Binding of PI4,5P2 by septin complexes is required for their essential function in cytokinesis in budding yeast

Abstract

Septins comprise a conserved family of proteins that are involved in processes of membrane remodeling, such as cytokinesis. Cytokinesis in budding yeast (Saccharomyces cerevisiae) requires assembly of septins adjacent to the plasma membrane of the mother‐bud neck, where they serve as a protein scaffold and diffusion barrier. The aim of our studies is to determine how septins are recruited to and anchored at the plasma membrane. Among plasma membrane constituents, phosphatidylinositol‐4,5‐bisphosphate (PI4,5P2) is a potential candidate for recruiting septins, because at the site of cytokinesis, the plasma membrane in mammalian cells is enriched in PI4,5P2, which is required for cytokinesis [Emoto et al. (2005) J. Biol. Chem. 280: 37901]. PI4,5P2 is also required for proper septin localization in yeast [Rodríguez‐Escudero et al. (2005) Biochem. J. 390: 613]. Our work indicates that a PI4,5P2‐binding reporter localizes preferentially to the yeast bud neck. In addition, liposome flotation assays show that the yeast septins Cdc3, Cdc11 and Cdc12 bind to PI4,5P2‐containing vesicles in vitro. Furthermore, complexes of Cdc3, Cdc10, Cdc11 and Cdc12 also bind PI4,5P2. Mutation of basic residues in Cdc3 decreases PI4,5P2 binding in vitro and causes defects in cytokinesis in vivo, supporting the view that septin‐PI4,5P2 interaction is required for the septins to execute their function in cytokinesis. NIH R01 GM21841