Institute for Advanced Biosciences, Keio University, Nihonkoku, 403-1, Daihouji, Tsuruoka, Yamagata, 997-0017, Japan.
Systems Biology Program, Graduate School of Media and Governance, Keio University, 5322 Endo, Fujisawa, Kanagawa, 252-0882, Japan.
BMC Genomics. 2022 May 28;23(1):405. doi: 10.1186/s12864-022-08642-1.
Tardigrades are microscopic animals that are capable of tolerating extreme environments by entering a desiccated state of suspended animation known as anhydrobiosis. While antioxidative stress proteins, antiapoptotic pathways and tardigrade-specific intrinsically disordered proteins have been implicated in the anhydrobiotic machinery, conservation of these mechanisms is not universal within the phylum Tardigrada, suggesting the existence of overlooked components.
Here, we show that a novel Mn-dependent peroxidase is an important factor in tardigrade anhydrobiosis. Through time-series transcriptome analysis of Ramazzottius varieornatus specimens exposed to ultraviolet light and comparison with anhydrobiosis entry, we first identified several novel gene families without similarity to existing sequences that are induced rapidly after stress exposure. Among these, a single gene family with multiple orthologs that is highly conserved within the phylum Tardigrada and enhances oxidative stress tolerance when expressed in human cells was identified. Crystallographic study of this protein suggested Zn or Mn binding at the active site, and we further confirmed that this protein has Mn-dependent peroxidase activity in vitro.
Our results demonstrated novel mechanisms for coping with oxidative stress that may be a fundamental mechanism of anhydrobiosis in tardigrades. Furthermore, localization of these sets of proteins mainly in the Golgi apparatus suggests an indispensable role of the Golgi stress response in desiccation tolerance.
水熊虫是一种能够通过进入干燥的休眠状态来耐受极端环境的微小动物，这种休眠状态被称为脱水休眠。虽然抗氧化应激蛋白、抗细胞凋亡途径和水熊虫特异性的无规卷曲结构蛋白已被牵涉到脱水休眠机制中，但这些机制在缓步动物门中并不普遍存在，这表明存在被忽视的成分。
在这里，我们表明一种新型的 Mn 依赖性过氧化物酶是水熊虫脱水休眠的一个重要因素。通过对暴露在紫外线下的 Ramazzottius varieornatus 标本进行时间序列转录组分析，并与进入脱水休眠进行比较，我们首先鉴定了几个没有与现有序列相似性的新基因家族，这些基因家族在受到压力后迅速被诱导。在这些基因家族中，鉴定出了一个单一的基因家族，该家族具有多个在缓步动物门中高度保守的同源基因，并且当在人类细胞中表达时可以增强对氧化应激的耐受性。该蛋白的晶体学研究表明其活性位点具有 Zn 或 Mn 结合，我们进一步证实该蛋白在体外具有 Mn 依赖性过氧化物酶活性。
我们的研究结果表明了一种应对氧化应激的新机制，这可能是水熊虫脱水休眠的基本机制。此外，这些蛋白的定位主要在高尔基体中，这表明高尔基体应激反应在干燥耐受性中起着不可或缺的作用。
