CC BY 4.0 UnportedInsausti, SaraGarcia-Porras, MiguelTorralba, JohanaMorillo, IzaskunRamos-Caballero, Anderde la Arada, IgorApellaniz, BeatrizCaaveiro, Jose M. M.Carravilla, PabloEggeling, ChristianRujas, EdurneNieva, Jose L.2023-02-062023-02-062022https://oa.tib.eu/renate/handle/123456789/11242http://dx.doi.org/10.34657/10278Antibody engagement with the membrane-proximal external region (MPER) of the envelope glycoprotein (Env) of HIV-1 constitutes a distinctive molecular recognition phenomenon, the full appreciation of which is crucial for understanding the mechanisms that underlie the broad neutralization of the virus. Recognition of the HIV-1 Env antigen seems to depend on two specific features developed by antibodies with MPER specificity: (i) a large cavity at the antigen-binding site that holds the epitope amphipathic helix; and (ii) a membrane-accommodating Fab surface that engages with viral phospholipids. Thus, besides the main Fab–peptide interaction, molecular recognition of MPER depends on semi-specific (electrostatic and hydrophobic) interactions with membranes and, reportedly, on specific binding to the phospholipid head groups. Here, based on available cryo-EM structures of Fab–Env complexes of the anti-MPER antibody 10E8, we sought to delineate the functional antibody–membrane interface using as the defining criterion the neutralization potency and binding affinity improvements induced by Arg substitutions. This rational, Arg-based mutagenesis strategy revealed the position-dependent contribution of electrostatic interactions upon inclusion of Arg-s at the CDR1, CDR2 or FR3 of the Fab light chain. Moreover, the contribution of the most effective Arg-s increased the potency enhancement induced by inclusion of a hydrophobic-at-interface Phe at position 100c of the heavy chain CDR3. In combination, the potency and affinity improvements by Arg residues delineated a protein–membrane interaction site, whose surface and position support a possible mechanism of action for 10E8-induced neutralization. Functional delineation of membrane-interacting patches could open new lines of research to optimize antibodies of therapeutic interest that target integral membrane epitopes.enghttps://creativecommons.org/licenses/by/4.0570540anti-MPER HIV antibodyantibody–membrane interactionsbroadly neutralizing antibody 10E8HIV neutralizationMPER epitope recognitionprotein–membrane interactionsArticle