Booth EA, Sterling SM, Dovala D, Nogales E, Thorner J

Septins are a protein family found in all eukaryotes (except higher plants) that have roles in membrane remodeling, formation of diffusion barriers, and as a scaffold to recruit other proteins. In budding yeast, proper execution of cytokinesis and cell division requires formation of a collar of circumferential filaments at the ...

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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 Foerster 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 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 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.

Date: Oct. 30, 2016

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