Abstract：
Heat shock factor 1 (HSF1) primarily regulates various cellular stress responses. Previous studies have shown that low pH within the physiological range directly activates HSF1 function in vitro. However, the detailed molecular mechanisms remain unclear. This study proposes a molecular mechanism based on the trimerization behavior of HSF1 at different pH values. Extensive mutagenesis of human and goldfish HSF1 revealed that the optimal pH for trimerization depended on the identity of residue 103. In particular, when residue 103 was occupied by tyrosine, a significant increase in the optimal pH was observed, regardless of the rest of the sequence. This behavior can be explained by the protonation state of the neighboring histidine residues, His101 and His110. Residue 103 plays a key role in trimerization by forming disulfide or non-covalent bonds with Cys36. If tyrosine resides at residue 103 in an acidic environment, its electrostatic interactions with positively charged histidine residues prevent effective trimerization. His101 and His110 are neutralized at a higher pH, which releases Tyr103 to interact with Cys36 and drives the effective trimerization of HSF1. This study showed that the protonation state of a histidine residue can regulate the intramolecular interactions, which consequently leads to a drastic change in the oligomerization behavior of the entire protein.
摘要：
热休克因子1（HSF1）主要调节各种细胞应激反应。先前的研究表明，生理范围内的低pH值直接在体外激活HSF1功能。然而,详细的分子机制尚不清楚.本研究提出了基于HSF1在不同pH值下的三聚行为的分子机理。人类和金鱼HSF1的广泛诱变表明，三聚的最佳pH值取决于残基103的身份。特别是,当残基103被酪氨酸占据时，观察到最佳pH值显着增加，不管序列的其余部分。这种行为可以通过相邻组氨酸残基的质子化状态来解释，His101和His110。残基103通过与Cys36形成二硫键或非共价键在三聚中起关键作用。如果酪氨酸在酸性环境中位于残基103，其与带正电荷的组氨酸残基的静电相互作用阻止有效的三聚。His101和His110在较高的pH值下被中和，它释放Tyr103与Cys36相互作用，并驱动HSF1的有效三聚。这项研究表明，组氨酸残基的质子化状态可以调节分子内相互作用，这因此导致整个蛋白质的寡聚化行为的急剧变化。
