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

RET receptor tyrosine kinase plays vital developmental and neuroprotective roles in metazoans. GDNF family ligands (GFLs) when bound to cognate GFRα co-receptors recognize 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 and CLD3. Comparison with a cryo-electron microscopy structure of a ligand-engaged zebrafish RETECD-GDNF-GFRα1a complex indicates conformational changes within a clade-specific CLD3 loop adjacent to the co-receptor. Our observations indicate that RET is a molecular clamp with a flexible calcium-dependent arm that adapts to different GFRα co-receptors, while its rigid arm recognizes a GFL dimer to align both membrane-proximal cysteine-rich domains. We also visualize linear arrays of RETECD-GDNF-GFRα1a suggesting that a conserved contact stabilizes higher-order species. Our study reveals that ligand-co-receptor recognition by RET involves both receptor plasticity and strict spacing of receptor dimers by GFL ligands

Explosive expansion of beta gamma-crystallin genes in the ancestral vertebrate (vol 71, 219, 2010)

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Crystal structures of SAMHD1 inhibitor complexes reveal the mechanism of water-mediated dNTP hydrolysis

SAMHD1 catalyses the hydrolysis of dNTPs into 2′-deoxynucleosides and triphosphate and is an important regulator of cellular dNTP homeostasis. Here, the authors provide insights into the catalytic mechanism of SAMHD1 by performing kinetic measurements and determining crystal structures of α-β-imido-dNTP inhibitor complexes, which reveal a bi-metallic iron-magnesium centre and catalytic hydroxyl molecule in the active site of the enzyme

Architecture and regulation of a GDNF-GFRa1 synaptic adhesion assembly

Glial-cell line derived neurotrophic factor (GDNF) bound to its co-receptor GFRa1 stimulates the RET receptor tyrosine kinase, promoting neuronal survival and neuroprotection. The GDNF-GFRa1 complex also acts as a synaptic cell adhesion independently of RET. Here, we describe the structure of a decameric GDNF-GFRa1 assembly determined by crystallography and electron microscopy, revealing two GFRa1 pentamers bridged by five GDNF dimers. We reconsitituted the assembly in vitro between pairs of adhering liposomes and used cryo-electron tomography to visualize how the complex fulfils its membrane adhesion function. The GFRa1:GFRa1 pentameric interface was further validated both in vitro by native PAGE and in cellulo by cell-clustering and dendritic spine assays. Finally, we provide biochemical and cell-based evidence that RET and heparan sulfate cooperate to prevent assembly of the adhesion complex by competing for the adhesion interface. Our results provide a mechanistic framework to understand GDNF-driven cell adhesion, its relationship to trophic signalling, and the central role of GFRa1. Houghton, FM1, Adams SE^1, Ríos AS2, Masino, L3, Purkiss AG3, Briggs DC1, Ledda, F2, & McDonald N.Q.1,4