Properties of Microtubules with Isotropic and Anisotropic Mechanics

Microtubules (MTs) are intrinsic components of the cytoskeleton, and their mechanical properties are key for many of their functions in the cell. Here we present a coarse-grained model of a MT where we can explicitly control the mechanical properties and thus can explore the relative contributions of geometry and anisotropy. We begin with the isotropic mechanics case and then investigate various forms of anisotropic mechanics where we systematically vary the axial, circumferential and shear moduli. We find that the axial Young's modulus is always the dominant factor in determining the persistence length, but the shear modulus is also a strong contributing factor for MTs less than a few microns in length. In the case of anisotropic mechanics, we find that MTs of different lengths have consistent mechanical properties, but the persistence length only depends on the MT segment length that is considered and not the overall length of the MT. Further, for MTs more than a few microns in length, anisotropic effects are only apparent in the higher-order fluctuations and thus would be difficult to detect in experiments.