MacDiarmid C W, Gardner R C
School of Biological Sciences, University of Auckland, New Zealand.
J Biol Chem. 1998 Jan 16;273(3):1727-32. doi: 10.1074/jbc.273.3.1727.
Ionic aluminum (Al3+) is toxic to plants, microbes, fish, and animals, but the mechanism of its toxicity is unknown. We describe the isolation of two yeast genes (ALR1 and ALR2) which confer increased tolerance to Al3+ and Ga3+ ions when overexpressed while increasing strain sensitivity to Zn2+, Mn2+, Ni2+, Cu2+, Ca2+, and La3+ ions. The Alr proteins are homologous to the Salmonella typhimurium CorA protein, a bacterial Mg2+ and Co2+ transport system located in the periplasmic membrane. Yeast strains lacking ALR gene activity required additional Mg2+ for growth, and expression of either ALR1 or ALR2 corrected the Mg(2+)-requiring phenotype. The results suggest that the ALR genes encode the yeast uptake system for Mg2+ and other divalent cations. This hypothesis was supported by evidence that 57Co2+ accumulation was elevated in ALR-overexpressing strains and reduced in strains lacking ALR expression. ALR overexpression also overcame the inhibition of Co2+ uptake by Al3+ ions. The results indicate that aluminum toxicity to yeast occurs as a consequence of reduced Mg2+ influx via the Alr proteins. The molecular identification of the yeast Mg2+ transport system should lead to a better understanding of the regulation of Mg2+ homeostasis in eukaryote cells.
离子态铝（Al3+）对植物、微生物、鱼类和动物具有毒性，但其毒性机制尚不清楚。我们描述了两个酵母基因（ALR1和ALR2）的分离情况，当这两个基因过表达时，能赋予酵母对Al3+和Ga3+离子更高的耐受性，同时增加菌株对Zn2+、Mn2+、Ni2+、Cu2+、Ca2+和La3+离子的敏感性。Alr蛋白与鼠伤寒沙门氏菌的CorA蛋白同源，CorA蛋白是一种位于周质膜的细菌Mg2+和Co2+转运系统。缺乏ALR基因活性的酵母菌株生长需要额外的Mg2+，而ALR1或ALR2的表达可纠正这种对Mg2+的需求表型。结果表明，ALR基因编码酵母对Mg2+和其他二价阳离子的摄取系统。这一假设得到了以下证据的支持：在ALR过表达菌株中57Co2+积累增加，而在缺乏ALR表达的菌株中则减少。ALR过表达还克服了Al3+离子对Co2+摄取的抑制作用。结果表明，铝对酵母的毒性是由于通过Alr蛋白的Mg2+内流减少所致。酵母Mg2+转运系统的分子鉴定应有助于更好地理解真核细胞中Mg2+稳态的调节。
