Structure Function Relationship of Smads

Smads are evolutionarily conserved. The name Smad was coined to reflect it being the vertebrate homologue of the Drosophila Mad and the C. elegans Sma. The R-Smads and Smad4 contain conserved N-and C-terminal regions, also designated as the MH1 (Mad Homology 1) and MH2 (Mad Homology 2)

domains, respectively, separated by a divergent proline-rich linker region (Fig. 11.3). Smad2 and Smad3 are highly homologous with each other, sharing over 90% homology. They are divergent in the proline-rich linker region. In addition, Smad2 contains two stretches of amino acids that are not present in Smad3. The first stretch is 10 amino acids. The second stretch is 30 amino acids that is encoded by a separate exon (exon 3) (Takenoshita et al., 1998). The presence of these 30

amino acids interferes with Smad2 binding to DNA (Dennler et al., 1998; Shi et al., 1998; Yagi et al., 1999; Shi, 2001). Smad2 and Smad3 have overlapping as well as distinct properties and functions (Liu, 2003; Roberts et al., 2003). Smadl, Smad5 and Smad8 share over 90% homology. The R-Smads are more similar with each other than with Smad4. The C-terminal domains of Smad6 and Smad7 are similar to those of the R-Smads and Smad4 but do not contain the SSXS motif for receptor

N Domain (MHl)


C Domain (MH2)

Receptor-Regulated Smads

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