Transcriptional modulator activated by BMP (bone morphogenetic proteins) type 1 receptor kinase. SMAD5 is a receptor-regulated SMAD (R-SMAD) (By similarity). Required for angiogenesis. May form trimers with the co-SMAD SMAD4. Interacts with PEBP2-alpha subunit and SMURF1. Interacts with SUV39H1 and SUV39H2. Interacts (via MH2 domain) with LEMD3 (By similarity). Interacts with WWP1. Interacts with TMEM119 (PubMed:21239498). Interacts with ZNF8 (PubMed:12370310). Interacts with RANBP3L (By similarity). In the cytoplasm in the absence of ligand. Migration to the nucleus when complexed with SMAD4 (By similarity). Phosphorylated on serine by BMP (bone morphogenetic proteins) type 1 receptor kinase. Ubiquitin-mediated proteolysis by SMAD-specific E3 ubiquitin ligase SMURF1. Belongs to the dwarfin/SMAD family.