Abstract
Biological membranes play a vital role in cell functioning, providing structural integrity, controlling signal transduction, and controlling the transport of various chemical species. Owing to the complex nature of biomembranes, the self-assembly of lipids in aqueous media has been utilized to develop model systems mimicking the lipid bilayer structure, paving the way to elucidate the mechanisms underlying various biological processes, as well as to develop a number of biomedical and technical applications. The hydration properties of lipid bilayers are crucial for their activity in various cellular processes. Of particular interest is the local membrane dehydration, which occurs in membrane fusion events, including neurotransmission, fertilization, and viral entry. The lack of universal technique to evaluate the local hydration state of the membrane components hampers understanding of the molecular-level mechanisms of these processes. Here, we present a new approach to quantify the hydration state of lipid bilayers. It takes advantage of the change in the lateral diffusion of lipids that depends on the number of water molecules hydrating them. Using fluorescence recovery after photobleaching technique, we applied this approach to planar single and multicomponent supported lipid bilayers. The method enables the determination of the hydration level of a biomimetic membrane down to a few water molecules per lipid.
Highlights
Phospholipid membranes are indispensable architectural components of cells, subcellular compartments, and nanometer-sized biological objects such as exosomes or viruses [1]
Lateral diffusion of DMoPC in single component supported lipid bilayer (SLB) as well as in phaseseparated DMoPC/egg SM/cholesterol 1:1:1 SLB was investigated by fluorescence recovery after photobleaching (FRAP) experiments at different hydration conditions, starting from fully hydrated to membrane equilibrated to ~0% relative humidity (RH)
This observation is clearly reflected in the FRAP traces for fully hydrated and dehydrated (~30% RH) membranes, as shown in Figure 2a,c, for single component and phase-separated SLBs, respectively
Summary
Phospholipid membranes are indispensable architectural components of cells, subcellular compartments, and nanometer-sized biological objects such as exosomes or viruses [1]. Biological membranes carry out a variety of other important functions, including but not limited to, mediating and modulating the transport of ions and sugars, regulating the permeability of nonelectrolytes, and facilitating signal transduction and metabolic reactions [3,4] Lipids, due to their amphiphilic nature, spontaneously self-assemble in the aqueous environment. Bilayers in the form of black lipid membranes, vesicles (free-standing or tethered to supports), and planar supported bilayers (interacting directly with a solid substrate or tethered to the substrate) are commonly used as biomimetic membranes [5] Such model systems, on the one hand, preserve the essential characteristic of the lipid bilayer and, on the other hand, simplify the biological membrane system so that the roles of the individual membrane components, as well as their organization and dynamics, can be effectively explored. The use of biomimetic membranes, often integrated with functional proteins, has proven to be a powerful tool used in drug screening [6,7,8] and delivery systems [9,10], artificial cell design [11], nanoreactors [12,13], biosensors [14,15,16], and the most commercially developed water purification applications [17,18,19], to name just a few spectacular examples from the very long list reported in the literature
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