Structural basis of Smad2 recognition by the Smad anchor for receptor activation.

The Smad proteins mediate transforming growth factor-beta (TGFbeta) signaling from the transmembrane serine-threonine receptor kinases to the nucleus. The Smad anchor for receptor activation (SARA) recruits Smad2 to the TGFbeta receptors for phosphorylation. The crystal structure of a Smad2 MH2 domain in complex with the Smad-binding domain (SBD) of SARA has been determined at 2.2 angstrom resolution. SARA SBD, in an extended conformation comprising a rigid coil, an alpha helix, and a beta strand, interacts with the beta sheet and the three-helix bundle of Smad2. Recognition between the SARA rigid coil and the Smad2 beta sheet is essential for specificity, whereas interactions between the SARA beta strand and the Smad2 three-helix bundle contribute significantly to binding affinity. Comparison of the structures between Smad2 and a comediator Smad suggests a model for how receptor-regulated Smads are recognized by the type I receptors.

[1]  Xin Chen,et al.  A transcriptional partner for MAD proteins in TGF-β signalling , 1996, Nature.

[2]  E. Lai,et al.  FAST-2 Is a Mammalian Winged-Helix Protein Which Mediates Transforming Growth Factor β Signals , 1999, Molecular and Cellular Biology.

[3]  K. Sharp,et al.  Protein folding and association: Insights from the interfacial and thermodynamic properties of hydrocarbons , 1991, Proteins.

[4]  R. Derynck,et al.  A kinase subdomain of transforming growth factor‐β (TGF‐β) type I receptor determines the TGF‐β intracellular signaling specificity , 1997 .

[5]  J. Massagué.  TGF-beta signal transduction. , 1998, Annual review of biochemistry.

[6]  P. Kraulis.  A program to produce both detailed and schematic plots of protein structures , 1991 .

[7]  J. Massagué,et al.  Determinants of specificity in TGF-beta signal transduction. , 1998, Genes & development.

[8]  Jeffrey L. Wrana,et al.  Mechanism of activation of the TGF-β receptor , 1994, Nature.

[9]  Yigong Shi,et al.  A structural basis for mutational inactivation of the tumour suppressor Smad4 , 1997, Nature.

[10]  S. Willis,et al.  Formation and activation by phosphorylation of activin receptor complexes. , 1996, Molecular endocrinology.

[11]  Liliana Attisano,et al.  SARA, a FYVE Domain Protein that Recruits Smad2 to the TGFβ Receptor , 1998, Cell.

[12]  J. Navaza,et al.  AMoRe: an automated package for molecular replacement , 1994 .

[13]  Yigong Shi,et al.  The L3 loop: a structural motif determining specific interactions between SMAD proteins and TGF‐β receptors , 1998, The EMBO journal.

[14]  J. Massagué,et al.  GS domain mutations that constitutively activate T beta R‐I, the downstream signaling component in the TGF‐beta receptor complex. , 1995, The EMBO journal.

[15]  Philip D. Jeffrey,et al.  Crystal structure of the p27Kip1 cyclin-dependent-kinase inibitor bound to the cyclin A–Cdk2 complex , 1996, Nature.

[16]  Morgan Huse,et al.  Crystal Structure of the Cytoplasmic Domain of the Type I TGF β Receptor in Complex with FKBP12 , 1999, Cell.

[17]  R. Derynck,et al.  Transforming Growth Factor-β (TGF-β)-induced Down-regulation of Cyclin A Expression Requires a Functional TGF-β Receptor Complex , 1995, The Journal of Biological Chemistry.

[18]  Takeo Iwama,et al.  Higher frequency of Smad4 gene mutation in human colorectal cancer with distant metastasis , 1999, Oncogene.

[19]  Kohei Miyazono,et al.  TGF-β signalling from cell membrane to nucleus through SMAD proteins , 1997, Nature.

[20]  J. Zou,et al.  Improved methods for building protein models in electron density maps and the location of errors in these models. , 1991, Acta crystallographica. Section A, Foundations of crystallography.