Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Commun Biol. 2023 Jan 30;6(1):121. doi: 10.1038/s42003-023-04512-y.
Small heat shock proteins (sHSPs) are chaperones with well-characterized roles in heat stress, but potential roles for sHSPs in desiccation tolerance have not been as thoroughly explored. We identified nine sHSPs from the tardigrade Hypsibius exemplaris, each containing a conserved alpha-crystallin domain flanked by disordered regions. Many of these sHSPs are highly expressed. Multiple tardigrade and human sHSPs could improve desiccation tolerance of E. coli, suggesting that the capacity to contribute to desicco-protection is a conserved property of some sHSPs. Purification and subsequent analysis of two tardigrade sHSPs, HSP21 and HSP24.6, revealed that these proteins can oligomerize in vitro. These proteins limited heat-induced aggregation of the model enzyme citrate synthase. Heterologous expression of HSP24.6 improved bacterial heat shock survival, and the protein significantly reduced heat-induced aggregation of soluble bacterial protein. Thus, HSP24.6 likely chaperones against protein aggregation to promote heat tolerance. Furthermore, HSP21 and HSP24.6 limited desiccation-induced aggregation and loss of function of citrate synthase. This suggests a mechanism by which tardigrade sHSPs promote desiccation tolerance, by limiting desiccation-induced protein aggregation, thereby maintaining proteostasis and supporting survival. These results suggest that sHSPs provide a mechanism of general stress resistance that can also be deployed to support survival during anhydrobiosis.
小型热休克蛋白 (sHSPs) 是在热应激中具有明确作用的伴侣蛋白，但 sHSPs 在干燥耐受性中的潜在作用尚未得到充分探索。我们从缓步动物 Hypsibius exemplaris 中鉴定出 9 种 sHSPs，每种 sHSP 都含有保守的α-晶状体结构域，两侧为无序区域。其中许多 sHSPs 高度表达。多种缓步动物和人类 sHSPs 可以提高大肠杆菌的干燥耐受性，这表明有助于干燥保护的能力是一些 sHSPs 的保守特性。两种缓步动物 sHSPs（HSP21 和 HSP24.6）的纯化和随后分析表明，这些蛋白质可以在体外寡聚化。这些蛋白质限制了模型酶柠檬酸合酶的热诱导聚集。HSP24.6 的异源表达提高了细菌的热休克存活率，并且该蛋白显著减少了热诱导的可溶性细菌蛋白聚集。因此，HSP24.6 可能通过伴侣蛋白防止蛋白质聚集来促进耐热性。此外，HSP21 和 HSP24.6 限制了柠檬酸合酶的干燥诱导聚集和功能丧失。这表明了缓步动物 sHSPs 促进干燥耐受性的一种机制，即通过限制干燥诱导的蛋白质聚集，从而维持蛋白质平衡并支持生存。这些结果表明，sHSPs 提供了一种普遍的应激抗性机制，也可以用于在脱水休眠期间支持生存。
