Authors
Sun, J., Nanyang Technological University
Han, X., Nanyang Technological University
Gao, Y., Nanyang Technological University
Miao, Y., Nanyang Technological University
Polarized fungal growth requires the highly-coordinated assembly of actin cable aligning along the mother-daughter axis. For directional actin polymerization during polarized growth, actin cable nucleator formin and formin nucleation promoting factors maintain a condensed-zone at the bud tip. A macromolecular complex called polarisome plays essential roles in regulating these actin-binding proteins in a spatial-temporal manner throughout the cell cycle progression. However, the protein constituents in the polarisome and their intra- or inter-molecular interactions for the dynamic regulation of protein functions in actin assembly and polarized cell growth remain elusive. Recently, we have identified a previously uncharacterized actin-interacting protein 5 (Aip5), which directly interacts with formin and Spa2, the scaffolder of the polarisome complex. Through the cell biology, biochemical, and structural biology studies, we have revealed that by interacting with formin, Aip5, independently or synergistically nucleates actin filament assembly. Furthermore, using both in vivo cell imaging and in vitro protein reconstitution experiments, we found that the intrinsically disordered region of Aip5 plays essential roles in regulating the protein function through phase separation mechanism, in a Spa2- and actin-dependent manner, during stress adaptation. The macromolecular condensation of Aip5 provides a few new mechanisms underlying the regulation of actin polymerization during polarized fungal growth or stress adaptation.
