The enigmatic LEA proteins and other hydrophilins
The enigmatic LEA proteins and other hydrophilins
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DOI：
10.1104/pp.108.120725
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发表时间：
2008-09-01
期刊：
影响因子：
7.4
通讯作者：
Covarrubias, Alejandra A.
中科院分区：
文献类型：
--
作者：
Battaglia, Marina;Olvera-Carrillo, Yadira;Covarrubias, Alejandra A.
水分限制影响所有类型的生物在其生命周期的某个阶段；因此，通过进化选择了许多策略来应对水分不足，包括酶活性和基因表达的变化等。在植物中，一组非常亲水的蛋白质，被称为晚期胚胎发育（LATE EMBRYOGENESIS ABUNDANT， LEA）蛋白，在种子成熟的最后阶段（当胚胎获得干燥耐受性时）和营养器官的水分亏缺期间积累到高水平，表明在水分限制期间具有保护作用（Dure, 1993b; Bray, 1997； Garay-Arroyo等，2000；Hoekstra等，2001）。LEA蛋白根据序列相似性被分为不同的科（见下文；Dure等人，1989；Ingram和Bartels, 1996； Colmenero-Flores等人，1999;Cuming, 1999）。虽然不同科的成员之间没有明显的相似性，但它们大多数的一个统一和突出的特征是它们的高亲水性和高含量的甘氨酸和小氨基酸，如Ala和Ser （Baker et al., 1988; Dure, 1993b）。大多数LEA蛋白是一种更广泛的被称为“亲水蛋白”的蛋白质群的一部分。“定义这组蛋白质的物理化学特征是Gly含量大于6%，亲水性指数大于1。通过数据库搜索发现，该标准选择了大部分LEA蛋白，以及来自不同分类群的额外蛋白（Garay-Arroyo et al., 2000）。大肠杆菌和酿酒酵母的基因组中分别含有5个和12个编码亲水蛋白特征的基因。所有这些基因的转录本在对渗透胁迫的反应中积累的事实表明，亲水蛋白代表了对水分缺乏的广泛适应（Garay-Arroyo等人，2000；Posas等人，2000；Yale和Bohnert, 2001；酵菌基因组数据库项目，http://www）。yeastgenome。org)。值得注意的是，现在已知这些蛋白质分布在原始、真细菌和真核生物结构域，这将在本综述的后面描述。尽管亲水蛋白的功能作用仍是推测性的，但有证据支持它们参与适应和/或对压力的适应性反应。一些植物亲水性蛋白（LEA蛋白）在植物和酵母中的异位表达赋予植物对缺水条件的耐寒性（Imai等，1996；Xu等，1996；Swire-Clark和Marcotte, 1999； Zhang等，2000），它们的存在与抗寒性有关（Danyluk等，1994,1998；Ismail等，1999a, 1999b； Puhakainen等，2004a； Nakayama等，2007）。渗透敏感表型是由大肠杆菌中RMF亲水性基因的缺失（Garay-Arroyo et al., 2000）和苔藓小壶菌（Physcomitrella patens）中LEA蛋白的缺失引起的（Saavedra et al., 2006）。为了进一步了解它们的功能，已经建立了类似于用于测试其他保护分子（如伴侣分子）作用的体外分析方法。其中的例子是冷冻保护试验，其中LEA蛋白的保护作用是使用冷冻不稳定酶来测试的（Lin和Thomashow， 1992）。在脱水试验中，苹果酸脱氢酶和乳酸脱氢酶（LDH）的活性在假设的保护蛋白存在或不存在的情况下被测量，结果表明来自植物、细菌和酵母的亲水蛋白能够保护它们的酶活性。在类似的条件下，海藻糖需要比亲水性多105倍的摩尔量才能对LDH产生相同的保护作用，这表明海藻糖具有保护作用。
Water limitation affects all types of organisms at some stage during their life cycle; therefore, many strategies have been selected through evolution to cope with water deficit, including changes in enzyme activities and in gene expression, among others. In plants, a group of very hydrophilic proteins, known as LATE EMBRYOGENESIS ABUNDANT (LEA) proteins, accumulate to high levels during the last stage of seed maturation (when acquisition of desiccation tolerance occurs in the embryo) and during water deficit in vegetative organs, suggesting a protective role during water limitation (Dure, 1993b; Bray, 1997; Garay-Arroyo et al., 2000; Hoekstra et al., 2001). LEA proteins have been grouped into various families on the basis of sequence similarity (see below; Dure et al., 1989; Ingram and Bartels, 1996; Colmenero-Flores et al., 1999; Cuming, 1999). Although significant similarity has not been detected between the members of the different families, a unifying and outstanding feature of most of them is their high hydrophilicity and high content of Gly and small amino acids like Ala and Ser (Baker et al., 1988; Dure, 1993b). Most LEA proteins are part of a more widespread group of proteins called ‘‘hydrophilins.’’The physicochemical characteristics that define this set of proteins are a Gly content greater than 6% and a hydrophilicity index greater than 1. By database searching, it was shown that this criterion selects most LEA proteins, as well as additional proteins from different taxa (Garay-Arroyo et al., 2000). The genomes of Escherichia coli and Saccharomyces cerevisiae contain five and 12 genes, respectively, encoding proteins with the characteristics of hydrophilins. The fact that the transcripts of all these genes accumulate in response to osmotic stress suggests that hydrophilins represent a widespread adaptation to water deficit (Garay-Arroyo et al., 2000; Posas et al., 2000; Yale and Bohnert, 2001; Saccharomyces Genome Database project, http://www. yeastgenome. org). Remarkably, now it is known that these proteins are distributed across archeal, eubacterial, and eukaryotic domains, as will be described later in this review.Although the functional role of hydrophilins remains speculative, there is evidence supporting their participation in acclimation and/or in the adaptive response to stress. Ectopic expression of some plant hydrophilins (LEA proteins) in plants and yeast confers tolerance to water-deficit conditions (Imai et al., 1996; Xu et al., 1996; Swire-Clark and Marcotte, 1999; Zhang et al., 2000), and their presence has been associated with chilling tolerance (Danyluk et al., 1994, 1998; Ismail et al., 1999a, 1999b; Puhakainen et al., 2004a; Nakayama et al., 2007). An osmosensitive phenotype is caused by the deletion of the RMF hydrophilin gene in E. coli (Garay-Arroyo et al., 2000) and by the absence of a LEA protein in the moss Physcomitrella patens (Saavedra et al., 2006). To gain further insight into their function, in vitro assays have been established similar to those used to test the role of other protective molecules such as chaperones. Examples of these are cryoprotection assays, in which the protective role of LEA proteins is tested using freeze-labile enzymes (Lin and Thomashow, 1992). Dehydration assays, in which the activities of malate dehydrogenase and lactate dehydrogenase (LDH) were measured in the presence or absence of a putative protecting protein, showed that hydrophilins from plants, bacteria, and yeast were able to protect their enzymatic activity. Under similar conditions, trehalose was required in a 105-fold molar excess over hydrophilins to confer the same protective level to LDH, suggesting that they confer protection …