Abstract
We describe phospholipid bilayer sensors for detection of activity of cholesterol dependent cytolysins (CDCs) comprising a class of structurally related proteins. We focus on vaginolysin (VLY) secreted by the bacteria Gardnerella vaginalis, which is a virulent factor in bacterial vaginosis. CDCs are strictly dependent on cholesterol. To measure the activity of VLY we developed tethered bilayers with controlled amount of cholesterol. Such bilayers are sensitive to VLY in a concentration dependent manner. Sensitivity of bilayers can be modulated by the cholesterol content. Membrane damage by VLY is easily detected at the subnanomolar concentration range utilizing the electrochemical impedance spectroscopy (EIS). An EIS data analysis algorithm allowing estimating density of protein pores is presented. Other pore-forming cholesterol dependent toxins such as intermedilysin affects phospholipid bilayer in a similar way as VLY. However, to achieve maximal performance of a phospholipid sensor the composition of tethered bilayers needs to be adjusted individually.