Focal accumulation of aromaticity at the CDRH3 loop mitigates 4E10 polyreactivity without altering its HIV neutralization profile

Distinctive Membrane Accommodation Traits Underpinning the Neutralization Activity of HIV-1 Antibody against MPER

The membrane-proximal external region (MPER), located in the carboxy-terminal section of HIV's envelope glycoprotein (Env) ectodomain, which is essential for viral entry into host cells, has gained considerable attention as a target for HIV vaccine development due to the exceptional neutralization breadth of antibodies against MPER epitopes. A distinctive feature of broadly neutralizing antibodies (bnAbs) targeting MPER is their requirement to accommodate the viral membrane into the surface of the antigen-binding fragment, or Fab moiety, to optimize antigen recognition. In this study, we sought to elucidate the molecular mechanism behind this interaction and its relevance to the antiviral function of bnAb 10E8. We conducted all-atom molecular dynamics simulations of three systems: (i) Fab 10E8 positioned on the surface of a viral-like lipid bilayer (VL-LB), (ii) Fab 10E8 in complex with an MPER helix anchored to the VL-LB via the Env glycoprotein transmembrane domain (TMD), and (iii) a Fab/MPER-TMD complex similarly embedded in the VL-LB but with a chemically optimized Fab 10E8 variant showing enhanced potency. Comparing these systems enabled us to derive atomic-scale Fab-membrane accommodation profiles pertinent to 10E8's neutralizing function. Our findings support that Fab adaptation to the viral membrane interface following epitope binding is crucial for developing MPER-targeted neutralizing activity. This analysis also provides insights into pathways for strengthening lipid interactions, which may prove valuable in designing MPER-based biologics and vaccines to prevent or treat HIV infection.

Binding Promiscuity of Therapeutic Factor VIII

The binding promiscuity of proteins defines their ability to indiscriminately bind multiple unrelated molecules. Binding promiscuity is implicated, at least in part, in the off-target reactivity, nonspecific biodistribution, immunogenicity, and/or short half-life of potentially efficacious protein drugs, thus affecting their clinical use. In this review, we discuss the current evidence for the binding promiscuity of factor VIII (FVIII), a protein used for the treatment of hemophilia A, which displays poor pharmacokinetics, and elevated immunogenicity. We summarize the different canonical and noncanonical interactions that FVIII may establish in the circulation and that could be responsible for its therapeutic liabilities. We also provide information suggesting that the FVIII light chain, and especially its C1 and C2 domains, could play an important role in the binding promiscuity. We believe that the knowledge accumulated over years of FVIII usage could be exploited for the development of strategies to predict protein binding promiscuity and therefore anticipate drug efficacy and toxicity. This would open a mutational space to reduce the binding promiscuity of emerging protein drugs while conserving their therapeutic potency.

Generation of a Nonbilayer Lipid Nanoenvironment after Epitope Binding Potentiates Neutralizing HIV-1 MPER Antibody

Establishment of interactions with the envelope lipids is a cardinal feature of broadly neutralizing antibodies (bnAbs) that recognize the Env membrane-proximal external region (MPER) of HIV. The lipid envelope constitutes a relevant component of the full "quinary" MPER epitope, and thus antibodies may be optimized through engineering their capacity to interact with lipids. However, the role of the chemically complex lipid nanoenvironment in the mechanism of MPER molecular recognition and viral neutralization remains poorly understood. To approach this issue, we computationally and experimentally investigated lipid interactions of broadly neutralizing antibody 10E8 and optimized versions engineered to enhance their epitope and membrane affinity by grafting bulky aromatic compounds. Our data revealed a correlation between neutralization potency and the establishment of favorable interactions with small headgroup lipids cholesterol and phosphatidylethanolamine, evolving after specific engagement with MPER. Molecular dynamics simulations of chemically modified Fabs in complex with an MPER-Transmembrane Domain helix supported the generation of a nanoenvironment causing localized deformation of the thick, rigid viral membrane and identified sphingomyelin preferentially occupying a phospholipid-binding site of 10E8. Together, these interactions appear to facilitate insertion of the Fabs through their engagement with the MPER epitope. These findings implicate individual lipid molecules in the neutralization function of MPER bnAbs, validate targeted chemical modification as a method to optimize MPER antibodies, and suggest pathways for MPER peptide-liposome vaccine development.

A two-step mechanism for the binding of the HIV-1 MPER epitope by the 10E8 antibody onto biosensor-supported lipid bilayers

HIV-1 antibodies targeting the carboxy-terminal area of the membrane-proximal external region (ctMPER) are close to exerting viral pan-neutralization. Here, we reconstituted the ctMPER epitope as the N-terminal extremity of the Env glycoprotein transmembrane domain helix and immobilized it onto biosensor-supported lipid bilayers. We assessed the binding mechanism of anti-MPER antibody 10E8 through Surface Plasmon Resonance, and found, through equilibrium and kinetic binding analyses as a function of bilayer thickness, peptide length, and paratope mutations, that 10E8 engages first with the epitope peptide (encounter), limited by ctMPER helix accessibility at the membrane surface, and then inserts into the lipid bilayer assisted by favorable Fab-membrane interactions (docking). This mechanistic information may help in devising new strategies to develop more efficient MPER-targeting vaccines.