Filament rigidity causes F-actin depletion from nonbinding surfaces
Filament rigidity causes F-actin depletion from nonbinding surfaces
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DOI：
10.1073/pnas.0804991106
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发表时间：
2009-01-06
影响因子：
11.1
通讯作者：
Kuo, Scot C.
中科院分区：
文献类型：
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作者：
Fisher, Charles I.;Kuo, Scot C.
肌动蛋白网络的许多关键细胞功能，包括力学和运动性，都需要接近细胞膜。然而，F-肌动蛋白的刚性应该阻碍细丝接近表面。使用共聚焦显微镜，我们监测附近的非粘附玻璃表面的荧光肌动蛋白的分布。最初均匀，单体聚集以产生耗尽区，其中F-肌动蛋白在表面不存在，但随着与表面的距离单调增加。在最大的情况下，损耗效应可以延伸到35 μ m以上，与平均的质量加权细丝长度相当。用鬼笔环肽增加肌动蛋白丝的刚性会增加耗尽的程度，而用加帽蛋白缩短肌动蛋白丝会按比例降低耗尽的程度。此外，消耗动力学是更快的肌动蛋白浓度，与更快的聚合和更快的布朗棘轮驱动的运动。相反，耗尽的程度随着肌动蛋白浓度的增加而降低，这表明熵是热力学驱动力。定量，耗尽动力学和程度匹配现有的肌动蛋白动力学，刚度和长度。然而，解释耗尽曲线和浓度依赖性（-1的幂律）需要修改刚性棒模型。在细胞内，表面耗竭应使膜相关的F-肌动蛋白反应比流体动力学减慢的细丝扩散（大约10倍）慢另外大约10倍。此外，表面消耗应导致膜自发地向细丝弯曲。这种消耗原理是所有与机械结构相关的表面反应的热力学基础，从DNA到细丝再到网络。对于各种功能，细胞必须积极抵抗消耗的热力学。
Proximity to membranes is required of actin networks for many key cell functions, including mechanics and motility. However, F-actin rigidity should hinder a filament's approach to surfaces. Using confocal microscopy, we monitor the distribution of fluorescent actin near nonadherent glass surfaces. Initially uniform, monomers polymerize to create a depletion zone where F-actin is absent at the surface but increases monotonically with distance from the surface. At its largest, depletion effects can extend >35 mu m, comparable with the average, mass-weighted filament length. Increasing the rigidity of actin filaments with phalloidin increases the extent of depletion, whereas shortening filaments by using capping protein reduces it proportionally. In addition, depletion kinetics are faster with higher actin concentrations, consistent with faster polymerization and faster Brownian-ratchet-driven motion. Conversely, the extent of depletion decreases with actin concentration, suggesting that entropy is the thermodynamic driving force. Quantitatively, depletion kinetics and extent match existing actin kinetics, rigidity, and lengths. However, explaining depletion profiles and concentration dependence (power-law of -1) requires modifying the rigid rod model. Within cells, surface depletion should slow membrane-associated F-actin reactions another approximate to 10-fold beyond hydrodynamically slowed diffusion of filaments (approximate to 10-fold). In addition, surface depletion should cause membranes to bend spontaneously toward filaments. Such depletion principles underlie the thermodynamics of all surface-associated reactions with mechanical structures, ranging from DNA to filaments to networks. For various functions, cells must actively resist the thermodynamics of depletion.