Non-Specific Cation Channels in Yeast Plasma Membranes

Yale University, New Haven CT

Investigators

Abstract

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).