deletion of CT of the Envs, JRCSF and 4-2.J41, but not JRFL and A5 alter their ET antigenicity/conformation without affecting the cleavage efficiency. We carried out a series of deletion mutation in order to determine the region of the CT required for restoring native-like antigenicity/conformation of the ET of 4-2.J41 and JRCSF. Extending the CT up to aa753 in 4-2.J41 and aa759 in JRCSF, which includes a conserved hydrophilic domain (CHD), restores native-like conformation of these Envs on the plasma membrane. However, CT-deletion in 4-2.J41 and JRCSF at the pseudovirus level has either no or only modest effect on neutralization potency.ConclusionHere, we report that the CHD in the CT of Env plays an important role in regulating the ET integrity of a subset of efficiently cleaved, functional Envs on the cell surface.
Highlights
human immunodeficiency virus type I (HIV-1) Env gp160 is cleaved to form gp120 and gp41 and the functional HIV-1 Env is a trimer of noncovalently associated heterodimeric subunits, gp120 and gp41
C terminal tail deletion of 4‐2.J41 affects ectodomain conformation/antigenicity It has been reported previously that truncation of the C-terminus of HIV-1 Envs generally leads to higher expression but affects their antigenicity, which is evident from exposure of epitopes for non-neutralizing antibodies [28,29,30,31,32]
In order to directly compare the effect of C-terminal tail (CT) deletion of JRFL, JRCSF and A5 on its binding to broadly neutralizing antibody (bNAb) and non-neutralizing antibody (non-NAb) and to investigate whether the CD4 induced (CD4i) and immunodominant V3 epitopes are exposed in ΔCT versions of these Envs, we studied their binding to the bNAb, PGT145 and non-NAbs, 17b and 19b (Fig. 6b, d, f )
Summary
HIV-1 Env gp160 is cleaved to form gp120 and gp and the functional HIV-1 Env is a trimer of noncovalently associated heterodimeric subunits, gp120 and gp. We and others have previously observed that efficient cleavage of Envs into their constituent subunits co-relates with specific binding to bNAbs and poor binding to non-neutralizing antibodies (non-NAbs). Such Envs have been identified from clades A, B and C which make up a majority of globally circulating HIV-1 strains. In order to use Envs as immunogens for DNA, viral vector, virus-like particle based vaccination studies, it is essential that they are efficiently cleaved and display only broadly neutralizing epitopes on the cell surface. Envs belonging to clades A, B and C make up about 75% of globally circulating HIV-1 strains
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