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The Mad1-Sin3B interaction involves a novel helical fold
C A Spronk1, M Tessari, A M Kaan
1Department of Biophysical Chemistry, NSR Center, University of Nijmegen, The Netherlands.
Abstract:
Sin3A or Sin3B are components of a corepressor complex that mediates repression by transcription factors such as the helix-loop-helix proteins Mad and Mxi. Members of the Mad/Mxi family of repressors play important roles in the transition between proliferation and differentiation by down-regulating the expression of genes that are activated by the proto-oncogene product Myc. Here, we report the solution structure of the second paired amphipathic helix (PAH) domain (PAH2) of Sin3B in complex with a peptide comprising the N-terminal region of Mad1. This complex exhibits a novel interaction fold for which we propose the name 'wedged helical bundle'. Four alpha-helices of PAH2 form a hydrophobic cleft that accommodates an amphipathic Mad1 alpha-helix. Our data further show that, upon binding Mad1, secondary structure elements of PAH2 are stabilized. The PAH2-Mad1 structure provides the basis for determining the principles of protein interaction and selectivity involving PAH domains.
Insights
Researchers determined the structure of a Sin3B protein complex with Mad1. This reveals a novel
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- Sin3A/Sin3B proteins form corepressor complexes regulating gene expression.
- Mad/Mxi repressors are crucial for cell proliferation and differentiation.
- These repressors down-regulate genes activated by the Myc proto-oncogene.
Purpose of the Study:
- To determine the solution structure of the Sin3B PAH2 domain in complex with a Mad1 peptide.
- To elucidate the interaction mechanism between Sin3B and Mad1.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy to determine the solution structure.
- Peptide-protein complex analysis.
Main Results:
- The structure of the Sin3B PAH2 domain bound to a Mad1 peptide was solved.
- A novel 'wedged helical bundle' interaction fold was identified.
- Four alpha-helices in PAH2 create a hydrophobic cleft accommodating the Mad1 helix.
- Binding of Mad1 stabilizes secondary structure elements within PAH2.
Conclusions:
- The determined PAH2-Mad1 structure provides insights into protein interaction principles.
- This structure is key to understanding the selectivity of paired amphipathic helix (PAH) domain interactions.
- The findings contribute to understanding gene regulation by corepressor complexes.