缓步动物热溶性蛋白的独有特性及其在极端环境适应中的功能

Tardigrade Heat-soluble Proteins:Unique Properties and Biological Functions in The Survival of Extreme Environment

缓步动物(tardigrades,俗称水熊虫)等一些低等动物可在干燥、低温、低压等极端条件下长期生存。这种超常的生存能力依赖于细胞在大幅度脱水后,进入一种叫做隐生(cryptobiosis)的特殊状态,使细胞脱水、身体萎缩并停止新陈代谢,从而可以允许动物在极端条件下生存多年。当环境好转时,处于隐生状态的细胞或者身体又可以再次吸收水份进行复苏。缓步动物中有着多种独特的内在无序蛋白质(intrinsic disorder protein),统称为热溶性蛋白质。这些热溶性蛋白质在细胞脱水过程中构象发生重要变化,可对液态水进行固定,从而起到了重要的细胞保护作用。对此类蛋白质的性质研究尚处于初期阶段,缺乏深入的机理性研究。本文简要总结了缓步动物中特有热溶性蛋白质的序列特征、理化性质,及其潜在的生物功能与机制。同时讨论了这些热溶性蛋白质在高等动物细胞对低温、低氧等极端环境适应中的可能应用。人类细胞在极端环境中的隐生和可逆复苏,将在医学领域和未来宇宙探索与星际移民中有极其重要的用途。

Tardigrades,also known as water bears,possess an extraordinary ability to survive for extended periods under harsh conditions like extreme dryness,low temperatures,and low pressure.Under such condition,tardigrades enter into a state of cryptobiosis,where they undergo dehydration,body shrinkage,and metabolic halting,enabling them to endure extreme conditions for years.Once the environment improves,the cells or body in cryptobiosis can rehydrate and recover.Tardigrades owe this ability in part to some unique tardigrade disordered proteins(TDP),also called heat-soluble proteins,which safeguard their cells during dehydration by reshaping their structure to fix liquid water during desiccation.However,research on these proteins is still in its nascent stages,and the thorough mechanistic investigations are lacking.This article provides a concise overview of these unique proteins found in tardigrades,including their sequence,physicochemical properties,potential biological functions,and mechanisms.Currently,there are 3 major families of TDPs known as cytosolic-abundant heat-soluble proteins(CAHS),secretory-abundant heat-soluble proteins(SAHS),and mitochondrial-abundant heat-soluble proteins(MAHS).A large fraction of these proteins contain are intrinsic disorder regions that are critical to their function in desiccation tolerance.The CAHS proteins contain a longα-helix and two flanking intrinsic disordered regions,and play roles in the vitrification process during desiccation.The SAHS proteins contain a centralβ-barrel and a helix-turn-helix“cap”motif,and they may form a protective network outside the cells under extreme environment.The MAHS proteins contain a loosely organized“core”consist of 5α-helix and the flanking region of disordered motifs,and their major roles is to protect the mitochondrial during desiccation.The unique structure and property of these TDPs may help to develop new technology in aiding higher animals to adapt to extreme environments,such as low temperatures and low oxygen.The ability of human cells to undergo cryptobiosis and reversible recovery in extreme environments has critical implications in fields like medicine,space exploration,and interstellar immigration.