Turnover in active membranes

In contrast to extensile active stresses that generate continuous defect-driven turbulence, contractile active stresses in reconstituted cytoskeletal systems cause an irreversible collapse in size. In living systems, contractile mechanisms are regulated by the turnover of molecular components. However, reconstituting such dynamics in vitro has proven challenging. Here, we study how active stresses couple with the local turnover of the molecular components. We demonstrate that tip-adhering kinesin-4 motors drive the formation of macroscopic one-microtubule thick monolayer membranes. These membranes exhibit pronounced and continuous height deformations. Surprisingly, once a growing local deformation reaches a critical height, it rapidly relaxes. Analysis of continuum fields suggests that the relaxation of the local height protrusion is coupled to the disassembly of microtubules. Our work demonstrates a system of active membranes whose fluctuations are regulated by the disassembly and continuous turnover of microscopic components. These structural motifs can be organized into bulk materials that exhibit novel structural and mechanical properties.