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  • The EMBO Journal (2003) 22, 4607 - 4615
  • doi:10.1093/emboj/cdg445

Structure of integrin alpha5bold beta1 in complex with fibronectin

Junichi Takagi1,2,3,6, Konstantin Strokovich4,6, Timothy A. Springer1,5 and Thomas Walz4

  1. The Center for Blood Research, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
  2. Department of Pediatrics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
  3. Present address: Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan
  4. Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
  5. Department of Pathology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
  6. J.Takagi and K.Strokovich contributed equally to this work

Correspondence to:

Junichi Takagi, E-mail: takagi@protein.osaka-u.ac.jp

Thomas Walz, E-mail: twalz@hms.harvard.edu

Received 8 May 2003; Accepted 22 July 2003; Revised 21 July 2003

The membrane-distal headpiece of integrins has evolved to specifically bind large extracellular protein ligands, but the molecular architecture of the resulting complexes has not been determined. We used molecular electron microscopy to determine the three-dimensional structure of the ligand-binding headpiece of integrin alpha5beta1 complexed with fragments of its physiological ligand fibronectin. The density map for the unliganded alpha5beta1 headpiece shows a 'closed' conformation similar to that seen in the alphaVbeta3 crystal structure. By contrast, binding to fibronectin induces an 'open' conformation with a dramatic, approx80° change in the angle of the hybrid domain of the beta subunit relative to its I-like domain. The fibronectin fragment binds to the interface between the beta-propeller and I-like domains in the integrin headpiece through the RGD-containing module 10, but direct contact of the synergy-region-containing module 9 to integrin is not evident. This finding is corroborated by kinetic analysis of real-time binding data, which shows that the synergy site greatly enhances kon but has little effect on the stability or koff of the complex.

  • Keywords:

    • conformational change,
    • electron microscopy,
    • fibronectin,
    • integrin,
    • single-particle analysis