Broadly neutralizing antibodies (BNAb) to HIV-1 primarily target the conserved membrane proximal ectodomain region (MPER) of the viral gpl60 envelope protein. We have studied the HxB2 MPER segment in lipid environments by a combination of nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and surface plasmon resonance (SPR) methodologies. Structural analyses reveal a tilted N-terminal a-helix (aa 664-672) connected via a short hinge (673-674) to a fiat C-terminal helical segment (675-683), collectively forming a metastable L-shaped structure immersed in the membrane. The 4E10 BNAb extracts buried W672 and F673 following initial encounter with the surface embedded MPER while the 2F5 BNAb lifts up residues N-terminal to the hinge region, exposing L669 and W670. BNAb CDRH3 interactions with lipid appear critical for neutralizing activity of both BNAbs. These data have implications for vaccine design and suggest how BNAbs can perturb tryptophan residue associated viral fusion involving the MPER. Here we shall examine how other BNAbs or newly created MPER-binding antibodies induce conformational change around W672 and F673 or elsewhere using several distinct MPER segment sequences. We shall determine whether such structural changes upon antibody binding are linked to viral neutralization. Moreover, specificity and diversity of antibodies arising during natural HIV-1 infection vs. elicited upon vaccination will be compared. Sensitive EPR residue depth and inter-residue distance measurements will allow for relatively rapid screening of detectable changes in MPER conformation. Once identified by EPR, interaction will be followed by detailed NMR analysis. How lipid constituents of the virosome, including cholesterol, affect the membrane-embedded structure of the MPER, or its ability to undergo conformational changes upon antibody binding, will be assessed. In addition, lipid-enveloped nanoparticles as carriers of natively configured MPER segments, including those with a bioresorbable poly (lactide-co-glycolide)(PLGA) core harboring.
Given that globally, to date, 65 million human infections with HIV-1 have been estimated, the development of a vaccine eliciting broadly neutralizing antibodies in normal subjects will be an enormous preventive advance in the fight against AIDS.
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