Charges inside a bacterial channel shift unpredictably with salt and voltage.

Proteins in cell membranes act as tiny gates that open, close, and sort molecules. These jobs depend on whether specific protein parts hold onto or release protons, which are tiny charged particles. Scientists tested the bacterial channel OmpF to see how salt levels, electrical voltage, and protein shapes change these proton charges. They ran computer simulations that let acid groups gain or lose protons under different conditions. They discovered that raising salt concentration changes proton-holding ability, known as pKapKaA number that tells you how likely a chemical group is to lose a proton; lower pKa means it loses protons more easily., in complex ways rather than following a simple pattern. Applying an electric voltage creates small, opposite charge shifts on opposite sides of the protein. Finally, these charge changes happen with very little backbone movement, though some side branches rotate or shift significantly.

Why it matters

Many bacteria rely on porin channels like OmpF to let nutrients in and keep toxins out. This study shows that the channel's internal charges—which control its opening and selectivity—are surprisingly sensitive to salt concentration and voltage in ways that don't follow simple rules. These findings could help design better antibiotics that exploit or block these channels, and improve our understanding of how cells regulate their membranes under changing conditions.

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