Anti-phospho Smad1/Smad5/Smad8 (Ser463/465) from rabbit, purified by affinity chromatography

Mothers against decapentaplegic homolog 1 (UniProt Q15797; also known as BSP-1, hSMAD1, JV4-1, MAD homolog 1, Mothers against DPP homolog 1, Mad-related protein 1, SMAD 1, SMAD family member 1, Smad1, Transforming growth factor-beta-signaling protein 1) is encoded by the SMAD1 (also known as BSP1, MADH1, MADR1) gene (Gene ID 4086) in human. Mammalian SMADs constitute a family of transcription factors that are subdivided into three groups. SMAD1, 2, 3, 5, and 9 (a.k.a. SMAD8) are receptor-regulated SMADs or R-SMADs. SMAD4 is the only known mammalian common mediator SMAD or Co-SMAD and it mediates both the TGF- and BMP signalling pathways. SMAD6 and SMAD7 are inhibitory SMADs or I-SMADs that block the activation of R-SMADs by Co-SMAD via competitive binding. SMADs share a similar structure feature consisting of the conserved N-terminal Mad-homology 1 (MH1; a.a. 12-136 of hSMAD1, a.a. 13-137 of hSMAD2, a.a. 16-140 of hSMAD8) and C-terminal MH2 (a.a. 271-465 of hSMAD1 & hSMAD2, a.a. 273-467 of hSMAD8) domains joined by a non-conserved linker region among SMADs. MH1 domain in R-SMADs and Co-SMADs contains N-terminus nuclear localization signals (NLS), while SMAD4 has nuclear export signals (NES) in this domain. The MH2 domain is responsible for gene transactivation as well as for mediating SMAD-receptor, SMAD-SMAD, SMAD-coactivators and SMAD-corepressors interactions. A TGF- ligand (TGF- for SMAD2/3 and BMP for SMAD1/5/8) initiates signalling by binding and engaging type I and type II receptor serine/threonine kinases on the cell surface, allowing T RII-dependent phosphorylation of T RI kinase domain, which then instigates signalling by phosphorylating the last two serine residues within the conserved C-terminal end Ser-Ser-X-Ser (SSXS) motif of SMAD proteins.