The MYB4 transcription factor, a member of R2R3-type subfamily of MYB domain protein, plays a key role in the regulation of accumulation of UV-B absorbing phenylpropanoids in Arabidopsis. Although UV-B and thermal stress generate some common stress response, the effect of elevated temperature on the conformational stability of MYB4 remains limited. This study describes the folding and aggregation properties of Arabidopsis MYB4 protein under thermal stress condition. Circular dichroism spectral studies and Bis-ANS binding assays have indicated that the removal of the N-terminal MYB domain affects the structural conformation of the protein and disrupts surface hydrophobic binding sites at higher temperature. Urea-induced equilibrium unfolding studies revealed that the removal of the N-terminal region lowers the thermodynamic stability of MYB4 at elevated temperature. Tryptophan fluorescence spectral pattern and both in vitro and in vivo aggregation studies have revealed the importance of the N-terminal second MYB domain encompassing the N-terminal 62-116 amino acid residues in regulating MYB4 protein stability at higher temperature. On the other hand, comparison of the growth response of wild-type Arabidopsis and atmyb4 mutant line have suggested that MYB4 may not directly affect plant response under thermal stress condition and only marginal role of MYB4 in controlling thermomorphogenesis in Arabidopsis . Interestingly, immunoprecipitation studies have revealed that HSP90 specifically interacts with MYB4 in vivo at the endogenous level, indicating the possible role of HSP90 in governing the stability of MYB4 at elevated temperature in Arabidopsis.

中文翻译：

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N-末端 MYB 结构域影响热应激下拟南芥 MYB4 转录因子的稳定性和折叠方面

MYB4 转录因子是 MYB 结构域蛋白的 R2R3 型亚家族的成员，在拟南芥中吸收 UV-B 的苯丙烷类化合物的积累调控中起关键作用。尽管 UV-B 和热应力会产生一些常见的应力响应，但高温对 MYB4 构象稳定性的影响仍然有限。本研究描述了拟南芥 MYB4 蛋白在热应激条件下的折叠和聚集特性。圆二色性光谱研究和 Bis-ANS 结合测定表明，去除 N 端 MYB 结构域会影响蛋白质的结构构象，并在较高温度下破坏表面疏水结合位点。尿素诱导的平衡解折叠研究表明，去除 N 端区域会降低 MYB4 在高温下的热力学稳定性。色氨酸荧光光谱模式以及体外和体内聚集研究揭示了包含 N 端 62-116 个氨基酸残基的 N 端第二个 MYB 结构域在较高温度下调节 MYB4 蛋白稳定性的重要性。另一方面，野生型拟南芥和 atmyb4 突变株系的生长反应的比较表明，MYB4 可能不会直接影响热胁迫条件下的植物反应，并且 MYB4 在控制拟南芥的热形态发生方面仅起边缘作用。有趣的是，免疫沉淀研究表明 HSP90 在内源性水平上与体内 MYB4 特异性相互作用，