Binding of yeast killer toxin to a cell wall receptor on sensitive Saccharomyces cerevisiae

Abstract

3S-labeled killer toxin protein bound to cells of sensitive Saccharomyces cerevisiae S14a. Strains that were resistant to toxin through mutation in the nuclear genes krel or kre2 bound toxin only weakly. Non-radioactive toxin competed effectively with 35S-labeled toxin for binding to S14a, but did not compete significantly in the binding to mutant krel-1. This implied that binding to krel-1 was nonspecific. A Scatchard analysis of the specific binding to S14a gave a linear plot, with an association constant of 2.9 x 106 M-' and a receptor number of 1.1 x 107 per cell. Killer toxin receptors were solubilized from the cell wall by zymolyase digestion. Soluble, non-dialyzable cell wall digest from S14a competed with sensitive yeast cells for 3S-labeled toxin binding and reduced toxin-dependent killing of a sensitive strain. Wall digest from krel-1 competed only weakly for toxin binding with sensitive cells and caused little reduction of toxin-dependent killing. Although the abundant (1.1 x 107 per cell) wall receptor appeared necessary for toxin action, as few as 2.8 x 104 toxin molecules were necessary to kill a sensitive cell of S14a. The kinetics of killing of S14a suggested that some component was saturated with toxin at a concentration 50-fold lower than that needed to saturate the wall receptor.

Differential growth inhibition as a tool to increase the discriminating power of killer toxin sensitivity in fingerprinting of yeasts

“…In agreement with the current literature [12,13] which seems to indicate a mechanism of possible toxin binding until saturation of free receptors, the rationale of this behavior could be found in both the di¡erent concentration of the toxin and the di¡erent number of free receptors available on sensitive cell walls for interaction. As a matter of fact, several authors suggested that the type [22,23] and the number [13] of free active sites di¡er among di¡erent sensitive strains.…”

“…Di¡erent mycocins seem to exhibit di¡erent mechanisms of action involving either pore formation (with subsequent loss of potassium ions, ATP and disruption of the cell electrochemical potential across the membrane) or the arrest in the G1 phase of the cell cycle [4,5]. In addition, previously observed di¡erential doser esponses to the e¡ect of a same crude toxin [12,13] have been interpreted as a result of both the number of molecules of mycocin and of the variable number of spe-ci¢c receptors available on sensitive cell walls. Along these lines, the possible`quanti¢cation' of the killing activity (di¡erential growth inhibition) of selected toxins against a pool of sensitive strains may provide an additional and supplementary tool in increasing their discriminating power.…”

Fungal Viral Mutualism Moderated by Ploidy

“…We set out to examine a mechanistic hypothesis to explain this ploidy-specific difference in sensitivity. Haploids differ from diploids in a number of ways, they produce pheromones and pheromone receptors, and they are smaller (Bussey et al 1979). Smaller haploid cells typically contain proportionally smaller amounts of cellular components (Weiss et al 1975), and the toxin receptor, β-1,6 glucan, is a major component of the cell wall making up ∼12% of cell wall polysaccharide (Lesage and Bussey 2006), suggesting that haploids have fewer toxin receptors.…”

Cell‐division inhibitor produced by a killer strain of cellular slime mold Polysphondylium pallidum

“…Killer toxins of yeasts are known to bind specifically to a receptor on the cell surface (3,7). We found that inhibition of cell division by the celldivision inhibitor was reversed by trypsin-treatment of the cells, suggesting that this inhibitor also binds to a receptor on the cell surface.…”

“…Cells treated with CM do not proliferate even after transfer to fresh BSS culture. This fact suggests that the cell-division inhibitor in CM binds to a cell surface receptor like killer toxins of yeasts (3,7). If this is the case, the inhibition of cell-division by treatment with CM might be reversed by treating the cells with trypsin.…”