title: Structural characterization of twisted gastrulation provides insights into opposing functions on the BMP signalling pathway.
abstract: Twisted gastrulation (Tsg) and chordin are secreted glycoproteins that function together as BMP (bone morphogenetic protein) antagonists to regulate BMP growth factor signalling. Chordin binds to BMPs, preventing them from interacting with their receptors and Tsg is known to strengthen this inhibitory complex. Tsg also acts as a BMP agonist by promoting cleavage of chordin by tolloid-family proteinases. Here we explore the structural mechanism through which Tsg exerts this dual activity. We have characterized the nanoscale structure of human Tsg using in-solution biomolecular analysis and show that Tsg is a globular monomer with a flattened cross shape. Tsg has a high proportion of N-linked glycans, in relation to its molecular weight, which supports a role in solubilising BMPs. Tsg binds with high affinity to the C-terminal region of chordin and was also able to inhibit BMP-7 signalling directly but did not have an effect on BMP-4 signalling. Although both Tsg and mammalian tolloid are involved in chordin cleavage, no interaction could be detected between them using surface plasmon resonance. Together these data suggest that Tsg functions as a BMP-agonist by inducing conformational change in chordin making it more susceptible to tolloid cleavage and as a BMP-antagonist either independently or via a chordin-mediated mechanism. Following single cleavage of chordin by tolloids, Tsg continues to strengthen the inhibitory complex, supporting a role for partially cleaved chordin in BMP regulation.
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Troilo
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK.
authors.forename: Anne L
authors.initials: AL
authors.lastname: Barrett
authors.affiliation: Center for Biochemistry, Medical Faculty, University of Cologne, Cologne, Germany.
authors.forename: Alexandra V
authors.initials: AV
authors.lastname: Zuk
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK; Beamline B21, Diamond Light Source, Harwell Science & Innovation Campus, Didcot, Oxfordshire, UK.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Lockhart-Cairns
authors.affiliation: Center for Biochemistry, Medical Faculty, University of Cologne, Cologne, Germany.
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Wohl
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Bayley
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK.
authors.forename: Rana
authors.initials: R
authors.lastname: Dajani
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Tunnicliffe
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK.
authors.forename: Lewis
authors.initials: L
authors.lastname: Green
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Jowitt
authors.affiliation: Center for Biochemistry, Medical Faculty, University of Cologne, Cologne, Germany; Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sengle
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, M139PT, UK. Electronic address: clair.baldock@manchester.ac.uk.
authors.forename: Clair
authors.initials: C
authors.lastname: Baldock
mesh_terms: D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D002460:Cell Line; D006023:Glycoproteins / Q000737:chemistry; D057809:HEK293 Cells; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000737:chemistry; D051379:Mice; D008958:Models, Molecular; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D054730:Protein Interaction Domains and Motifs; D020836:Protein Structure, Quaternary; D011506:Proteins / Q000737:chemistry* / Q000502:physiology; D053838:Scattering, Small Angle; D015398:Signal Transduction; D014961:X-Ray Diffraction
chemical_list: D019485:Bone Morphogenetic Proteins; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D011506:Proteins; C576635:TWSG1 protein, human; C054234:chordin
keywords: BMP signalling; Chordin; Tolloid proteinase; Twisted gastrulation
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