Non-Specific Cation Channels in Yeast Plasma Membranes

每一个微观的“细胞”样的生命物质单位由一个薄的脂质表面膜界定，上面有各种蛋白质分子，这些蛋白质分子共同负责向细胞通报其环境，抵御恶劣的环境，并维持营养物质的向内运输和废物的向外运输，足以正常发育。 自由生活的“模型”细胞，如普通的面包酵母，其膜直接暴露于环境和发酵器，已经成为研究这种重要膜过程的有力工具。 这项关于酵母膜的新研究的主要目的是鉴定一种名为NSC 1的蛋白质，该蛋白质负责在植物样（P）和动物样（A）行为之间切换真菌膜，其中关键的区别是主要针对电驱动运输的低渗透性，而高渗透性则主要针对化学驱动运输。 正常情况下，外源性盐（NaCl）的升高会触发P_A转换，但在实验室中，这种转换最好通过消耗细胞外钙来实现，而通过重新加入二价金属离子或多价氨基阳离子来逆转。 后一种试剂用于在系统诱变或用基因文库转化的酵母中进行NSC 1蛋白存在或不存在的功能性筛选。 基因和蛋白质之间建立的对应关系，加上整个酵母基因组的公认知识，应该揭示NSC 1蛋白本身及其编码基因。 反过来，该基因将促进三个重要的实际应用：a）鉴定植物中相应的蛋白质; B）操纵蛋白质结构，既探索转换的分子机制，又增强或延缓活性; c）用设计为生长促进剂或抗生素的新试剂靶向蛋白质。 植物、真菌和细菌都是天然的P态生物，盐引发的P-A转换是盐碱地作物生产力低下的部分原因。 通过降低植物根膜发生这种转换的趋势，施用a、B应立即有益于盐碱地农业;施用c应有助于抑制主要植物病原体（主要是真菌）。

Each microscopic "cell"-like unit of living matter is delimited by a thin-lipid surface membrane, spiked with various protein molecules which are collectively tasked to inform the cell about its environment, to defend against hostile environments, and to sustain inward transport of nutrients and outward transport of waste products adequate for normal development. Free-living "model" cells, such as the common bakers' yeast, with membranes directly exposed to the environment-and to the investigator-have become a powerful tool for investigating such vital membrane processes. The primary objective of this new research on yeast membranes is to identify a protein, designated NSC1, which is responsible for switching fungal membranes between plant-like (P) and animal-like (A) behavior, where the critical difference is low permeability keyed mainly to electrically driven transport, versus high permeability keyed to chemically driven transport. Normally, gross elevation of external salt (NaCl) triggers P_A switching, but in the laboratory, switching is best accomplished by depleting extracellular calcium, and reversed by re-adding divalent metal ions or polyvalent amino cations. The latter reagents are being used in functional screens for the presence or absence of NSC1 protein, in yeast systematically mutagenized or transformed with gene libraries. The established correspondence between genes and proteins, plus accepted knowledge of the entire yeast genome, should reveal the NSC1 protein itself and its encoding gene. That gene, in turn, will facilitate three important practical applications: a) identification of corresponding proteins in plants; b) manipulation of protein structure, both to explore the molecular mechanism of switching and to enhance or retard activity; and c) targeting the protein with new reagents designed as either growth enhancers or antibiotics. Plants, fungi, and bacteria are all natural P-state organisms, and salt-triggered P-A switching is partly responsible for poor crop productivity in saline soils. By reducing the tendency of plant root membranes to undergo such switching, applications a,b should immediately benefit agriculture in saline soils; and application c should assist suppression of major plant pathogens (mostly fungi).