A two-site flexible clamp mechanism for RET-GDNF-GFRα1 assembly reveals both conformational adaptation and strict geometric spacing

Abstract

RET receptor tyrosine kinase plays vital developmental and neuroprotective roles in metazoans. GDNF family ligands (GFLs) when bound to cognate GFRα co-receptors recognise and activate RET stimulating its cytoplasmic kinase function. The principles for RET ligand-co-receptor recognition are incompletely understood. Here we report a crystal structure of the cadherin-like module (CLD1-4) from zebrafish RET revealing interdomain flexibility between CLD2-CLD3. Comparison with a cryo-EM structure of a ligand-engaged zebrafish RETECD-GDNF-GFRα1 complex indicates conformational changes within a clade-specific CLD3 loop adjacent to co-receptor. Our observations indicate RET is a molecular clamp with a flexible calcium-dependent arm that adapts to different GFRα co-receptors, while its rigid arm recognises a GFL dimer to align both membrane-proximal cysteine-rich domains. We also visualise linear arrays of RETECD-GDNF-GFRα1 suggesting a conserved contact stabilises higher-order species. Our study reveals ligand-co-receptor recognition by RET involves both receptor plasticity and strict spacing of receptor dimers by GFL ligands.

RET receptor signaling: Function in development, metabolic disease, and cancer

“…Because of this unique C-clamp shape, two RET molecules are recruited onto dimeric GFL-GFRα complexes, and the two cysteine-rich domains of RET are brought into close proximity, thereby promoting dimer formation and activation of the activity of the intracellular tyrosine kinase domain. 33 – 35 )…”