N-terminal Mad Homology 1 (MH1) domain of receptor regulated SMADs
The MH1 is a small DNA-binding domain present in SMAD (small mothers against decapentaplegic) family of proteins, which are signal transducers and transcriptional modulators that mediate multiple signaling pathways. It binds to the major groove in an unusual manner via a beta hairpin structure. It negatively regulates the functions of the MH2 domain, the C-terminal domain of SMAD. This MH1 domain is found in all receptor regulated SMADs (R-SMADs) including SMAD1, SMAD2, SMAD3, SMAD5 and SMAD9. SMAD1 plays an essential role in bone development and postnatal bone formation through activation by bone morphogenetic protein (BMP) type 1 receptor kinase. SMAD2 regulates multiple cellular processes, such as cell proliferation, apoptosis and differentiation, while SMAD3 modulates signals of activin and TGF-beta. SMAD4, a common mediator SMAD (co-SMAD) binds R-SMADs, forming an oligomeric complex that binds to DNA and serves as a transcription factor. SMAD5 is involved in bone morphogenetic proteins (BMP) signal modulation, possibly playing a role in the pathway involving inhibition of hematopoietic progenitor cells by TGF-beta. SMAD9 (also known as SMAD8) can mediate the differentiation of mesenchymal stem cells (MSCs) into tendon-like cells by inhibiting the osteogenic pathway
Jiyao W et al.(2023). "The conserved domain database in 2023.",