An active biopolymer network controlled by molecular motors

TLDR

The study presents an active polymer network where processive molecular motors control elasticity, proposing that this design principle could inspire active materials that self‑adjust stiffness via internal catalytic control. The network comprises actin filaments cross‑linked by filamin A and contracted by bipolar muscle myosin II filaments, with myosin motors stiffening the network over two orders of magnitude by pulling on FLNa‑anchored actin and generating internal stress. The network’s stiffening response closely mimics external shear, with internal and external stresses driving it into a highly nonlinear, stiffened regime; the active stress reaches ~14 Pa, matching a 1‑pN force per myosin head, and the behavior parallels cellular mechanics, implying that adherent cells may regulate stiffness by operating in a nonlinear regime sensitive to motor activity.

Abstract

We describe an active polymer network in which processive molecular motors control network elasticity. This system consists of actin filaments cross-linked by filamin A (FLNa) and contracted by bipolar filaments of muscle myosin II. The myosin motors stiffen the network by more than two orders of magnitude by pulling on actin filaments anchored in the network by FLNa cross-links, thereby generating internal stress. The stiffening response closely mimics the effects of external stress applied by mechanical shear. Both internal and external stresses can drive the network into a highly nonlinear, stiffened regime. The active stress reaches values that are equivalent to an external stress of 14 Pa, consistent with a 1-pN force per myosin head. This active network mimics many mechanical properties of cells and suggests that adherent cells exert mechanical control by operating in a nonlinear regime where cell stiffness is sensitive to changes in motor activity. This design principle may be applicable to engineering novel biologically inspired, active materials that adjust their own stiffness by internal catalytic control.