Lipid rafts can form in the inner and outer membranes of Borrelia burgdorferi and have different properties and associated proteins

Lipid rafts are microdomains present in the membrane of eukaryotic organisms and bacterial pathogens. They are characterized by having tightly packed lipids and a subset of specific proteins. Lipid rafts are associated with a variety of important biological processes including signaling and lateral sorting of proteins. To determine whether lipid rafts exist in the inner membrane of Borrelia burgdorferi, we separated the inner and outer membranes and analyzed the lipid constituents present in each membrane fraction. We found that both the inner and outer membranes have cholesterol and cholesterol glycolipids. Fluorescence anisotropy and FRET showed that lipids from both membranes can form rafts but have different abilities to do so. The analysis of the biochemically defined proteome of lipid rafts from the inner membrane revealed a diverse set of proteins, different from those associated with the outer membrane, with functions in protein trafficking, chemotaxis and signaling.