Phospholemman (PLM), a 72-amino acid membrane protein with a single transmembrane domain, forms taurine-selective ion channels in lipid bilayers. Because taurine forms zwitterions, a taurine-selective channel might have binding sites for both anions and cations. Here we show that PLM channels indeed allow fluxes of both cations and anions, making instantaneous and voltage-dependent transitions among conformations with drastically different ion selectivity characteristics. This surprising and novel ion channel behavior offers a molecular explanation for selective taurine flux across cell membranes and may explain why molecules in the phospholemman family can induce cation- or anion-selective conductances when expressed in Xenopus oocytes.
Kowdley, G. C., Ackerman, S. J., Chen, Z., Szabo, G., Jones, L. R., & Moorman, J. R. (1997). Anion, cation, and zwitterion selectivity of phospholemman channel molecules. Biophysical Journal, 72(1), 141–145. https://doi.org/10.1016/S0006-3495(97)78653-3