Effects of Bni5 Binding on Septin Filament Organization.
Septins are a protein family found in all eukaryotes (except higher plants) that have roles in membrane remodeling and formation of diffusion barriers and as a scaffold to recruit other proteins. In budding yeast, proper execution of cytokinesis and cell division requires the formation of a collar of circumferential filaments at the bud neck. These filaments are assembled from apolar septin hetero-octamers. Currently, little is known about the mechanisms that control the arrangement and dynamics of septin structures. In this study, we utilized both Förster resonance energy transfer and electron microscopy to analyze the biophysical properties of the septin-binding protein Bni5 and how its association with septin filaments affects their organization. We found that the interaction of Bni5 with the terminal subunit (Cdc11) at the junctions between adjacent hetero-octamers in paired filaments is highly cooperative. Both the C-terminal end of Bni5 and the C-terminal extension of Cdc11 make important contributions to their interaction. Moreover, this binding may stabilize the dimerization of Bni5, which, in turn, forms cross-filament braces that significantly narrow, and impose much more uniform spacing on, the gap between paired filaments.
Division of Biochemistry, Biophysics, and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA. Electronic address: elizabeth.booth@Grifols.com.
Elizabeth A
EA
Booth
Division of Biochemistry, Biophysics, and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA. Electronic address: smsterling@berkeley.edu.
Sarah M
SM
Sterling
Program in Microbial Pathogenesis and Host Defense, Department of Microbiology and Immunology, University of California School of Medicine, San Francisco, CA 94143, USA. Electronic address: dustin.dovala@novartis.com.
Dustin
D
Dovala
Division of Biochemistry, Biophysics, and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA; Life Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA. Electronic address: ENogales@lbl.gov.
Eva
E
Nogales
Division of Biochemistry, Biophysics, and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3202, USA. Electronic address: jthorner@berkeley.edu.
Jeremy
J
Thorner
D031541:Fluorescence Resonance Energy Transfer; D008854:Microscopy, Electron; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D011485:Protein Binding; D025941:Protein Interaction Mapping; D055503:Protein Multimerization; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D058112:Septins / Q000378:metabolism*
C466084:BNI5 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D058112:Septins
FRET analysis; analytical ultracentrifugation; electron microscopy; field-flow fractionation; yeast (Saccharomyces cerevisiae)