Modeling of the elongation and retraction of Escherichia coli P pili under strain by Monte Carlo simulations
Modeling of the elongation and retraction of Escherichia coli P pili under strain by Monte Carlo simulations
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DOI：
10.1007/s00249-007-0223-6
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发表时间：
2008-04-01
影响因子：
2
通讯作者：
Andersson, Magnus
中科院分区：
文献类型：
--
作者：
Bjornham, Oscar;Axner, Ove;Andersson, Magnus
P菌毛是上尿路致病性大肠埃希菌表达的菌毛粘附器。它们构成了一种刚性的螺旋状聚合物，由许多通过头尾键连接的亚基组成。用蒙特卡罗(MC)模拟方法模拟了单根P菌毛在应变作用下的伸长和收缩特性。该模拟模型基于在外力作用下变形的三态能量景观。键的张开和闭合用Bells理论来描述，而毛状线性化部分的伸长用蠕虫链模型来描述。将模拟结果与测力光钳的测量结果进行了比较。结果表明，在平衡和动态条件下，包括熵效应在内，模拟都能再现菌毛的伸长和回缩。结果表明，模拟可以评估各种模型参数，如展开力、势垒高度和能量格局中的各种距离，包括它们的随机扩散，而分析模型无法做到这一点。结果表明，MC模拟对模拟P菌毛的伸长和回缩特性是有用的，因此可能也适用于其他类型的菌毛，暴露在应变和/或应力下。MC模拟特别适合描述螺旋状菌毛，因为它们具有复杂的自我调节的机械伸长行为，这使得当研究动态过程时，或者如果需要对杆中的额外相互作用或粘连尖端的行为进行建模时，分析描述不是微不足道的。
P pili are fimbrial adhesion organelles expressed by uropathogenic Escherichia coli in the upper urinary tract. They constitute a stiff helix-like polymer consisting of a number of subunits joined by head-to-tail bonds. The elongation and retraction properties of individual P pili exposed to strain have been modeled by Monte Carlo (MC) simulations. The simulation model is based upon a three-state energy landscape that deforms under an applied force. Bond opening and closure are modeled by Bells theory while the elongation of the linearized part of the pilus is described by a worm-like chain model. The simulations are compared with measurements made by force measuring optical tweezers. It was found that the simulations can reproduce pili elongation as well as retraction, under both equilibrium and dynamic conditions, including entropic effects. It is shown that the simulations allow for an assessment of various model parameters, e.g. the unfolding force, energy barrier heights, and various distances in the energy landscape, including their stochastic spread that analytical models are unable to do. The results demonstrate that MC simulations are useful to model elongation and retraction properties of P pili, and therefore presumably also other types of pili, exposed to strain and/or stress. MC simulations are particularly suited for description of helix-like pili since these have an intricate self-regulating mechanical elongation behavior that makes analytical descriptions non-trivial when dynamic processes are studied, or if additional interactions in the rod or the behavior of the adhesion tip needs to be modeled.