Abstract
Bin/amphiphysin/Rvs (BAR) domain proteins regulate curvature on cellular membranes by directly interacting with negatively charged phospholipids and self-assembling into higher-order scaffolds. However, the in vivo significance of these activities and the molecular mechanisms by which they are regulated are poorly understood. Here, we show that the Fer-CIP3 homology-BAR (F-BAR) domain of Nervous Wreck (Nwk) is required for its function in vivo at the Drosophila neuromuscular junction (NMJ) and is regulated by C-terminal sequences. The C-terminal Nwk SH3 domains directly interact with the F-BAR domain to inhibit membrane deformation in cells and increase the minimum membrane charge required for Nwk binding in vitro. Surprisingly, we found that reduced Nwk membrane-binding results in enhanced F-BAR domain self-assembly and membrane deformation in vitro. Our data suggest a new feature of F-BAR domain activity: optimal deformation occurs only within a limited range of membrane charge, and high levels of negatively charged phospholipids actually decouple Nwk membrane binding and deformation. Auto-regulation may serve to widen the range of lipid compositions at which deformation can occur within the cell. Our findings suggest that membrane composition may be even more critical than previously thought for the regulation of F-BAR domain assembly and activity, and that higher-order assembly is an important in vivo function of F-BAR domains.