Reconstitution of Bacterial Targets in Model Membranes for a Biosensor-based Functional Analysis and Screening of Antibiotics

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A large number of antibiotics exert their activity by interacting with bacterial cell membranes or targets therein. The prototype lantibiotic nisin combines two killing mechanisms in one molecule, inhibition of cell wall biosynthesis and formation of specific membrane pores. For both it uses the cell wall precursor lipid II as a target and anchor molecule. We introduce a planar model membrane system to simulate the antibiotic activity of compounds and to interpret their mode of action. Two combined biosensors, quartz crystal microbalance (QCM) and cyclic voltammetry (CV) allow to follow the target binding of and membrane permeabilization by antibiotics in real time, either simultaneously or separately. The detection of kinetic binding constants (QCM) can validate the role of certain membrane targets, such as C55P, C55PP, lipid I and lipid II. Isothermal titration calorimetry measurements will supplement the binding data. CV studies of pore formation will be completed by atomic force microscopy. The investigations with nisin will be extended to a series of lantibiotics to delineate structure-activity relationships within this class of antibiotics. Furthermore, these techniques will be applied to other compounds from the consortium (especially lipopeptides, such as daptomycin, friulimicin or empedopeptin) to study for membrane targets and the mode of action. The biosensor based analysis of structurefunction correlations of dual action antibiotics will give directions for the design of innovative antiinfectives.