Quantifying Membrane Curvature Generation of Drosophila Amphiphysin N-BAR Domains.

Biological membrane functions are coupled to membrane curvature, the regulation of which often involves membrane-associated proteins. The membrane-binding N-terminal amphipathic helix-containing Bin/Amphiphysin/Rvs (N-BAR) domain of amphiphysin is implicated in curvature generation and maintenance. Improving the mechanistic understanding of membrane curvature regulation by N-BAR domains requires quantitative experimental characterization. We have measured tube-pulling force modulation by the N-BAR domain of Drosophila amphiphysin (DA-N-BAR) bound to tubular membranes pulled from micropipet-aspirated giant vesicles. We observed that fluorescently labeled DA-N-BAR showed significantly higher protein density on tubes compared to the connected low-curvature vesicle membrane. Furthermore, we found the equilibrium tube-pulling force to be systematically dependent on the aqueous solution concentration of DA-N-BAR, thereby providing the first quantitative assessment of spontaneous curvature generation. At suffici...