Receptor Concentration and Diffusivity Control Multivalent Binding of Sv40 to Membrane Bilayers

Abstract
Incoming Simian Virus 40 particles bind to their cellular receptor, the glycolipid GM1, in the plasma membrane and thereby induce membrane deformation beneath the virion leading to endocytosis and infection. Efficient membrane deformation depends on receptor lipid structure and the organization of binding sites on the internalizing particle. To determine the role of receptor diffusion, concentration and the number of receptors required for stable binding in this interaction, we analyze the binding of SV40 to GM1 in supported membrane bilayers by computational modeling based on experimental data. We measure the diffusion rates of SV40 virions in solution by fluorescence correlation spectroscopy and of the receptor in bilayers by single molecule tracking. Quartz-crystal microbalance with dissipation (QCM-D) is used to measure binding of SV40 virus-like particles to bilayers containing the viral receptor GM1. We develop a phenomenological stochastic dynamics model calibrated against this data, and use it to investigate the early events of virus attachment to lipid membranes. Our results indicate that SV40 requires at least 4 attached receptors to achieve stable binding. We moreover find that receptor diffusion is essential for the establishment of stable binding over the physiological range of receptor concentrations and that receptor concentration controls the mode of viral motion on the target membrane. Our results provide quantitative insight into the initial events of virus-host interaction at the nanoscopic level.

摘要
侵入的猿猴病毒40（Simian Virus 40, SV40）颗粒可在质膜中结合其细胞受体——糖脂GM1，进而诱导病毒粒子下方的膜形变，最终引发内吞作用与感染。高效的膜形变依赖于受体的脂质结构以及内吞粒子上结合位点的组织排布。为明确该相互作用中受体扩散、浓度与稳定结合所需受体数量所扮演的角色，本研究基于实验数据，通过计算建模分析了支撑膜双层中SV40与GM1的结合过程。研究人员借助荧光相关光谱（fluorescence correlation spectroscopy, FCS）测定了溶液中SV40病毒粒子的扩散速率，并通过单分子追踪技术测定了双层膜内受体的扩散速率。本研究采用耗散型石英晶体微天平（Quartz-crystal microbalance with dissipation, QCM-D）技术，检测了SV40病毒样颗粒与携带病毒受体GM1的双层膜的结合情况。我们构建了基于上述实验数据校准的现象学随机动力学模型，并利用该模型探究了病毒附着于脂质膜的早期事件。研究结果表明，SV40至少需要4个结合的受体方可实现稳定结合。此外，本研究发现，在受体浓度的生理范围内，受体扩散对稳定结合的形成至关重要，且受体浓度可调控病毒在靶膜上的运动模式。本研究结果为从纳米尺度解析病毒-宿主相互作用的初始事件提供了定量视角。