利用冷冻电镜研究蛋白质机器的非平衡统计物理

Study of non-equilibrium statistical physics of protein machine by cryogenic electron microscopy

对蛋白质机器的完整描述应包括其微观结构、热力学和动力学性质与工作机制.最近兴起的冷冻电镜技术为蛋白质热力学与动力学的研究提供了全新的机遇.目前已经有一些工作不仅利用冷冻电镜技术解析蛋白质的高分辨率结构,还结合数据处理方法来分析蛋白质的构象分布并进一步推测其热力学性质.然而,利用冷冻电镜技术直接对蛋白质的动力学过程作观测与定量分析的方法还在发展的初级阶段.本文选取了一个理想的蛋白质系统,即蓝藻生物钟蛋白对冷冻电镜分析蛋白质非平衡过程的可能性进行探索.基于已有的实验数据,将蓝藻生物钟蛋白KaiC的平衡态统计物理模型推广至非平衡态,对KaiC蛋白处于非平衡态时的动力学特征进行预测.基于动力学预测结果,本文揭示了冷冻电镜技术具有分析蓝藻生物钟蛋白的非平衡过程的可能,为进一步的冷冻电镜实验提供了理论依据.

A comprehensive description of the protein should include its structure,thermodynamics,and kinetic properties.The recent rise of cryogenic electron microscopy(cryo-EM)provides new opportunities for the thermodynamic and kinetic research of proteins.There have been some researches in which cryo-EM is used not only to resolve the high-resolution structure of proteins but also to analyze the conformational distribution of proteins to infer their thermodynamic properties based on data processing methods.However,whether cryo-EM can be used to directly quantify the kinetics of proteins is still unclear.In this work,an ideal protein system,cyanobacterial circadian clock protein,is selected to explore the potential of cryo-EM used to analyze the nonequilibrium process of proteins.Previous research has illustrated that cryoelectron microscope can be used to infer the thermodynamic information about the KaiC protein such as the inter-subunit interaction within the hexamers.Herein,we extend the equilibrium Ising model of KaiC hexamers to a non-equilibrium statistical physics model,revealing the properties of the non-equilibrium process of KaiC hexamers.According to the nonequilibrium model and previous biochemical research,we find that the intrinsic properties of KaiC protein allow its non-equilibrium conformational distribution to be measured by cryo-EM.