Multiscale Simulations of Membrane Recognition by Lipid Kinases

Abstract

of pneumonia, daptomycin is curiously inhibited by lung surfactant and is rendered ineffective against Gram-positive Streptococcus pneumoniae, the primary cause of this illness. The reason for this is currently not understood. We developed lipid model systems to mimic S. pneumoniae membranes, tissue cell membranes, and both synthetic and natural (BLES) lung surfactant. Using the Langmuir-Blodgett trough, constant-area insertion assays were performed. It was discovered that daptomycin inserts into lung surfactant to a greater extent than it does with bacterial membrane at physiologicallyrelevant calcium concentrations. Fluorescence spectroscopy data provided us with results corroborating the findings from the insertion assays. Meanwhile, compression isotherms provided data on monolayer compressibility. We found that daptomycin and calcium can improve surfactant activity and performance, suggesting the formation of multilayers at lower pressures. Atomic force microscopy and Kelvin probe force microscopy imaging provided visual evidence of multilayer formation induced by the presence of daptomycin and calcium, confirming this mechanism of inhibition. Based on these results, we propose a novel model of daptomycin sequestration by lung surfactant (see figure ), where (1) daptomycin inserts into surfactant, (2) lowers its compressibility, (3) induces multilayer formation, and (4) reinforces its sequestration, rendering it unable to exert its bactericidal activity against S. pneumoniae.