Xie, Y., Sun, J., Han, X. et al. Polarisome scaffolder Spa2-mediated macromolecular condensation of Aip5 for actin polymerization. Nat Commun 10, 5078 (2019). https://doi.org/10.1038/s41467-019-13125-1
A multiprotein complex polarisome nucleates actin cables for polarized cell growth in budding yeast and filamentous fungi. However, the dynamic regulations of polarisome proteins in polymerizing actin under physiological and stress conditions remains unknown. We identify a previously functionally unknown polarisome member, actin-interacting-protein 5 (Aip5), which promotes actin assembly synergistically with formin Bni1. Aip5-C terminus is responsible for its activities by interacting with G-actin and Bni1. Through N-terminal intrinsically disordered region, Aip5 forms high-order oligomers and generate cytoplasmic condensates under the stresses conditions. The molecular dynamics and reversibility of Aip5 condensates are regulated by scaffolding protein Spa2 via liquid-liquid phase separation both in vitro and in vivo. In the absence of Spa2, Aip5 condensates hamper cell growth and actin cable structures under stress treatment. The present study reveals the mechanisms of actin assembly for polarity establishment and the adaptation in stress conditions to protect actin assembly by protein phase separation.
We are grateful to Daniela Rhodes, Yasunori Saheki, and David Drubin for critical reading of the manuscript. We thank Jackie Tan for helping with the TEM work. We thank Min Wu (NUS, Singapore) for sharing the Nikon imaging system for TIRF microscopy. We thank David Drubin for sharing the strains. We also thank the NTU Protein Production Platform (www.proteins.sg) for protein expression test and purification of Spa2-C. This study was supported by NTU start-up grant (M4081533), MOE Tier 2 (MOE2016-T2-1-005S), Tier 1 (RG38/17-S), SRIS (SIG18002/M4062479) to Y.M., and MOE Tier 2 (MOE2015-T2-1-078) to Y.-G.G. in Singapore.