Ren Chang, Zheng Yongxin, Liu Chunlan, Mencius Jun, Wu Zhili, Quan Shu
State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai Collaborative Innovation Center for Biomanufacturing (SCICB), Shanghai 200237, China.
State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai Collaborative Innovation Center for Biomanufacturing (SCICB), Shanghai 200237, China; Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, Shanghai 200237, China.
J Mol Biol. 2022 Mar 15;434(5):167405. doi: 10.1016/j.jmb.2021.167405. Epub 2021 Dec 13.
Molecular chaperones are diverse biomacromolecules involved in the maintenance of cellular protein homeostasis (proteostasis). Here we demonstrate that in contrast to most chaperones with defined three-dimensional structures, the acid-inducible protein Asr in Escherichia coli is intrinsically disordered and exhibits varied aggregation-preventing or aggregation-promoting activities, acting as a "conditionally active chaperone". Bioinformatics and experimental analyses of Asr showed that it is devoid of hydrophobic patches but rich in positive charges and local polyproline II backbone structures. Asr contributes to the integrity of the bacterial outer membrane under mildly acidic conditions in vivo and possesses chaperone activities toward model clients in vitro. Notably, its chaperone activity is dependent on the net charges of clients: on the one hand, it inhibits the aggregation of clients with similar net charges; on the other hand, it stimulates the aggregation of clients with opposite net charges. Mutational analysis confirmed that positively charged residues in Asr are essential for the varied effects on protein aggregation, suggesting that electrostatic interactions are the major driving forces underlying Asr's proteostasis-related activity. These findings present a unique example of an intrinsically disordered molecular chaperone with distinctive dual functions-as an aggregase or as a chaperone-depending on the net charges of clients.
分子伴侣是参与维持细胞蛋白质稳态（蛋白质平衡）的多种生物大分子。在这里，我们证明，与大多数具有确定三维结构的伴侣蛋白不同，大肠杆菌中的酸诱导蛋白Asr是内在无序的，并且表现出不同的防止聚集或促进聚集的活性，充当“条件活性伴侣蛋白”。对Asr的生物信息学和实验分析表明，它没有疏水斑块，但富含正电荷和局部多聚脯氨酸II主链结构。Asr在体内轻度酸性条件下有助于细菌外膜的完整性，并在体外对模型客户具有伴侣活性。值得注意的是，其伴侣活性取决于客户的净电荷：一方面，它抑制具有相似净电荷的客户聚集；另一方面，它刺激具有相反净电荷的客户聚集。突变分析证实，Asr中的带正电荷残基对于对蛋白质聚集的不同影响至关重要，这表明静电相互作用是Asr与蛋白质平衡相关活性的主要驱动力。这些发现提供了一个独特的例子，即一种内在无序的分子伴侣具有独特的双重功能——作为聚集酶或作为伴侣，这取决于客户的净电荷。
