Fliegel Larry
Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Mol Cell Biochem. 2005 Jan;268(1-2):83-92. doi: 10.1007/s11010-005-3696-6.
The Na+/H+ exchanger is a ubiquitous protein that transports Na+ and H+ in opposite directions across cell membranes. In fission yeast, the Na+/H+ exchanger sod2 plays a major role in the removal of excess detrimental intracellular sodium. The effect of mutagenesis of conserved polar amino acids of sod2 was examined by expressing 10 different mutant forms of sod2 in sod2 deficient S. pombe and characterizing salt tolerance. Asp145, 266, 267, and Glu173 were critical for proper function of sod2. Asp241 had an intermediate effect on sod2 function while mutation of Asp178 did not impair sod2 function. Simultaneous mutation of the Asp266, 267 pair impaired sod2 function. Mutation of each individual residue demonstrated that both were critical for sod2 function. Conservative mutations (Asp to Glu) of Asp266 and 267 failed to restore sod2 function. The results suggest that acidic residues associated with transmembrane segments are important in function, possibly being important in binding and coordinating cations.
钠氢交换体是一种普遍存在的蛋白质，它能使钠离子和氢离子以相反方向跨细胞膜运输。在裂殖酵母中，钠氢交换体sod2在清除细胞内多余的有害钠离子方面发挥着主要作用。通过在缺乏sod2的粟酒裂殖酵母中表达10种不同的sod2突变形式并对耐盐性进行表征，研究了sod2保守极性氨基酸诱变的影响。Asp145、266、267和Glu173对sod2的正常功能至关重要。Asp241对sod2功能有中等影响，而Asp178突变并不损害sod2功能。Asp266、267这一对氨基酸同时突变会损害sod2功能。对每个单独残基的突变表明两者对sod2功能都至关重要。Asp266和267的保守突变（Asp突变为Glu）未能恢复sod2功能。结果表明，与跨膜区段相关的酸性残基在功能上很重要，可能在结合和协调阳离子方面发挥重要作用。
