Cell Reports (Sep 2014)

RET Recognition of GDNF-GFRα1 Ligand by a Composite Binding Site Promotes Membrane-Proximal Self-Association

  • Kerry M. Goodman,
  • Svend Kjær,
  • Fabienne Beuron,
  • Phillip P. Knowles,
  • Agata Nawrotek,
  • Emily M. Burns,
  • Andrew G. Purkiss,
  • Roger George,
  • Massimo Santoro,
  • Edward P. Morris,
  • Neil Q. McDonald

DOI
https://doi.org/10.1016/j.celrep.2014.08.040
Journal volume & issue
Vol. 8, no. 6
pp. 1894 – 1904

Abstract

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The RET receptor tyrosine kinase is essential to vertebrate development and implicated in multiple human diseases. RET binds a cell surface bipartite ligand comprising a GDNF family ligand and a GFRα coreceptor, resulting in RET transmembrane signaling. We present a hybrid structural model, derived from electron microscopy (EM) and low-angle X-ray scattering (SAXS) data, of the RET extracellular domain (RETECD), GDNF, and GFRα1 ternary complex, defining the basis for ligand recognition. RETECD envelopes the dimeric ligand complex through a composite binding site comprising four discrete contact sites. The GFRα1-mediated contacts are crucial, particularly close to the invariant RET calcium-binding site, whereas few direct contacts are made by GDNF, explaining how distinct ligand/coreceptor pairs are accommodated. The RETECD cysteine-rich domain (CRD) contacts both ligand components and makes homotypic membrane-proximal interactions occluding three different antibody epitopes. Coupling of these CRD-mediated interactions suggests models for ligand-induced RET activation and ligand-independent oncogenic deregulation.