一种生长中的吸附多形丝的动力学不稳定性
Dynamic instability of a growing adsorbed polymorphic filament
摘要：
聚合物组装体中缓慢生长和快速收缩之间的间歇性转变被称为动态不稳定性，这是在包括微管、肌动蛋白及其细菌类似物在内的各种生物化学上不同的组装体中观察到的特征。这种聚合物的不稳定相的存在在细胞骨架动力学中具有许多功能性后果，并且其重复出现表明它相对容易进化。在这里，我们认为存在的动态不稳定性的最小成分，通过考虑一个单一的多态性的长丝，通过结合到一个基板，经历了构象变化，并可能解绑作为结果的残余应变引起的这种变化。我们确定了两个参数，控制相空间的可能性的细丝：一个结构的机械参数，其特征在于沿细丝的键强度的比率与基板（或相当于在组装的纵向横向相互作用的比率），和动力学参数，其特征在于生长和构象变化的时间尺度的比率。在确定性极限中，这些参数用来区分不间断增长的区域和崩溃的区域。然而，在结构或动力学参数中存在无序的情况下，生长和塌陷阶段可以共存，其中细丝可以缓慢生长，快速收缩，并且在这些阶段之间过渡，从而表现出动态不稳定性。我们展示了动态不稳定的相图，使我们能够量化这个不稳定的阶段的演化存在的窗口。
英文摘要：
The intermittent transition between slow growth and rapid shrinkage in polymeric assemblies is termed dynamic instability, a feature observed in a variety of biochemically distinct assemblies including microtubules, actin and their bacterial analogs. The existence of this labile phase of a polymer has many functional consequences in cytoskeletal dynamics, and its repeated appearance suggests that it is relatively easy to evolve. Here, we consider the minimal ingredients for the existence of dynamic instability by considering a single polymorphic filament that grows by binding to a substrate, undergoes a conformation change, and may unbind as a consequence of the residual strains induced by this change. We identify two parameters that control the phase space of possibilities for the filament: a structural mechanical parameter that characterizes the ratio of the bond strengths along the filament to those with the substrate (or equivalently the ratio of longitudinal to lateral interactions in an assembly), and a kinetic parameter that characterizes the ratio of time scales for growth and conformation change. In the deterministic limit, these parameters serve to demarcate a region of uninterrupted growth from that of collapse. However, in the presence of disorder in either the structural or the kinetic parameter the growth and collapse phases can coexist where the filament can grow slowly, shrink rapidly, and transition between these phases, thus exhibiting dynamic instability. We exhibit the window for the existence of dynamic instability in a phase diagram that allows us to quantify the evolvability of this labile phase.
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