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

Fig. S2G-I shows representative FCS traces and fits for Amph CTD ∆SH3, AP180 CTD, and transferrin, with mean values of / ± first s.d. reported next to each trace. The hydrodynamic radius, 6 , of each protein is also reported next to each trace. AP180 CTD was used as a calibration standard to compute 6 of Amph CTD ∆SH3 , as / is directly proportional to 6 . AP180 CTD is a disordered protein with a radius that has been wellcharacterized Kalthoff et al., 2002) , making it an appropriate calibration standard. This calibration approach also yielded a radius for transferrin that was consistent with its expected radius (Hall et al., 2002) , confirming the validity of our approach. The radius of Amph CTD ∆SH3 was taken as 5 nm in estimates of membrane coverage by proteins in Fig. 3D , S2A-F, and S2K-M. This value was chosen based on previous studies which found that the radius of gyration of a disordered protein is approximately 1.2-fold greater than the hydrodynamic radius (Hofmann et al., 2012; Sherman and Haran, 2006 ). (Zhang and Han, 1996) . Because / is directly proportional to 6 , the increase in / at 10 mM NaCl indicates an increase in 6 , likely owing to reduced charge screening which expands and extends the disordered protein (Srinivasan et al., 2014) . Similarly, the decrease in / at 1 M NaCl indicates a decrease in 6 , owing to enhanced charge screening which compacts the disordered protein.