Required to coordinate membrane tubulation with reorganization of the actin cytoskeleton during endocytosis. May bind to lipids such as phosphatidylinositol 4,5-bisphosphate and phosphatidylserine and promote membrane invagination and the formation of tubules. Also promotes CDC42-induced actin polymerization by activating the WASL/N-WASP-WASPIP/WIP complex, the predominant form of WASL/N-WASP in cells. Actin polymerization may promote the fission of membrane tubules to form endocytic vesicles. Essential for autophagy of intracellular bacterial pathogens. Homodimerizes, the dimers can polymerize end-to-end to form filamentous structures (By similarity). Interacts with GTP-bound CDC42 (PubMed:15260990). Interacts with DAAM1, DIAPH1, DIAPH2, DNM1, DNM2 and WASL/N-WASP (PubMed:16326391, PubMed:16630611, PubMed:16418535). Interacts with ATG3 (PubMed:19342671). Interacts (via SH3 domain) with ABI1, WASF2, CDC42 and WIPF1 (PubMed:19798448). 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. Truncated N-terminus.