Location and role of sterol at nystatin-binding sites.

Lampen, J. O. (Rutgers, The State University, New Brunswick, N.J.), Peter M. Arnow, Zofia Borowska, and Allen I. Laskin. Location and role of sterol at nystatin-binding sites. J. Bacteriol. 84:1152-1160. 1962.-The polyene antifungal antibiotics nystatin and N-acetylcandidin were bound rapidly at 0 C by isolated cell walls and derived polysaccharides or by protoplast membranes from Saccharomyces cerevisiae strain LK2G12. These binding sites were relatively inaccessible or unreactive in the intact cell, since polyene uptake by protoplasts, log-phase cells, or stationary-phase cells was slow, especially at 0 C. Binding by the membrane appears to be the critical event in cell damage; thus, uptake of nystatin by the cell wall may actually be protective. Binding by all cell forms showed little reversibility. Bound radioactive nystatin or N-acetyl (1-C(14)) candidin was not displaced during incubation of log-phase yeast cells with a large excess of unlabeled polyene. Saturation of the polyenic moiety of nystatin to form the perhydro compound eliminated almost completely the affinity of the molecule for the yeast cell. Essentially all of the polyene bound by protoplasts was present on the membrane. It was removed by treatment of the protoplasts with the sterol-complexing agent digitonin. A variety of evidence is offered that the binding site on the membrane contains a sterol. (The membrane sterol was mostly unesterified ergosterol.) This hypothesis is consistent with the ability of certain exogenous sterols to complex with polyenes and prevent their binding and growth-inhibiting action for fungi. The bound sterol of the wall structure may also participate in polyene binding, although a possible function of the wall polysaccharides cannot be excluded. The specific binding structure(s) appears to be absent from bacteria, since nystatin was not taken up even by heated or benzene-treated bacteria or by bacterial protoplasts. It should be noted that bacteria, which are insensitive to the polyene antibiotics, generally contain only traces of sterol, if any. Considerable quantities of sterol are present in fungi, algae, certain protozoa, and animal cells, all of which are sensitive in some degree.