Exploring the Existence of Lipid Rafts in Bacteria

Abstract

1. Summary An interesting concept in the organization of cellular membranes is the proposed existence of lipid rafts. Membranes of eukaryotic cells organize signal transduction proteins into membrane rafts or lipid rafts, that are enriched in particular lipids like cholesterol and are important for the correct functionality of diverse cellular processes. The assembly of lipid rafts in eukaryotes has been considered a fundamental step during the evolution of cellular complexity, suggesting that bacteria and archaea were too simple organisms to require such a sophisticated organization of their cellular membranes. However, it was recently discovered that bacteria organize many signal transduction, protein secretion and transport processes in functional membrane microdomains, which are equivalent to the lipid rafts of eukaryotic cells. This review contains the most significant advances during the last four years to understand the structural and biological role of lipid rafts in bacteria. Furthermore, this review shows a detailed description of a number of molecular and genetic approaches related to the discovery of bacterial lipid rafts as well as an overview of the group of tentative lipid-protein and protein-protein interactions that give consistency to these sophisticated signaling platforms. Additional data is presented in this review suggesting that lipid rafts are widely distributed in bacteria. Therefore, we discuss the available techniques and optimized protocols for the purification and analysis of rafts-associated proteins in various bacterial species to purposively the study of bacterial lipid rafts to other laboratories that could be interested in the topic. Overall, the discovery of lipid rafts in bacteria reveals a new level of sophistication in signal transduction and membrane organization that was unexpected in bacteria and shows that bacteria are more complex organisms than previously appreciated.

Hopanoids as functional analogues of cholesterol in bacterial membranes

“…It will be important to understand how lipid order influences the dynamics of OM proteins, such as their structure, insertion into the membrane, lateral diffusion, and dimerization. Furthermore, it remains unknown if the OM is capable of lateral compartmentalization as has been proposed to occur in other bacterial membranes (57). Do hopanoids promote such membrane organization?…”

Daptomycin inhibits cell envelope synthesis by interfering with fluid membrane microdomains

“…Transitions between the fluid lipid-daptomycin clusters (rigidified through tight clustering of fluid, short-chain lipids) and the more rigid (thicker) bulk of the cell membrane likely constitute such weak spots through which proton leakage can occur and might explain the gradual depolarization of the membrane. It should be mentioned that phase-boundary defects as a cause for membrane permeabilization have been studied only in vitro, and it remains to be seen how phase separation affects the barrier function of bacterial membranes that naturally contain lipid domains of different fluidity (38,77,78). Nonetheless, daptomycin-induced changes in bilayer organization lead to a slow increase in the passive permeability of the membrane, which may be why membrane pore formation has been considered the main function of daptomycin in former studies (16,17,31).…”

Recent progress on lipid lateral heterogeneity in plasma membranes: From rafts to submicrometric domains

“…However, it has been recently shown that bacteria organize many signal transduction, protein secretion and transport processes in functional membrane microdomains, which seem equivalent to eukaryotic lipid rafts (reviewed in [161]). The formation of these functional membrane microdomains seems to require flotillin-like proteins.…”