E3 ubiquitin-protein ligase that acts as a negative regulator of BMP signaling pathway. Mediates ubiquitination and degradation of SMAD1 and SMAD5, 2 receptor-regulated SMADs specific for the BMP pathway. Promotes ubiquitination and subsequent proteasomal degradation of TRAF family members and RHOA. Promotes ubiquitination and subsequent proteasomal degradation of MAVS (PubMed:23087404). Plays a role in dendrite formation by melanocytes (PubMed:23999003). 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. Interacts (via HECT domain) with FBXL15 (via LRR repeats). Interacts with SMAD7 and TGFBR1; SMAD7 recruits SMURF1 to TGFBR1 and regulates TGF-beta receptor degradation. Interacts with MAVS; the interaction is mediated by NDFIP1 (PubMed:23087404). Expressed in melanocytes (PubMed:23999003). The C2 domain mediates membrane localization and substrate selection. Auto-ubiquitinated in presence of NDFIP1 (PubMed:23087404). Ubiquitinated by the SCF(FBXL15) complex at Lys-381 and Lys-383, leading to its degradation by the proteasome. Lys-383 is the primary ubiquitination site.