title: Identification of a Novel TGF-β-Binding Site in the Zona Pellucida C-terminal (ZP-C) Domain of TGF-β-Receptor-3 (TGFR-3).
abstract: The zona pellucida (ZP) domain is present in extracellular proteins such as the zona pellucida proteins and tectorins and participates in the formation of polymeric protein networks. However, the ZP domain also occurs in the cytokine signaling co-receptor transforming growth factor β (TGF-β) receptor type 3 (TGFR-3, also known as betaglycan) where it contributes to cytokine ligand recognition. Currently it is unclear how the ZP domain architecture enables this dual functionality. Here, we identify a novel major TGF-β-binding site in the FG loop of the C-terminal subdomain of the murine TGFR-3 ZP domain (ZP-C) using protein crystallography, limited proteolysis experiments, surface plasmon resonance measurements and synthetic peptides. In the murine 2.7 Å crystal structure that we are presenting here, the FG-loop is disordered, however, well-ordered in a recently reported homologous rat ZP-C structure. Surprisingly, the adjacent external hydrophobic patch (EHP) segment is registered differently in the rat and murine structures suggesting that this segment only loosely associates with the remaining ZP-C fold. Such a flexible and temporarily-modulated association of the EHP segment with the ZP domain has been proposed to control the polymerization of ZP domain-containing proteins. Our findings suggest that this flexibility also extends to the ZP domain of TGFR-3 and might facilitate co-receptor ligand interaction and presentation via the adjacent FG-loop. This hints that a similar C-terminal region of the ZP domain architecture possibly regulates both the polymerization of extracellular matrix proteins and cytokine ligand recognition of TGFR-3.
authors.affiliation: Lehrstuhl fuer Biotechnik, Department of Biology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Uschi
authors.initials: U
authors.lastname: Diestel
authors.forename: Marcus
authors.initials: M
authors.lastname: Resch
authors.forename: Kathrin
authors.initials: K
authors.lastname: Meinhardt
authors.forename: Sigrid
authors.initials: S
authors.lastname: Weiler
authors.forename: Tina V
authors.initials: TV
authors.lastname: Hellmann
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Mueller
authors.forename: Joachim
authors.initials: J
authors.lastname: Nickel
authors.forename: Jutta
authors.initials: J
authors.lastname: Eichler
authors.forename: Yves A
authors.initials: YA
authors.lastname: Muller
mesh_terms: D000818:Animals; D001665:Binding Sites; D060326:Chemistry Techniques, Synthetic; D002850:Chromatography, Gel; D002942:Circular Dichroism; D003461:Crystallography; D000067493:Dynamic Light Scattering; D057809:HEK293 Cells; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D000072417:Protein Domains; D055550:Protein Stability; D011509:Proteoglycans / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis; D018125:Receptors, Transforming Growth Factor beta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012996:Solutions; D013045:Species Specificity; D020349:Surface Plasmon Resonance
chemical_list: D011509:Proteoglycans; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; D012996:Solutions; C071736:betaglycan