Figure 1.

(a) Binding of M²⁺ (M = Ca, Mg) with cardiolipin (CL), the major lipid component in S. aureus, converts the originally zero-intrinsic-curvature (C₀~ 0) lipid into M²⁺-CL complexes with negative intrinsic curvature (C₀ < 0). (b–d) Dye leakage assays using large unilamellar vesicles (LUVs) composed of 100% CL as a first-order model for S. aureus membranes. (b) Mg²⁺ at ≥7.2 mM caused significant carboxyl fluorescein (CF) leakage. (c,d) Ca²⁺, though (c) unable to cause detectable CF leakage, caused (d) appreciable quenching in the fluorescence intensity of intravesicular lucigenin. Controls are samples assayed similarly but without M²⁺ additions.