title: Structural characterization of unphosphorylated STAT5a oligomerization equilibrium in solution by small-angle X-ray scattering.
abstract: Signal transducer and activator of transcription (STAT) proteins play a crucial role in the activation of gene transcription in response to extracellular stimuli. The regulation and activity of these proteins require a complex rearrangement of the domains. According to the established models, based on crystallographic data, STATs convert from a basal antiparallel inactive dimer into a parallel active one following phosphorylation. The simultaneous analysis of small-angle X-ray scattering data measured at different concentrations of unphosphorylated human STAT5a core domain unambiguously identifies the simultaneous presence of a monomer and a dimer. The dimer is the minor species but could be structurally characterized by SAXS in the presence of the monomer using appropriate computational tools and shown to correspond to the antiparallel assembly. The equilibrium is governed by a moderate dissociation constant of K(d) approximately 90 microM. Integration of these results with previous knowledge of the N-terminal domain structure and dissociation constants allows the modeling of the full-length protein. A complex network of intermolecular interactions of low or medium affinity is suggested. These contacts can be eventually formed or broken to trigger the dramatic modifications in the dimeric arrangement needed for STAT regulation and activity.
authors.affiliation: Laboratory of Biomolecular NMR, Institute for Research in Biomedicine, Parc Científic de Barcelona, Baldiri Reixac, 10-12, 08028 Barcelona, Spain. pau.bernado@irbbarcelona.org
authors.forename: Pau
authors.initials: P
authors.lastname: Bernadó
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Pérez
authors.forename: Jascha
authors.initials: J
authors.lastname: Blobel
authors.forename: Juan
authors.initials: J
authors.lastname: Fernández-Recio
authors.forename: Dmitri I
authors.initials: DI
authors.lastname: Svergun
authors.forename: Miquel
authors.initials: M
authors.lastname: Pons
mesh_terms: D003198:Computer Simulation; D006801:Humans; D010766:Phosphorylation; D011487:Protein Conformation; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D050799:STAT5 Transcription Factor / Q000737:chemistry* / Q000378:metabolism; D053838:Scattering, Small Angle; D025521:Tumor Suppressor Proteins / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; D025521:Tumor Suppressor Proteins