ONE-SIDED PORES FORMED BY NYSTATIN IN LIPID BILAYER MEMBRANES

Abstract

The polyene antibiotic, nystatin, forms pores in eukaryotic cell membranes as well as in artificial membranes that contain sterol. In sterol-containing planar artificial bilayers, nystatin forms two types of pores. When added to only one side of the membrane, it forms cation-selective channels (the one-sided pores) yet when added simultaneously to both sides of the membrane, it forms anion-selective channels (the two-sided pores). The molecular model of Finkelstein, Holz, and Marty proposes that the one-sided pore consists of 8 - 10 nystatin monomers arranged circumferentially like the staves of a barrel with sterol molecules bound between the monomers. Two of these one-sided "barrels" joined end to end form the two-sided pore. I have tested three major predictions of this model. (1) The model assumes that the one molecular species, i.e., nystatin forms both the one- and two-sided pores. I have purified the commercial Squibb Nystatin by HPLC and shown that both pores are formed by only one of the four separated fractions. (2) The model predicts that the one-sided pore is 1/2 the thickness of the two-sided pore. I examined the activities of both pores on membranes made from a series of monoglycerides of varying acyl chain lengths. I have found that the one-sided pore forms only on the monoglyceride membranes of 18 carbon atom acyl chain length or less, while the two-sided pore forms on membranes of all thicknesses, indicating that the one-sided pore is shorter than the two-sided pore. (3) By comparing the permeability of urea and glycerol through the one- and two-sided pores, I have shown that the inner diameters of both pores are identical as predicted by the model.;In addition, I have characterized the cation-selective one-sided nystatin pore. It has a 5pS conductance in 2MKCl. My data indicate that the one-sided nystatin channels induced in artificial membranes are identical to those formed physiologically in cell membranes.;*Work completed in 1983, but degree will be granted in 1984.