In cell membranes, proteins and lipids diffuse in a highly crowded and heterogeneous landscape, where aggregates and dense domains of proteins or lipids obstruct the path of diffusing molecules. In general, hindered motion gives rise to anomalous transport, though the nature of the onset of this behavior is still under debate and difficult to investigate experimentally. Here, we present a systematic study where proteins bound to supported lipid membranes diffuse freely in two dimensions, but are increasingly hindered by the presence of other like proteins. In our model system, the surface coverage of the protein avidin on the lipid bilayer is well controlled by varying the concentration of biotinylated lipid anchors. Using fluorescence correlation spectroscopy (FCS), we measure the time correlation function over long times and convert it to the mean-square displacement of the diffusing proteins. Our approach allows for high precision data and a clear distinction between anomalous and normal diffusion. It enables us to investigate the onset of anomalous diffusion, which takes place when the area coverage of membrane proteins increases beyond approximately 5%. This transition region exhibits pronounced spatial heterogeneities. Increasing the packing fraction further, transport becomes more and more anomalous, manifested in a decrease of the exponent of subdiffusion.
Experiments and theories have shown that when steric interactions between crowding particles and proteins are dominant, which give rise to Asakura-Oosawa depletion forces, then the stabilities of the proteins increase compared to the infinite dilution case. We show using theoretical arguments that the crowder volume fraction ($Φ_C$) dependent increase in the melting temperature of globular proteins, $ΔT_m(Φ_C) \approx Φ_C^α$ where $α= \frac{1}{(3 ν_{eff} - 1)}$. The effective Flory exponent, $ν_{eff}$, relates the radius of gyration in the unfolded state to the number of amino acid residues in…
Diffusion in the crowded environments of the biological membranes or materials interfaces often involves intermittent binding to surface proteins or defects. To account for this situation we study a 2-dimensional lattice gas in a field of immobilized traps. Using kinetic Monte Carlo simulations, we calculate the effective diffusion coefficient in the long-time limit as a function of the traps and particle densities. We find a remarkable result - an increase of the diffusion coefficient with particle density, an effect that we coin as crowding-enhanced diffusion. We rationalize this result usin…
The diffusion of a particle in a crowded environment typically proceeds through three regimes: for very short times the particle diffuses freely until it collides with an obstacle for the first time, while for very long times diffusion the motion is Fickian with a diffusion coefficient $D$ that depends on the concentration and type of obstacles present in the system. For intermediate times, the mean-square displacement of the particle often increases approximately as $~t^α$, with $α<1$, typical of what is generally called anomalous diffusion. However, it is not clear how one can identify or ch…
在平均场模型的框架下研究了拥挤效应对稠密介质中标记粒子扩散的影响，该模型是在连续极限下从一个具有排斥的微观随机过程导出的.标记粒子的概率分布函数服从非线性Fokker-Planck方程，其中漂移和扩散项由介质中拥挤物的浓度自洽地确定。观察到瞬态亚扩散或超扩散行为，这取决于所选择的初始条件，桥梁正常的扩散制度，其特征在于不同的扩散系数。这些反常的交叉起源于空间的微观竞争，反映了福克-普朗克方程中非齐次平流项的特殊形式。我们的研究结果强烈警告过度简单化的拥挤与异常运输的识别{ \em tout court}。
Cell membranes interact with a myriad of curvature-active proteins that control membrane morphology and are responsible for mechanosensation and mechanotransduction. Some of these proteins, such as those containing BAR domains, are curved and elongated, and hence may adopt different states of orientational order, from isotropic to maximize entropy to nematic as a result of crowding or to adapt to the curvature of the underlying membrane. Here, extending the work of [Nascimento et. al, Phys. Rev. E, 2017, 96, 022704], we develop a mean-field density functional theory to predict the orientationa…
Characterizing anomalous diffusion in crowded polymer solutions and gels over five decades in time with variable-lengthscale fluorescence correlation spectroscopy
Actin cross-linking organizes basal body patterning through anomalous diffusion transitions
Novo Nordisk Foundation Center for Stem Cell Medicine (reNEW), Department of Biomedical Sciences, University of Copenhagen（哥本哈根大学生物医学科学系，诺和诺德基金会干细胞医学中心(reNEW)）；Biocomplexity, Niels Bohr Institute, Faculty of Science, University of Copenhagen（哥本哈根大学理学院尼尔斯·玻尔研究所生物复杂性研究中心）；Department of Civil Engineering, Indian Institute of Technology Bombay（印度孟买理工学院土木工程系）
Anomalous diffusion in coupled viscoelastic media: A fractional Langevin equation approach
Pohang University of Science and Technology（浦项科技大学）；Institute for Theoretical Science, Pohang University of Science and Technology（浦项科技大学理论科学研究所）；Asia Pacific Center for Theoretical Physics（亚太理论物理中心）
Most biological molecules contain acido-basic groups that modulate their structure and interactions. A consequence is that pH gradients, local heterogeneities and dynamic variations are used by cells and organisms to drive or regulate specific biological functions including energetic metabolism, vesicular traffic, migration and spatial patterning of tissues in development. While the direct or regulatory role of pH in protein function is well documented, the role of hydrogen and hydroxyl ions in modulating the properties of lipid assemblies such as bilayer membranes is only beginning to be unde…
Structure-Informed Bayesian Inference of Anomalous Transport and Hidden Molecular Trapping in Amorphous Media
Laboratory for Disordered Systems, Phystech School of Applied Mathematics and Computer Science, Moscow Institute of Physics and Technology（莫斯科物理技术学院应用数学与计算机科学普列特赫学院无序系统实验室）；Center for Computational Physics, Landau School for Physics and Research, Moscow Institute of Physics and Technology（莫斯科物理技术学院朗道物理与研究中心计算物理中心）
