FREE ENERGY CONVERSION IN BIOLOGY

这是去年关于运动机制的工作的延续 运动蛋白在微管(一种周期性生物聚合物)上的表达 由相同的单体亚基制成)。当单个动蛋白分子 附着在微型塑料珠子上的可以自行移动并携带 通过催化它在微管上单向地将其包裹在一起 三磷酸腺苷的水解。这场运动可以由两个人单头进行 和两个头的动蛋白分子。在双头情况下，最简单的 运动机制是所谓的“双手交接”模型，在这种模型中， 两个磁头在附加和分离状态之间交替 有序的序列(就像一个人走路的动作)。一点儿没错 目前还不清楚单头动蛋白是如何移动珠子的。我们在中国的研究 今年的重点是这个问题。我们的研究得出了两个结论 调查结果。第一，用跨越桥梁的形式主义理论 肌肉收缩时，我们发现珠子在一个 由单个单头运动蛋白驱动的微管相当于 布朗粒子在起伏周期势中的运动 菲尔德。因此，理解心绞痛发病机制的第一步 动蛋白运动就是为了解决布朗运动问题。这场运动 布朗粒子在起伏的周期势场中存在 以前对于每个周期内的势的情况都得到了解决 是不对称的。对于生物马达来说，电势是对称的。不是 关于对称势的这类研究已经被报道到 现在。我们是第一个解决这个问题的人。我们已经发现，在 布朗粒子在空间中执行偏向运动的命令 涨落周期对称势，满足以下两个条件 必须得到满足。首先，势能必须在三者之间波动。 或者更平移的“势态”。第二， 波动过程必须以这样一种方式进行，即一个净循环 这些状态是存在的。使用我们开发的模型，我们发现单个 单头动蛋白确实可以移动微管上的珠子，如果 激动素可以以两种不同的构象附着在微管上 相对于微管的轴线具有不同的倾斜角。 我们还发展了一种计算运动速度的公式 粒子在长时间内的运动参数 给出了波动过程。形式主义应该在 以微珠为动力的体外运动测量研究 单头动蛋白分子。

This is a continuation of last year's work on the mechanisms of movement of the motor protein kinesin on a microtubule (a periodic biopolymer made of identical monomer subunits). A single kinesin molecule when attached to a microscopic plastic bead can move itself and carry the bead with it unidirectionally on a microtubule by catalyzing the hydrolysis of ATP. The movement can be carried out by both one-headed and two-headed kinesin molecules. In the two-headed case, the simplest mechanism for movement is the so-called "hand-over-hand" model, in which the two heads alternate between attached and detached states in an ordered sequence (like the walking motion of a human being). Exactly how a one-headed kinesin moves the bead is not clear. Our research in this year was centered on this question. Our research has yielded two findings. First, using the theory of "cross-bridge" formalism for muscle contraction, we have found that the movement of a bead on a microtubule powered by a single one-headed kinesin is equivalent to the movement of a Brownian particle in a fluctuating periodic potential field. Therefore, the first step in understanding the mechanism of kinesin movement is to solve the Brownian motion problem. The movement of a Brownian particle in a fluctuating periodic potential field has been solved before for the case that the potential within each period is asymmetric. For biological motors, the potential is symmetric. No studies of this kind on symmetric potentials have been reported up to now. We are the first to solve this problem. We have found that, in order for a Brownian particle to execute a biased movement in a fluctuating periodic symmetric potential, the following two conditions have to be satisfied. First, the potential must fluctuate among three or more translationally-shifted "potential states". Second, the fluctuation process must be done in such a way that a net cycling around the states exists. Using the model we developed, we found that a single one-headed kinesin indeed can move a bead on a microtubule if the kinesin can attached to the microtubule in two distinct conformations with different tilting angles relative to the axis of the microtubule. We also have developed a formalism for calculating the movement velocity of the particle at long time when the kinetic parameters of the fluctuation process are given. The formalism should be useful in studying in vitro motility measurements in which the bead is powered by one-headed kinesin molecules.