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MH1 Domain

Structure:

No ImageThe structure shown is the Smad3 MH1 domain in complex with the Smad-binding element (SBE) DNA sequence. Each of the MH1 domains consists of four alpha-helices, six short beta-strands, five loops, and binds identically and independently to the SBE sequence 5-GTCT-3 or 5-AGAC-3 through hydrogen bonds to the DNA bases and phosphodiester backbone. An 11-residue beta-hairpin, formed between strands B2 and B3, protrudes outward from the globular MH1 core and is responsible for DNA contact. This contact is stabilized by a number of surrounding water molecules. Additionally, a zinc atom is buried deep within the MH1 structure, where in its absence the affinity of the MH1/DNA complex is compromised.

Structure Reference: Chai, J. et al. (2003) J. Biol. Chem. 278(22), 20327-20331. PDB: 1OZJ


Domain binding and function:
The MH1, short for Mad homology 1, domain is typically found at the N-terminus of Smad proteins and is responsible for DNA binding activity as well as negative regulation of the Smad C-terminal MH2 domain. The binding of the MH1 domain is specific to the minimal unique 4-bp sequence called the Smad-box of the sequence 5-GTCT-3 or 5-AGAC-3. The ability for MH1 to bind the SBE is critical for Smad-mediated activation of specific ligand-responsive genes in TGF-beta signaling.
Examples of Proteins: 
MH1 domain proteins

Smad family of proteins
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