Crystal Structure of Tetrameric Arabidopsis MYC2 Reveals the Mechanism of Enhanced Interaction with DNA

Publication date: 16 May 2017
Source:Cell Reports, Volume 19, Issue 7
Author(s): Teng-fei Lian, Yong-ping Xu, Lan-fen Li, Xiao-Dong Su
Jasmonates (JAs) are essential plant hormones that play important roles in the regulation of plant growth and the response to environmental stress. In the JA signaling pathway, the core transcription factors are a class of basic helix-loop-helix (bHLH) proteins, including MYC2, MYC3, and MYC4, that have different regulatory capacities. Here, we report the 2.7 Å crystal structure of the MYC2 bHLH domain complexed with G-box DNA, showing a cis-tetrameric structure. Biochemical assays confirmed that full-length MYC2 forms a stable homo-tetramer both in solution and in DNA-bound states, whereas MYC3 forms only a homodimer. Isothermal titration calorimetry (ITC) assays demonstrated that tetramerization enhanced DNA binding affinity, and fluorescence resonance energy transfer (FRET) assay indicated DNA looping potential of tetrameric MYC2. Luciferase assay further confirmed the importance of tetramerization in transcriptional regulation. Our studies provide a mechanistic explanation for the regulatory differences of MYC transcription factors.

Graphical abstract

Teaser

Lian et al. solved the crystal structure of the Arabidopsis transcription factor MYC2-DNA complex and showed that MYC2 and MYC3 exist as homotetramer and homodimer in solution, respectively, explaining the different regulatory capacities of these bHLH transcription factors.


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