Schmitz Johanna, Tierbach Alena, Lenz Henning, Meschenmoser Karoline, Knoop Volker
IZMB - Institut für Zelluläre und Molekulare Botanik, Abteilung Molekulare Evolution, Universität Bonn, Kirschallee 1, D-53115 Bonn, Germany.
Biochim Biophys Acta. 2013 Sep;1828(9):2032-40. doi: 10.1016/j.bbamem.2013.05.019. Epub 2013 May 31.
Membrane proteins of the Arabidopsis thaliana MRS2 (MGT) family have been characterised as magnesium transporters. Like their bacterial CorA homologues, the plant MRS2 proteins are characterised by an invariable GMN tripeptide motif terminating the first of two closely spaced transmembrane domains at the carboxy-termini. The functional Mg(2+) transport channel is assembled as a pentamer in the case of CorA. However, in contrast to the single CorA genes of bacteria, plant genomes encode up to 10 highly divergent MRS2 proteins. To elucidate structure-function relationships and the possibility of plant MRS2 hetero-pentamer formation, we performed protein-protein interaction studies in the yeast mating-based split-ubiquitin system (mbSUS) and concomitant protein modelling using I-TASSER. Despite very restricted sequence similarities and variable polypeptide insertions all AtMRS2 proteins feature the key structural elements determined for the CorA crystal structure. The mbSUS setup conclusively demonstrates protein-protein interactions of any given AtMRS2 protein not only with itself but also highly permissive interactions to varying degrees among all AtMRS2 proteins. AtMRS2-3 seems particularly prone to non-selective, strong interactions with the other homologues. Deletion constructs show that six amino acids may be deleted from the carboxy-terminus and 27 (but not 41) from the amino-terminus of AtMRS2-7 without impairment of homologous or heterologous protein interactions. Despite significant diversification, the plant MRS2 proteins have obviously retained an ancient CorA/MRS2 core structure and the capacity for protein-protein interactions. Plant magnesium homeostasis may be influenced by hetero-oligomer channel formation where different plant MRS2 proteins meet in the same membrane naturally or in transgenic approaches.
拟南芥MRS2（MGT）家族的膜蛋白已被鉴定为镁转运体。与它们的细菌CorA同源物一样，植物MRS2蛋白的特征是在羧基末端两个紧密间隔的跨膜结构域中的第一个的末端有一个不变的GMN三肽基序。在CorA的情况下，功能性Mg(2+)转运通道组装成五聚体。然而，与细菌的单个CorA基因不同，植物基因组编码多达10种高度不同的MRS2蛋白。为了阐明结构-功能关系以及植物MRS2异源五聚体形成的可能性，我们在基于酵母交配的分裂泛素系统（mbSUS）中进行了蛋白质-蛋白质相互作用研究，并使用I-TASSER进行了伴随的蛋白质建模。尽管序列相似性非常有限且多肽插入可变，但所有AtMRS2蛋白都具有为CorA晶体结构确定的关键结构元件。mbSUS设置最终证明了任何给定的AtMRS2蛋白不仅与其自身的蛋白质-蛋白质相互作用，而且在所有AtMRS2蛋白之间都存在不同程度的高度允许的相互作用。AtMRS2-3似乎特别容易与其他同源物发生非选择性的强相互作用。缺失构建体表明，从AtMRS2-7的羧基末端可以删除六个氨基酸，从氨基末端可以删除27个（但不是41个），而不会损害同源或异源蛋白质相互作用。尽管有显著的多样性，植物MRS2蛋白显然保留了古老的CorA/MRS2核心结构和蛋白质-蛋白质相互作用的能力。植物镁稳态可能受到异源寡聚体通道形成的影响，其中不同的植物MRS2蛋白在同一膜中自然相遇或通过转基因方法相遇。
