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STATs dimerize in the absence of phosphorylation
Jutta Braunstein1, Siska Brutsaert, Rich Olson
1Department of Microbiology, Columbia University, New York, New York 10032, USA.
The Journal of Biological Chemistry
|July 2, 2003
Summary
Signal transducer and activator of transcription (STAT) proteins, Stat1 and Stat3, exist as stable homodimers even before activation. This pre-formed dimeric structure is observed in both inactive recombinant proteins and unstimulated cellular STATs.
Area of Science:
- Molecular Biology
- Cell Signaling
- Protein Structure
Background:
- Signal transducer and activator of transcription (STAT) proteins are key transcription factors activated by tyrosine kinases.
- STAT dimerization is crucial for nuclear translocation and DNA binding upon activation.
- Existing crystal structures of activated STATs offer limited insight into the dynamic regulation of STAT activity.
Purpose of the Study:
- To investigate the structural changes in Stat1 and Stat3 during activation.
- To explore the quaternary structure of inactive and unstimulated STAT proteins.
Main Methods:
- Preparation of full-length inactive recombinant Stat1 and Stat3 proteins.
- Analysis of STAT protein structure in unstimulated cells.
- Structural studies focusing on STAT dimerization.
Main Results:
- Inactive recombinant Stat1 and Stat3 proteins exist as stable homodimers, despite being unable to bind DNA.
- STAT1 and STAT3 proteins in the cytoplasm of unstimulated cells also exhibit a dimeric structure.
- These findings reveal a pre-activation dimeric state for Stat1 and Stat3.
Conclusions:
- Stat1 and Stat3 exist as stable homodimers prior to tyrosine kinase-mediated activation.
- The pre-formed dimeric structure is a characteristic of STAT proteins in their inactive state.
- This suggests that STAT dimerization is not solely a consequence of activation but a pre-existing condition.