The decapentaplegic(Dpp),a member of the TGF-βsuperfamily,plays a pivotal role in the control of proliferation,global patterning and induction of specific cell fates during Drosophila development.Mother against Dpp(M...The decapentaplegic(Dpp),a member of the TGF-βsuperfamily,plays a pivotal role in the control of proliferation,global patterning and induction of specific cell fates during Drosophila development.Mother against Dpp(Mad)is the founding member of the conserved Smad protein family which spe-cifically transduces the intracellular TGF-βsignaling cascade.Here we report the 2.80structure of the MH2 domain of Mad(Mad-MH2)that was readily superposed to the mammal Smad-MH2 structures.This unphosphorylated Mad-MH2 forms a symmetric homotrimer in crystals,consistent with the result of the size-exclusion chromatography that Mad-MH2 exhibited a propensity for concentration-dependent oligomerization prior to phosphorylation.Structural analysis revealed that the formation of homotrimeric Mad-MH2 is mainly mediated by contacts involving the extreme C-terminal SSVS motif,and is strengthened by phosphorylation of the last two Ser residues which was confirmed by the gel filtration analysis of the pseudophosphorylated Mad-MH2(DVD).Intriguingly,the homotrimer within an asymmetric unit only possesses two ordered C-terminal tails,reminiscent of the arrangement of the R-Smad/Smad4 complexes,indicating that the subunit with a flexible SSXS motif would be readily replaced by Co-Smad to form a functional heterotrimer.展开更多
基金Supported by National Key Basic Research and Development Program of China(Grant Nos.2006CB503900 and 2007CB914400)China National Funds for Distinguished Young Scientists(Grant No.30425005)
文摘The decapentaplegic(Dpp),a member of the TGF-βsuperfamily,plays a pivotal role in the control of proliferation,global patterning and induction of specific cell fates during Drosophila development.Mother against Dpp(Mad)is the founding member of the conserved Smad protein family which spe-cifically transduces the intracellular TGF-βsignaling cascade.Here we report the 2.80structure of the MH2 domain of Mad(Mad-MH2)that was readily superposed to the mammal Smad-MH2 structures.This unphosphorylated Mad-MH2 forms a symmetric homotrimer in crystals,consistent with the result of the size-exclusion chromatography that Mad-MH2 exhibited a propensity for concentration-dependent oligomerization prior to phosphorylation.Structural analysis revealed that the formation of homotrimeric Mad-MH2 is mainly mediated by contacts involving the extreme C-terminal SSVS motif,and is strengthened by phosphorylation of the last two Ser residues which was confirmed by the gel filtration analysis of the pseudophosphorylated Mad-MH2(DVD).Intriguingly,the homotrimer within an asymmetric unit only possesses two ordered C-terminal tails,reminiscent of the arrangement of the R-Smad/Smad4 complexes,indicating that the subunit with a flexible SSXS motif would be readily replaced by Co-Smad to form a functional heterotrimer.
