Membrane binding is involved in the action of broadly neutralizing influenza antibodies.

Abstract

Influenza poses a major health issue globally. Characterized by annual epidemics with mild to severe symptoms and even a significant number of deaths, the virus has historically resulted in substantial economic and societal problems in the world. Neutralizing antibodies that bind to the membrane-proximal region of hemagglutinin (HA) provide considerable protection against the infection by blocking the fusion of virus to the host cell. Here, using an array of advanced modeling and simulation techniques employed to a very large molecular assembly, for the first time, we develop a high-resolution structural model of full-length, antibody-bound HA in a native viral membrane and describe key molecular interactions that determine the binding affinity of the antibody to the viral membrane. The model allowed us to identify key residues in the antibody that interact with and bind to the membrane. Guided by the simulation predictions, the virus neutralization activity of the antibody was evaluated by mutagenesis experiments and infectivity assays. In alignment with the simulation results, the experiments show that mutating the predicted basic residues located away from the antigen binding site in the antibody decreases the neutralizing activity by up to an order of magnitude. Based on the results, we propose that the direct interaction of membrane-proximal antibodies with the viral membrane plays a role in their neutralizing activity against the virus. Introducing additional basic side chains enhancing phospholipid-binding is expected to further stabilize the HA-antibody. Given the rapid evolution of the influenza virus, the developed model provides a framework for rational design and development of more effective therapeutic antibodies.