Department of Biomedical Engineering, Duke University, Durham, North Carolina.
Department of Biomedical Engineering, Duke University, Durham, North Carolina; Department of Cell Biology, Duke University, Durham, North Carolina.
Biophys J. 2020 Aug 18;119(4):792-805. doi: 10.1016/j.bpj.2020.05.041. Epub 2020 Jul 17.
Bacterial cell division is tightly coupled to the dynamic behavior of FtsZ, a tubulin homolog. Recent experimental work in vitro and in vivo has attributed FtsZ's assembly dynamics to treadmilling, in which subunits add to the bottom and dissociate from the top of protofilaments. However, the molecular mechanisms producing treadmilling have yet to be characterized and quantified. We have developed a Monte Carlo model for FtsZ assembly that explains treadmilling, and also explains assembly nucleation by the same mechanisms. A key element of the model is a conformational change from R (relaxed), which is highly favored for monomers, to T (tense), which is favored for subunits in a protofilament. This model was created in MATLAB. Kinetic parameters were converted to probabilities of execution during a single, small time step. These were used to stochastically determine FtsZ dynamics. Our model is able to accurately describe the results of several in vitro and in vivo studies for a variety of FtsZ flavors. With standard conditions, the model FtsZ polymerized and produced protofilaments that treadmilled at 23 nm/s, hydrolyzed GTP at 3.6-3.7 GTP min FtsZ, and had an average length of 30-40 subunits, all similar to experimental results. Adding a bottom capper resulted in shorter protofilaments and higher GTPase, similar to the effect of the known bottom capper protein MciZ. The model could match nucleation kinetics of several flavors of FtsZ using the same parameters as treadmilling and varying only the R to T transition of monomers.
细菌细胞分裂与 FtsZ 的动态行为紧密相关，FtsZ 是一种微管蛋白同系物。最近的体外和体内实验工作将 FtsZ 的组装动力学归因于 treadmilling，即在原纤维的底部添加亚基并从顶部解离。然而，产生 treadmilling 的分子机制尚未得到表征和量化。我们开发了一个用于 FtsZ 组装的蒙特卡罗模型，该模型解释了 treadmilling，并且还通过相同的机制解释了组装成核。该模型的一个关键要素是从 R（松弛）到 T（紧张）的构象变化，对于单体来说，R 是高度有利的，而对于原纤维中的亚基来说，T 是有利的。该模型是在 MATLAB 中创建的。动力学参数转换为在单个小时间步内执行的概率。这些用于随机确定 FtsZ 动力学。我们的模型能够准确描述各种 FtsZ 变体的几种体外和体内研究的结果。在标准条件下，模型 FtsZ 聚合并产生以 23nm/s 进行 treadmilling 的原纤维，以 3.6-3.7GTP min FtsZ 的速度水解 GTP，并具有 30-40 个亚基的平均长度，所有这些都与实验结果相似。添加底部盖帽会导致原纤维变短和 GTPase 增加，类似于已知的底部盖帽蛋白 MciZ 的作用。该模型可以使用与 treadmilling 相同的参数并仅改变单体的 R 到 T 的转变来匹配几种 FtsZ 变体的成核动力学。
