BAR scaffolds drive membrane fission by crowding disordered domains

Wilton T. Snead; Wade F. Zeno; Grace Kago; Ryan W. Perkins; J Blair Richter; Chi Zhao; Eileen M. Lafer; Jeanne C. Stachowiak

Interestingly, previous structural studies using cryo-electron microscopy have reported limited observations of tubular N-BAR scaffolds formed from full-length amphiphysin (Adam et al., 2015; . These structures have been observed on membrane substrates containing a majority of negatively-charged lipids, which are thought to provide a strong electrostatic driving force for scaffold assembly (Adam et al., 2015; . Therefore, we performed tethered vesicle fission experiments using a similar membrane composition (Fig. S3) . Here, the onset of membrane fission occurred at somewhat higher Amph-FL concentration, 350 nM ( Fig. S3 ) in comparison to 75 nM ( Fig. 2B -F). These results demonstrate that high concentrations of negatively charged lipids cannot prevent membrane fission as protein concentration increases. Indeed, the cryoelectron microscopy studies cited above suggest that long-range scaffolds assembled from full-length protein were more rare . Moreover, these studies employed buffers that lacked small monovalent ions (Adam et al., 2015; , conditions known to favor extension of disordered domains owing to reduced electrostatic screening (Srinivasan et al., 2014) . This environment likely enabled the disordered domains to pack more efficiently around the scaffold, in line with the needle-like densities seen protruding from the N-BAR scaffold (Adam et al., 2015) .