Chetrit Einat, Sharma Sabita, Maayan Uri, Pelah Maya Georgia, Klausner Ziv, Popa Ionel, Berkovich Ronen
Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 8410501, Israel.
Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI, 53211, USA.
Curr Res Struct Biol. 2022 Apr 28;4:106-117. doi: 10.1016/j.crstbi.2022.04.003. eCollection 2022.
While performing under mechanical loads , polyproteins are vitally involved in cellular mechanisms such as regulation of tissue elasticity and mechano-transduction by unfolding their comprising domains and extending them. It is widely thought that the process of sequential unfolding of polyproteins follows an exponential kinetics as the individual unfolding events exhibit identical and identically distributed (iid) Poisson behavior. However, it was shown that under high loads, the sequential unfolding kinetics displays nonexponential kinetics that alludes to aging by a subdiffusion process. Statistical order analysis of this kinetics indicated that the individual unfolding events are not iid, and cannot be defined as a Poisson (memoryless) process. Based on numerical simulations it was argued that this behavior becomes less pronounced with lowering the load, therefore it is to be expected that polyproteins unfolding under lower forces will follow a Poisson behavior. This expectation serves as the motivation of the current study, in which we investigate the effect of force lowering on the unfolding kinetics of Poly-L under varying loads, specifically high (150, 100 pN) and moderate-low (45, 30, 20 pN) forces. We found that a hierarchy among the unfolding events still exists even under low loads, again resulting in nonexponential behavior. We observe that analyzing the dwell-time distributions with stretched-exponentials and power laws give rise to different phenomenological trends. Using statistical order analysis, we demonstrated that even under the lowest load, the sequential unfolding cannot be considered as iid, in accord with the power law distribution. Additional free energy analysis revealed the contribution of the unfolded segments elasticity that scales with the force on the overall one-dimensional contour of the energy landscape, but more importantly, it discloses the hierarchy within the activation barriers during sequential unfolding that account for the observed nonexponentiality.
在承受机械负荷时,多聚蛋白通过展开其组成结构域并使其伸展,在细胞机制中发挥着至关重要的作用,如调节组织弹性和机械转导。人们普遍认为,多聚蛋白的顺序展开过程遵循指数动力学,因为各个展开事件表现出相同且独立同分布(iid)的泊松行为。然而,研究表明,在高负荷下,顺序展开动力学呈现非指数动力学,这暗示了通过亚扩散过程导致的老化。对这种动力学的统计阶次分析表明,各个展开事件并非iid,且不能定义为泊松(无记忆)过程。基于数值模拟,有人认为随着负荷降低,这种行为会变得不那么明显,因此可以预期在较低力作用下多聚蛋白的展开将遵循泊松行为。这一预期成为本研究的动机,在本研究中,我们研究了力降低对不同负荷下(特别是高负荷:150、100 pN,以及中低负荷:45、30、20 pN)聚-L展开动力学的影响。我们发现,即使在低负荷下,展开事件之间的层次结构仍然存在,再次导致非指数行为。我们观察到,用拉伸指数和幂律分析驻留时间分布会产生不同的现象学趋势。使用统计阶次分析,我们证明即使在最低负荷下,顺序展开也不能被视为iid,这与幂律分布一致。额外的自由能分析揭示了展开片段弹性的贡献,其与能量景观的整体一维轮廓上的力成比例,但更重要的是,它揭示了顺序展开过程中激活屏障内的层次结构,这解释了观察到的非指数性。