Biology subjects

Bieling, P.

Publications and source records attributed to Bieling, P..

2 recordsLinked to original sources

bioRxiv2019

Profilin and formin constitute a pacemaker system for robust actin filament growth

The actin cytoskeleton drives many essential biological processes, from cell morphogenesis to motility. Assembly of functional actin networks requires control over the speed at which actin filaments grow. How this can be achieved at the high and variable levels of soluble actin subunits found in cells is unclear. Here we reconstitute assembly of mammalian, non-muscle actin filaments from physiological concentrations of profilin-actin. We discover that under these conditions, filament growth is limited by profilin dissociating from the filament end and the speed of elongation becomes insensitive to the concentration of soluble subunits. Profilin release can be directly promoted by formin actin polymerases even at saturating profilin-actin concentrations. We demonstrate that mammalian cells indeed operate at the limit to actin filament growth imposed by profilin and formins. Our results reveal how synergy between profilin and formins generates robust filament growth rates that are resilient to changes in the soluble subunit concentration.

biochemistry↗

bioRxiv2019

Extraction of active RhoGTPases by RhoGDI regulates spatiotemporal patterning of RhoGTPases

The RhoGTPases are characterized as membrane-associated molecular switches cycling between active, GTP-bound and inactive, GDP-bound states. However, 90-95% of RhoGTPases are maintained in a soluble form by RhoGDI, which is generally viewed as a passive shuttle for inactive RhoGTPases. Our current understanding of RhoGTPase:RhoGDI dynamics has been limited by two experimental challenges: direct visualization of the RhoGTPases in vivo and reconstitution of the cycle in vitro. We developed methods to directly image vertebrate RhoGTPases in vivo or on lipid bilayers in vitro. Using these tools, we identified pools of active and inactive RhoGTPase associated with the membrane, showed that RhoGDI can actively extract both inactive and active RhoGTPases, and that the extraction of active RhoGTPase contributes to their spatial regulation around wounds. In contrast to the textbook model of the RhoGTPase cycle, these results indicate that RhoGDI actively contributes to spatiotemporal patterning by removing active RhoGTPases from the plasma membrane.

cell biology↗