State Key Laboratory of Agrobiotechnology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
The Hospital for Sick Children Research Institute, Toronto, Canada.
Nat Commun. 2021 May 21;12(1):3007. doi: 10.1038/s41467-021-23338-y.
Small heat shock proteins (sHsps) bind unfolding proteins, thereby playing a pivotal role in the maintenance of proteostasis in virtually all living organisms. Structural elucidation of sHsp-substrate complexes has been hampered by the transient and heterogeneous nature of their interactions, and the precise mechanisms underlying substrate recognition, promiscuity, and chaperone activity of sHsps remain unclear. Here we show the formation of a stable complex between Arabidopsis thaliana plastid sHsp, Hsp21, and its natural substrate 1-deoxy-D-xylulose 5-phosphate synthase (DXPS) under heat stress, and report cryo-electron microscopy structures of Hsp21, DXPS and Hsp21-DXPS complex at near-atomic resolution. Monomeric Hsp21 binds across the dimer interface of DXPS and engages in multivalent interactions by recognizing highly dynamic structural elements in DXPS. Hsp21 partly unfolds its central α-crystallin domain to facilitate binding of DXPS, which preserves a native-like structure. This mode of interaction suggests a mechanism of sHsps anti-aggregation activity towards a broad range of substrates.
小分子热休克蛋白 (sHsps) 结合变性蛋白，从而在几乎所有生物体中对维持蛋白质平衡发挥关键作用。sHsp-底物复合物的结构阐明受到其相互作用的瞬时性和异质性的阻碍，并且 sHsps 底物识别、混杂性和分子伴侣活性的精确机制仍不清楚。在这里，我们展示了在热应激下拟南芥质体 sHsp、Hsp21 与其天然底物 1-脱氧-D-木酮糖 5-磷酸合酶 (DXPS) 之间形成稳定复合物，并报告了 Hsp21、DXPS 和 Hsp21-DXPS 复合物在近原子分辨率下的冷冻电子显微镜结构。单体 Hsp21 横跨 DXPS 的二聚体界面结合，并通过识别 DXPS 中高度动态的结构元件进行多价相互作用。Hsp21 部分展开其中心 α-晶体结构域以促进 DXPS 的结合，从而保持类似天然的结构。这种相互作用模式表明了 sHsps 对广泛的底物的抗聚集活性的一种机制。
