Biomechanical Characterization of Ligand-receptor Mediated Ebola Virus Host Entry Mechanism using Atomic Force Microscopy

ABSTRACTThe emergence of Ebola virus disease (EVD) in Africa has caused significant mortality in recent years. Ebola virus (EBOV) is a filamentous, negative-sense, single stranded RNA virus that can infect mammalian species through direct blood and body fluids transmission, causing deadly hemorrhagic fever. The entry of EBOV into human body is thought to be mediated by a specific ligand-receptor binding mechanism. A group of PS binding proteins are identified to bind with the lipid phosphatidylserine (PS) expressed on the EBOV viral envelope. Despite the findings which uncovered the biological functions and structures of these protein receptors, the biophysics of the PVEER-EBOV interactions such as the mechanical strength of the bond formed between EBOV PS and PVEERs and how well these bonds resist external mechanical perturbations are vaguely understood. Here, we use atomic force microscopy (AFM) to conduct single molecular analysis and quantify the unbinding forces between PS and a group of selected PS binding proteins (TIM-1, Protein S, Gas6 and MFG-E8). We have also utilized a PS-expressing EBOV model system: the viral like particle (VLP) which closely resembles the biological structures and behaviors of EBOV without inducing pathogenicity. Bell-Evans model is applied to examine the reaction kinetics of the interactions between PS/VLP and PS binding proteins. By comparing the mechanical strength and reaction kinetics between PS binding proteins and PS or VLP, we have demonstrated that each receptor protein tested possesses distinct mechanical property during the interaction with its ligand and each could play a very crucial role in mediating EBOV internalization. However, MFG-E8 has the most robust bond strength and overall better bio-mechanical performance during the interaction. The magnitude of force, reaction kinetics of the PS biding protein with PS and VLP are all consistent and comparable with previous AFM single molecular studies about virus and host cell interaction. Our results enable deeper understandings of the physical properties of EBOV internalization mechanism and could potentially contribute to the future development of possible vaccine for EVD treatment.