In this study, a two-state mechanochemical model is presented to describe the dynamic instability of microtubules (MTs) in cells. The MTs switches between two states, assembly state and disassembly state. In assembly state, the growth of MTs includes two processes: free GTP-tubulin binding to the tip of protofilament (PF) and conformation change of PF, during which the first tubulin unit which curls outwards is rearranged into MT surface using the energy released from the hydrolysis of GTP in the penultimate tubulin unit. In disassembly state, the shortening of MTs includes also two processes, the release of GDP-tibulin from the tip of PF and one new tubulin unit curls out of the MT surface. Switches between these two states, which are usually called rescue and catastrophe, happen stochastically with external force dependent rates. Using this two-state model with parameters obtained by fitting the recent experimental data, detailed properties of MT growth are obtained, we find that MT is mainly in assembly state, its mean growth velocity increases with external force and GTP-tubulin concentration, MT will shorten in average without external force. To know more about the external force and GTP-tubulin concentration dependent properties of MT growth, and for the sake of the future experimental verification of this two-state model, eleven {\it critical forces} are defined and numerically discussed.
Beyond the tip: Lattice dynamics, seams, and the mechanism of microtubule fracture
Université Grenoble-Alpes（格勒诺布尔阿尔卑斯大学）；CNRS, Laboratoire Interdisciplinaire de Physique（法国国家科学研究中心，交叉物理实验室）；Saarland University（萨尔兰大学）；Experimental Physics and Center for Biophysics, Saarland University（萨尔兰大学实验物理与生物物理中心）；PharmaScienceHub (PSH)（制药科学枢纽）
