This year's final lecture focuses on the second aspect of cellular tension, namely cortical tension. It emerges from the contractile activity of Myosin-like molecular motors, associating with the actin filaments of the cellular cortex.
We begin by describing the remarkable properties of Myosin motors, complex mechanoenzymes that follow an ATP-driven kinetic cycle by utilizing the free energy of ATP binding and hydrolysis, and the dissociation of the hydrolysis products, inorganic phosphate and ADP. The kinetic regulation of Myosins determines the motor duty cycle, a measure of the fraction of the cycle associated with the generation of mechanical force. Mechanisms for adjusting this variable are developed, with particular emphasis on the role of biochemical regulation of Myosin-II, and that of mechanical forces.
The second part of the lecture then turns to the central question of the emergence of tension forces in a network driven by Myosin-II contractile forces. The joint contributions of actin cross-linkers, Myosin-II activity, its organization into minifilaments, and the length and spatial organization of actin filaments are assessed in the light of recent studies combining measurement of physico-chemical parameters, perturbations and modeling.
