Regulation of membrane protein activity by cyclopropane fatty acids in Escherichia coli lipid environment

Membrane proteins are crucial in cellular processes like signal and energy transduction and are influenced by the properties of the surrounding lipid bilayer. Fatty acids, key components of phospholipids, adjust membrane properties in response to environmental changes; however, their direct effect on membrane protein activity is poorly understood. Cyclopropane fatty acids (CFAs) are produced by a cyclopropane fatty acid synthase (Cfa) by adding a methylene group to unsaturated fatty acids. CFAs are abundant in the membranes of Escherichia coli, particularly during the stationary phase or stress conditions, and are believed to contribute to modulating membrane rigidity and permeability, yet their functional role in membrane protein regulation remains unclear. Here, we examined the effect of CFAs on the activity of NhaA, a Na⁺/H⁺ antiporter in E. coli, using Δcfa mutants deficient in CFA synthesis. NhaA activity exhibits a strong negative correlation with the ratio of cyclopropane to saturated fatty acids. Molecular dynamics simulations showed that CFA reduces NhaA-phospholipid interactions, restricting the conformational change needed for activation. These results suggest that membrane protein activity can be regulated by fatty acid composition, with CFAs playing a significant role.