Structural basis for EGFR ligand sequestration by Argos


Members of the epidermal growth factor receptor (EGFR) or ErbB/HER family and their activating ligands are essential regulators of diverse developmental processes1,2. Inappropriate activation of these receptors is a key feature of many human cancers3, and its reversal is an important clinical goal. A natural secreted antagonist of EGFR signalling, called Argos, was identified in Drosophila4. We showed previously that Argos functions by directly binding (and sequestering) growth factor ligands that activate EGFR5. Here we describe the 1.6-Å resolution crystal structure of Argos bound to an EGFR ligand. Contrary to expectations4,6, Argos contains no EGF-like domain. Instead, a trio of closely related domains (resembling a three-finger toxin fold7) form a clamp-like structure around the bound EGF ligand. Although structurally unrelated to the receptor, Argos mimics EGFR by using a bipartite binding surface to entrap EGF. The individual Argos domains share unexpected structural similarities with the extracellular ligand-binding regions of transforming growth factor-β family receptors8. The three-domain clamp of Argos also resembles the urokinase-type plasminogen activator (uPA) receptor, which uses a similar mechanism to engulf the EGF-like module of uPA9. Our results indicate that undiscovered mammalian counterparts of Argos may exist among other poorly characterized structural homologues. In addition, the structures presented here define requirements for the design of artificial EGF-sequestering proteins that would be valuable anti-cancer therapeutics.

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Figure 1: Structure of the Argos–Spitz complex.
Figure 2: Argos has three similar domains that resemble the three-finger toxin fold of TGF-β receptors.
Figure 3: Spitz-binding interactions.
Figure 4: Argos, EGFR and structural homologues entrap the EGF domain with two binding sites.

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We thank members of the Lemmon and Ferguson laboratories, G. Van Duyne and J. Shorter for advice and critical reading of the manuscript. This work was supported by grants from the National Institutes of Health (to M.A.L.) and the US Army Breast Cancer Research Program (to D.E.K. and M.A.L.).

Author Contributions D.E.K. and M.A.L. conceived and designed the project. D.E.K. was responsible for all construct design and execution of protein biochemistry, crystallization, and data collection. D.E.K. solved and refined the Argos217–SpitzEGF complex structure. S.E.S. solved and refined the structures of uncomplexed Argos217 and SpitzEGF by molecular replacement using datasets collected by D.E.K. K.N. helped with crystal manipulation and data collection. F.S. performed binding studies with Argos and Spitz variants, as well as analytical ultracentrifugation, directed by D.E.K. D.E.K. and M.A.L. interpreted data and wrote the manuscript.

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Correspondence to Mark A. Lemmon.

Additional information

Coordinates have been deposited in the Protein Data Bank under codes 3CA7 (SpitzEGF), 3C9A (Argos217–SpitzEGF complex), and 3CGU (Argos217 alone).

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Supplementary Information

The file contains Supplementary Discussion, Supplementary Figures S1-S7, and Supplementary Table 1 (PDF 5693 kb)

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Klein, D., Stayrook, S., Shi, F. et al. Structural basis for EGFR ligand sequestration by Argos. Nature 453, 1271–1275 (2008) doi:10.1038/nature06978

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