Molecular Mechanics of Cells and Tissues

Abstract

In this review I address the question: can we understand the mechanics of organelles and cells based on the material properties and spatial arrangements of the cytoskeletal molecules such as microtubules, actin filaments and the host of associated proteins that crosslink them? In other words, can we do a structural analysis of a cell, as a mechanical engineer would perform a structural analysis on the design of a building or a bridge? This question can now be addressed because mechanical properties, such as stiffness and flexural rigidity, have been measured for several cytoskeletal proteins using single-molecule techniques. Owing to their small size, individual filaments are very soft and are readily bent by thermal and motor-driven forces. Strength can be increased by crosslinking. Crosslinked bundles are a first step in a hierarchy of structures formed with filaments. Recent work has clarified how the rigidity of crosslinked bundles varies with the length and the number of constituent filaments. From these considerations comes an appreciation for how the material properties of the cytoskeleton impose mechanical limitations on the design of organelles such as axonemes and hair bundles. The combination of theory and experiment promises to put cellular biomechanics on a firm molecular foundation.