Binding dynamics of alpha-actinin-4 in dependence of actin cortex tension

Abstract

Mechano-sensation of cells is an important prerequisite for cellular function, e.g. in the context of cell migration, tissue organisation and morphogenesis. An important mechano-chemical-transducer is the actin cytoskeleton. In fact, previous studies have shown that actin cross-linkers, such as α-actinin-4, exhibit mechanosensitive properties in its binding dynamics to actin polymers. However, to date, a quantitative analysis of tension-dependent binding dynamics in live cells is lacking. Here, we present a new technique that allows to quantitatively characterize the dependence of cross-linking lifetime of actin cross-linkers on mechanical tension in the actin cortex of live cells. We use an approach that combines parallel plate confinement of round cells, fluorescence recovery after photo-bleaching, and a mathematical mean-field model of cross-linker binding. We apply our approach to the actin cross-linker α-actinin-4 and show that the cross-linking time of α-actinin-4 homodimers increases approximately twofold within the cellular range of cortical mechanical tension rendering α-actinin-4 a catch bond in physiological tension ranges.

Distinct forms of the actin cross-linking protein α-actinin support macropinosome internalization and trafficking

“…Additionally, previous research has indicated that α-actinin 4 acts as a mechanosensitive actinbinding protein through its catch-slip activity which allows it to bind or release actin based on mechanical tension. This could potentially explain why we observe α-actinin 4 is more important for the dynamic actin remodeling in membrane ruffles (Xu et al, 1998;Fukumoto et al, 2015;Hosseini et al, 2020). In addition, while we were interested in trafficking of macropinosomes to the lysosome as that provides nutrients to the proliferating tumor cells, the actinin proteins may also regulate recycling of material from macropinosomes back to the plasma membrane via interactions with other actin nucleating machinery such as WASH.…”

On the role of mechanosensitive binding dynamics in the pattern formation of active surfaces

“…Motivated by experimental observations, see e.g. [21][22][23][24] , we anticipate that the unbinding rate of molecular regulators of active stress depends on the local trace of the in-plane stress t i i . In particular, we make the choice of a Bell model dependence…”

“…Some actin cross-linkers such as α-actinin-4 and myosin have been shown to exhibit a catch-bond behavior 21,23,37 .…”

“…Furthermore, the degree of cross-linking of actin networks was shown to sensitively tune the network's mechanical resistance towards shear deformations 18,19 . In recent years, several experimental studies have provided direct or indirect evidence that actin cross-linkers exhibit mechanosensitive binding dynamics [20][21][22][23][24][25] . In particular, two scenarios have been suggested for cross-linker binding to actin 23,24 ; i) tension-induced increase of bond lifetimes -also called catch bond behavior and ii) tension-induced decrease of bond lifetimes -also called slip bond behavior.…”

“…In recent years, several experimental studies have provided direct or indirect evidence that actin cross-linkers exhibit mechanosensitive binding dynamics [20][21][22][23][24][25] . In particular, two scenarios have been suggested for cross-linker binding to actin 23,24 ; i) tension-induced increase of bond lifetimes -also called catch bond behavior and ii) tension-induced decrease of bond lifetimes -also called slip bond behavior. Therefore, in a cortex model that captures mechanosensitivity of stress-regulating cortical molecules, the unbinding rate of such molecules needs to depend on the local mechanical stress in the cortical surface.…”