N-terminal Mad Homology 1 (MH1) domain in SMAD2 and SMAD3
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. MH1 binds to the DNA 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 is found in SMAD2 as well as SMAD3. SMAD2 mediates the signal of the transforming growth factor (TGF)-beta, and thereby regulates multiple cellular processes, such as cell proliferation, apoptosis, and differentiation. It plays a role in the transmission of extracellular signals from ligands of the TGF-beta superfamily growth factors into the cell nucleus. SMAD3 modulates signals of activin and TGF-beta. It binds SMAD4, enabling its transmigration into the nucleus where it forms complexes with other proteins and acts as a transcription factor. Increased SMAD3 activity has been implicated in the pathogenesis of scleroderma.