Evolutionary tuning of barbed end competition allows simultaneous construction of architecturally distinct actin structures

How cells simultaneously assemble actin structures of distinct sizes, shapes, and filamentous architectures is still not well understood. Here, we used budding yeast as a model to investigate how competition for the barbed ends of actin filaments might influence this process. We found that while vertebrate capping protein (CapZ) and formins can simultaneously associate with barbed ends and catalyze each other's displacement, yeast capping protein (Cap1/2) poorly displaces both yeast and vertebrate formins. Consistent with these biochemical differences, in vivo formin-mediated actin cable assembly was strongly attenuated by the overexpression of CapZ but not Cap1/2. Multiwavelength live cell imaging further revealed that actin patches in cap2 increment cells acquire cable-like features over time, including recruitment of formins and tropomyosin. Together, our results suggest that the activities of S. cerevisiae Cap1/2 have been tuned across evolution to allow robust cable assembly by formins in the presence of high cytosolic levels of Cap1/2, which conversely limit patch growth and shield patches from formins. Competition at barbed ends between capping proteins and formins leads to the assembly of architecturally distinct cellular actin structures and the differential sorting of actin-binding proteins to each structure.

Automated summary

This study investigated how cells assemble actin structures of different sizes, shapes, and filamentous architectures. The researchers found that yeast capping protein (Cap1/2) poorly displaces formins, while vertebrate capping protein (CapZ) can simultaneously associate with formins. Overexpression of CapZ strongly attenuated formin-mediated actin cable assembly, while overexpression of Cap1/2 did not have the same effect. Furthermore, live cell imaging showed that actin patches in cap2 increment cells acquired cable-like features over time.