Harnessing Avidity: Quantifying the Entropic and Energetic Effects of Linker Length and Rigidity for Multivalent Binding of Antibodies to HIV-1

IgG antibodies increase their apparent affinities by using both of their Fabs to simultaneously attach to antigens. HIV-1 foils this strategy by having few, and highly separated, Envelope (Env) spike targets for antibodies, forcing most IgGs to bind monovalently. Here, we develop a statistical mechanics model of synthetic diFabs joined by DNA linkers of different lengths and flexibilities. This framework enables us to translate the energetic and entropic effects of the linker into the neutralization potency of a diFab. We demonstrate that the strongest neutralization potencies are predicted to require a rigid linker that optimally spans the distance between two Fab binding sites on an Env trimer and that avidity can be further boosted by incorporating more Fabs into these constructs. These results inform the design of multivalent anti-HIV-1 therapeutics that utilize avidity effects to remain potent against HIV-1 in the face of the rapid mutation of Env spikes. [Display omitted] •Synthetic antibodies that bivalently bind to HIV-1 can markedly enhance avidity•Linkers that enable bivalent binding are fully characterized by the linker entropy•Properly sized rigid linkers outperform long, flexible linkers•Avidity can be further enhanced by increasing antibody valency Antibodies enhance their functional affinity by binding an antigen at multiple sites. Because HIV-1 contains few binding targets, the ability of antibodies to neutralize the virus is greatly decreased. Here, we develop a statistical-mechanical model that predicts the efficacy of synthetic antibodies composed of two Fabs joined together by DNA linkers of different lengths and flexibilities. This model predicts a synthetic antibody’s neutralization potency based on its linker composition, providing a framework to guide the design of future multivalent therapies.