Shao Li, Abdel-Motaal Heba, Chen Jin, Chen Huiwen, Xu Tong, Meng Lin, Zhang Zhenglai, Meng Fankui, Jiang Juquan
Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, Harbin, China.
Front Microbiol. 2018 Apr 25;9:807. doi: 10.3389/fmicb.2018.00807. eCollection 2018.
Arginine-aspartate-aspartate (RDD) family, representing a category of transmembrane proteins containing one highly conserved arginine and two highly conserved aspartates, has been functionally uncharacterized as yet. Here we present the characterization of a member of this family designated RDD from the moderate halophile NEAU-ST10-40 and report for the first time that RDD should function as a novel Na(Li, K)/H antiporter. It's more interesting whether the highly conserved arginine/aspartate residues among the whole family or between RDD and its selected homologs are related to the protein function. Therefore, we analyzed their roles in the cation-transporting activity through site-directed mutagenesis and found that D154, R124, R129, and D158 are indispensable for Na(Li, K)/H antiport activity whereas neither R35 nor D42 is involved in Na(Li, K)/H antiport activity. As a dual representative of Na(Li, K)/H antiporters and RDD family proteins, the characterization of RDD and the analysis of its important residues will positively contribute to the knowledge of the cation-transporting mechanisms of this novel antiporter and the roles of highly conserved arginine/aspartate residues in the functions of RDD family proteins.
精氨酸 - 天冬氨酸 - 天冬氨酸（RDD）家族是一类跨膜蛋白，含有一个高度保守的精氨酸和两个高度保守的天冬氨酸，但其功能至今尚未明确。在此，我们对来自中度嗜盐菌NEAU - ST10 - 40的该家族成员RDD进行了表征，并首次报道RDD应作为一种新型的Na(Li, K)/H反向转运蛋白发挥作用。整个家族或RDD与其选定的同源物之间高度保守的精氨酸/天冬氨酸残基是否与蛋白质功能相关，这一点更具趣味性。因此，我们通过定点诱变分析了它们在阳离子转运活性中的作用，发现D154、R124、R129和D158对于Na(Li, K)/H反向转运活性不可或缺，而R35和D42均不参与Na(Li, K)/H反向转运活性。作为Na(Li, K)/H反向转运蛋白和RDD家族蛋白的双重代表，RDD的表征及其重要残基的分析将对了解这种新型反向转运蛋白的阳离子转运机制以及高度保守的精氨酸/天冬氨酸残基在RDD家族蛋白功能中的作用做出积极贡献。
