Figure 1

Primary structure and relationships of Smads. (a) The conserved Mad homology 1 (MH1) and Mad homology 2 (MH2) domains are separated by a proline-rich nonconserved linker region. (b) Structure of the Smad3 MH1 domain (reproduced with permission from [13]). H2, helix H2; β, β hairpin, which contacts DNA. (c) Structure of the Smad4 MH2 and Smad activation domains (reproduced with permission from [26]). H1-H5, helices; L1-L3, loops. New features not present in the first Smad4 MH2 crystal structure [17] are colored green. The location of bound sulfate ions from the crystallization medium are in blue. (d) Relationship dendrogram for the Smad family, including members from Drosophila (D), C. elegans (C), S. mansoni (S) and human (the remainder). The subgrouping of Smads into the common Smads (co-Smads), receptor-regulated (R-Smads) and inhibitory (I-Smads) is indicated. C. elegans Smads, which have not been subject to extensive biochemical characterization, have been excluded from this subgrouping. This dendrogram was generated using the MacVector program.