Weak Acid Permeation in Synthetic Lipid Vesicles and Across the Yeast Plasma Membrane

Matteo Gabba,Jacopo Frallicciardi,Joury Van ’T Klooster,Ryan Henderson,Łukasz Syga,Robert Mans,Antonius J.A Van Maris,Bert Poolman

doi:10.1016/j.bpj.2019.11.3384

Matteo Gabba, Jacopo Frallicciardi + Show 6 more

Open Access

https://doi.org/10.1016/j.bpj.2019.11.3384

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Abstract

We present a fluorescence-based approach for determination of the permeability of small molecules across the membranes of lipid vesicles and living cells. With properly designed experiments, the method allows us to assess the membrane physical properties both in vitro and in vivo. We find that the permeability of weak acids increases in the order of benzoic > acetic > formic > lactic, both in synthetic lipid vesicles and the plasma membrane of Saccharomyces cerevisiae, but the permeability is much lower in yeast (one to two orders of magnitude). We observe a relation between the molecule permeability and the saturation of the lipid acyl chain (i.e., lipid packing) in the synthetic lipid vesicles. By analyzing wild-type yeast and a manifold knockout strain lacking all putative lactic acid transporters, we conclude that the yeast plasma membrane is impermeable to lactic acid on timescales up to ∼2.5 h.

Highlights

Many cellular processes and the robustness of cells to environmental conditions lean on the biophysical properties of the plasma membrane, which is the lipid bilayer separating the intracellular environment from the external world
These processes include 1) the activity of membrane proteins, which depends on the lipid composition of the membrane; 2) the encounter rate of two molecular partners embedded in the membrane, which depends on their lateral diffusion; and 3) cellular metabolism, which is affected by the passive diffusion across the plasma membrane of some chemical species
It is generally believed that this is the major mechanism behind the use of weak acids as food preservatives [7]; the other mechanism relates to toxicity effects of the corresponding anions on cellular metabolism [8]

Summary

Introduction

Many cellular processes and the robustness of cells to environmental conditions (pH, temperature, osmolality) lean on the biophysical properties of the plasma membrane, which is the lipid bilayer separating the intracellular environment from the external world. These processes include 1) the activity of membrane proteins (transporters, receptors, etc.), which depends on the lipid composition of the membrane; 2) the encounter rate of two molecular partners embedded in the membrane, which depends on their lateral diffusion; and 3) cellular metabolism, which is affected by the passive diffusion across the plasma membrane of some chemical species (ethanol, CO2, water, weak acids, etc.). This illustrates the importance of developing an easy method to monitor the diffusion of weak acids across the membranes of living cells

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