Required to coordinate membrane tubulation with reorganization of the actin cytoskeleton during endocytosis. Essential for autophagy of intracellular bacterial pathogens (By similarity). Promotes cdc42-induced actin polymerization by activating the wasl-waspip complex, the predominant form of wasl/n-wasp in cells. Homodimerizes, the dimers can polymerize end-to-end to form filamentous structures (By similarity). Interacts with GTP-bound cdc42 and wasl/n-wasp. The F-BAR domain binds the phospholipid membrane with its concave surface. The end-to-end polymerization of dimers of these domains provides a curved surface that fits best membranes with around 600 A diameter, and may drive tubulation (By similarity). Belongs to the FNBP1 family.