E3 ubiquitin-protein ligase that acts as a negative regulator of BMP signaling pathway (By similarity). Mediates ubiquitination and degradation of SMAD1 and SMAD5, 2 receptor-regulated SMADs specific for the BMP pathway (By similarity). Promotes ubiquitination and subsequent proteasomal degradation of TRAF family members and RHOA (By similarity). Promotes ubiquitination and subsequent proteasomal degradation of MAVS (PubMed:23087404). Plays a role in dendrite formation by melanocytes (By similarity). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with TRAF4 (By similarity). Interacts (via HECT domain) with FBXL15 (via LRR repeats) (By similarity). Interacts with SMAD7 and TGFBR1; SMAD7 recruits SMURF1 to TGFBR1 and regulates TGF-beta receptor degradation (By similarity). Interacts with MAVS; the interaction is mediated by NDFIP1 (PubMed:23087404). The C2 domain mediates membrane localization and substrate selection. Auto-ubiquitinated in presence of NDFIP1. Ubiquitinated by the SCF(FBXL15) complex at Lys-355 and Lys-357, leading to its degradation by the proteasome. Lys-357 is the primary ubiquitination site.