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Structures of an ActRIIB:activin A complex reveal a novel binding mode for TGF-beta ligand:receptor interactions

Thomas B Thompson1, Teresa K Woodruff, Theodore S Jardetzky

  • 1Department of Biochemistry, Northwestern University, 2205 Tech Drive, Evanston, IL 60208, USA.

The EMBO Journal
|March 28, 2003
PubMed

Insights

The crystal structure reveals how activin A (a TGF-beta superfamily member) binds to its receptor ActRIIB. This binding mode differs from other TGF-beta ligands and may influence cell signaling.

Area of Science:

  • Molecular Biology
  • Structural Biology
  • Cell Signaling

Background:

  • Transforming Growth Factor-beta (TGF-beta) superfamily ligands and receptors are crucial for development and immune function.
  • Activins, a subgroup of TGF-beta ligands, regulate cell differentiation, proliferation, activation, and apoptosis.
  • Activins signal via complexes with type I and type II serine/threonine kinase receptors.

Purpose of the Study:

  • To determine the crystal structure of activin A bound to the extracellular domain of the type II receptor, ActRIIB.
  • To elucidate the molecular details of the activin A-ActRIIB interaction.
  • To understand how this interaction may influence cellular signaling pathways.

Main Methods:

  • X-ray crystallography was used to solve the structure of the activin A-ActRIIB complex.
  • Structural analysis focused on the binding interface and conformational properties of activin A.

Main Results:

  • The crystal structure reveals activin A adopts a compact, folded-back conformation, distinct from other TGF-beta ligands.
  • ActRIIB binds to the outer edges of the activin A dimer's finger regions.
  • The observed binding mode positions receptors closely, suggesting a mechanism for recruiting type I receptors.

Conclusions:

  • The unique binding mode of activin A to ActRIIB differs from TGF-beta3 interactions.
  • The dimeric structure of activin A and its receptor interactions provide insights into TGF-beta superfamily signaling.
  • Conformational diversity in TGF-beta ligand dimers may play a role in regulating cellular responses.

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