Growth and shortening of microtubules: a two-state model approach

TL;DR

This paper presents a two-state mechanochemical model for microtubule dynamics, capturing growth and shrinkage processes influenced by external forces and GTP-tubulin concentration, with parameters fitted to experimental data.

Contribution

The study introduces a novel two-state model for microtubule instability that incorporates force-dependent switching and detailed mechanochemical processes.

Findings

Microtubules are mainly in the assembly state.

Mean growth velocity increases with external force and GTP-tubulin concentration.

Microtubules tend to shorten on average without external force.

Abstract

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.