Non-Specific Cation Channels in Yeast Plasma Membranes

每一个微小的类似细胞的生物单元都由一个薄脂表面膜分隔，表面膜上掺杂着各种蛋白质分子，这些分子的共同任务是向细胞通报其环境，抵御恶劣环境，并维持营养物质的内运和废物的外运，使其足以正常发育。自由生活的“模型”细胞，如常见的面包师酵母，其膜直接暴露在环境中--以及研究人员--已经成为研究这种重要的膜过程的强大工具。这项关于酵母膜的新研究的主要目标是确定一种名为NSC1的蛋白质，它负责在类植物(P)和类动物(A)行为之间切换真菌膜，其中关键区别是主要由电驱动运输决定的低渗透性，而与化学驱动运输有关的高渗透性。正常情况下，外部盐(氯化钠)的显著升高会触发P_A转换，但在实验室中，最好的转换是通过耗尽细胞外钙来完成，并通过重新添加二价金属离子或多价氨基阳离子来逆转。后一种试剂正被用于对酵母中NSC1蛋白的存在或缺失进行功能筛选，这些酵母通过基因文库进行系统突变或转化。基因和蛋白质之间已建立的对应关系，加上公认的对整个酵母基因组的了解，应该会揭示NSC1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，又增强或抑制活性；c)用新的试剂作为生长促进剂或抗生素来靶向蛋白质。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。通过减少植物根膜发生这种转换的趋势，应用a、b应该立即有利于盐碱地的农业；应用c应该有助于抑制主要的植物病原体(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).