title: DNA binding reduces the dissociation rate of STAT1 dimers and impairs the interdimeric exchange of protomers.
abstract: BACKGROUND
  A shift between two dimer conformations has been proposed for the transcription factor STAT1 (signal transducer and activator of transcription 1) which links DNA binding of the parallel dimer to tyrosine dephosphorylation of the antiparallel dimer as two consecutive and important steps in interferon- γ (IFNγ)-mediated signalling. However, neither the kinetics nor the molecular mechanisms involved in this conformational transition have been determined so far.
  
  
  RESULTS
  Our results demonstrated that the dissociation of dimers into monomers and their subsequent re-association into newly formed tyrosine-phosphorylated dimers is a relatively slow process as compared to the fast release from high-affinity DNA-binding sites, termed GAS (gamma-activated sequence). In addition, we noted an inhibitory effect of GAS binding on the exchange rate of protomers, indicating that DNA binding substantially impedes the recombination of dimeric STAT1. Furthermore, we found that reciprocal aminoterminal interactions between two STAT1 molecules are not required for the interchange of protomers, as an oligomerization-deficient point mutant displayed similar interdimeric exchange kinetics as the wild-type molecule.
  
  
  CONCLUSIONS
  Our results demonstrate that DNA binding impairs the oscillation rate between STAT1 conformers. Furthermore, these data suggest that the rapid release from high-affinity GAS sites is not a rate-limiting step in IFNγ-mediated signal transduction. Further investigations are needed to decipher the physiological significance of the observed dissociation/re-association process of STAT1 dimers.
authors.affiliation: Klinik für Psychosomatische Medizin und Psychotherapie, Georg-August-Universität Göttingen, Waldweg 33, 37073, Göttingen, Germany. theresa.riebeling@med.uni-goettingen.de.
authors.forename: Theresa
authors.initials: T
authors.lastname: Riebeling
authors.affiliation: Klinik für Psychosomatische Medizin und Psychotherapie, Georg-August-Universität Göttingen, Waldweg 33, 37073, Göttingen, Germany. julia.staab@med.uni-goettingen.de.
authors.forename: Julia
authors.initials: J
authors.lastname: Staab
authors.affiliation: Klinik für Psychosomatische Medizin und Psychotherapie, Georg-August-Universität Göttingen, Waldweg 33, 37073, Göttingen, Germany. cherrma@gwdg.de.
authors.forename: Christoph
authors.initials: C
authors.lastname: Herrmann-Lingen
authors.affiliation: Klinik für Psychosomatische Medizin und Psychotherapie, Georg-August-Universität Göttingen, Waldweg 33, 37073, Göttingen, Germany. thomas.meyer@med.uni-goettingen.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Meyer
mesh_terms: D002460:Cell Line; D004247:DNA / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D011485:Protein Binding; D055503:Protein Multimerization; D055550:Protein Stability; D021122:Protein Subunits / Q000737:chemistry*; D050794:STAT1 Transcription Factor / Q000737:chemistry*
chemical_list: D021122:Protein Subunits; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D004247:DNA