Nematode sperm motility: nonpolar filament polymerization mediated by end-tracking motors.
Nematode sperm motility: nonpolar filament polymerization mediated by end-tracking motors.
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DOI：
10.1529/biophysj.106.090472
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发表时间：
2007-01
影响因子：
3.4
通讯作者：
R. Dickinson;D. Purich
中科院分区：
文献类型：
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作者：
R. Dickinson;D. Purich
在线虫精子细胞的运动中，主要精子蛋白(MSP)的细丝组装导致动态的膜突起，其方式与其他真核细胞中基于肌动蛋白的运动非常相似。矛盾的是，基于肌动蛋白的运动是通过将ATP结合的肌动蛋白亚单位添加到位于细胞膜上的肌动蛋白细丝+端来驱动的，而MSP二聚体从溶液中组装成缺乏核苷酸结合位点的非极性微丝。因此，细丝的极性和细丝上的ATP水解，尽管对基于肌动蛋白的运动性是必不可少的，但对于MSP的膜突起似乎是不必要的。作为这一悖论的潜在解决方案，我们提出了一个MSP细丝末端跟踪蛋白组装MSP细丝和力产生的模型。在这个模型中，ATP水解驱动膜相关蛋白和细丝末端之间亲和力调节的、过程性的相互作用。然而，与肌动蛋白细丝末端跟踪马达的“动作夹紧”模型相反，ATP激活跟踪蛋白(或可溶性辅助因子)，而不是MSP亚基本身(与通过ATP结合激活肌动蛋白亚基相反)。MSP末端跟踪模型预测的性质与基于MSP的运动性的几个关键观察结果一致，包括持久的膜附着、膜上丝端的聚合和游离丝端的解聚，以及聚合速度与非MSP可溶细胞质成分浓度的饱和依赖关系。
In nematode sperm cell motility, major sperm protein (MSP) filament assembly results in dynamic membrane protrusions in a manner that closely resembles actin-based motility in other eukaryotic cells. Paradoxically, whereas actin-based motility is driven by addition of ATP-bound actin subunits onto actin filament plus-ends located at the cell membrane, MSP dimers assemble from solution into nonpolar filaments that lack a nucleotide binding site. Thus, filament polarity and on-filament ATP hydrolysis, although essential for actin-based motility, appear to be unnecessary for membrane protrusions by MSP. As a potential resolution to this paradox, we propose a model for MSP filament assembly and force generation by MSP filament end-tracking proteins. In this model, ATP hydrolysis drives affinity-modulated, processive interactions between membrane-associated proteins and elongating filament ends. However, in contrast to the "actoclampin" model for actin filament end-tracking motors, ATP activates the tracking protein (or a soluble cofactor) rather than the MSP subunits themselves (in contrast to activation of actin subunits by ATP binding). The MSP end-tracking model predicts properties that are consistent with several key observations of MSP-based motility, including persistent membrane attachment, polymerization of filament ends at the membrane with depolymerization of free-filament ends away from the membrane, as well as a saturating dependence of polymerization rate on the concentration of non-MSP soluble cytoplasmic components.