title: Determinants of ligand binding specificity in the glial cell line-derived neurotrophic factor family receptor alpha S.
abstract: The glial cell line-derived neurotrophic factor (GDNF) family comprise a subclass of cystine-knot superfamily ligands that interact with a multisubunit receptor complex formed by the c-Ret tyrosine kinase and a cystine-rich glycosyl phosphatidylinositol-anchored binding subunit called GDNF family receptor alpha (GFRalpha). All four GDNF family ligands utilize c-Ret as a common signaling receptor, whereas specificity is conferred by differential binding to four distinct GFRalpha homologues. To understand how the different GFRalphas discriminate ligands, we have constructed a large set of chimeric and truncated receptors and analyzed their ligand binding and signaling capabilities. The major determinant of ligand binding was found in the most conserved region of the molecule, a central domain predicted to contain four conserved alpha helices and two beta strands. Distinct hydrophobic and positively charged residues in this central region were required for binding of GFRalpha1 to GDNF. Interaction of GFRalpha1 and GFRalpha2 with GDNF and neurturin required distinct subsegments within this central domain, which allowed the construction of chimeric receptors that responded equally well to both ligands. C-terminal segments adjacent to the central domain are necessary and have modulatory function in ligand binding. In contrast, the N-terminal domain was dispensable without compromising ligand binding specificity. Ligand-independent interaction with c-Ret also resides in the central domain of GFRalpha1, albeit within a distinct and smaller region than that required for ligand binding. Our results indicate that the central region of this class of receptors constitutes a novel binding domain for cystine-knot superfamily ligands.
authors.affiliation: Division of Molecular Neurobiology, Department of Neuroscience, Karolinska Institute, 17177 Stockholm, Sweden.
authors.forename: R P
authors.initials: RP
authors.lastname: Scott
authors.forename: C F
authors.initials: CF
authors.lastname: Ibanez
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D002645:Chickens; D002522:Chlorocebus aethiops; D029721:Drosophila Proteins; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009457:Neuroglia / Q000378:metabolism*; D017433:Protein Structure, Secondary; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051096:Proto-Oncogene Proteins c-ret; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014162:Transfection
chemical_list: D029721:Drosophila Proteins; C495040:Gdnf protein, mouse; C495041:Gdnf protein, rat; C494988:Gfra1 protein, mouse; C494991:Gfra2 protein, mouse; C494992:Gfra2 protein, rat; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D008024:Ligands; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C494999:Ret protein, mouse; C495001:Ret protein, rat