This is the MH2 (MAD homology 2) domain found at the carboxy terminus of MAD related proteins such as Smads. This domain is separated from the MH1 domain by a non-conserved linker region. The MH2 domain mediates interaction with a wide variety of proteins and provides specificity and selectivity to Smad function and also is critical for mediating interactions in Smad oligomers. Unlike MH1, MH2 does not bind DNA. The well-studied MH2 domain of Smad4 is composed of five alpha helices and three loops enclosing a beta sandwich. Smads are involved in the propagation of TGF-beta signals by direct association with the TGF-beta receptor kinase which phosphorylates the last two Ser of a conserved 'SSXS' motif located at the C-terminus of MH2 [1-3].

1: Mammalian dwarfins are phosphorylated in response to transforming growth factor beta and are implicated in control of cell growth. Yingling JM, Das P, Savage C, Zhang M, Padgett RW, Wang XF; Proc Natl Acad Sci U S A 1996;93:8940-8944. PMID:8799132

2: Drosophila Mad binds to DNA and directly mediates activation of vestigial by Decapentaplegic. Kim J, Johnson K, Chen HJ, Carroll S, Laughon A; Nature 1997;388:304-308. PMID:9230443

3: The Smads. Attisano L, Tuen Lee-Hoeflich S; Genome Biol 2001;2:REVIEWS3010. PMID:11532220