Morphological changes of bacterial model membrane vesicles

Abstract

Unilamellar vesicles frequently serve as model membrane systems to study membrane‐peptide and membrane‐protein interactions. They are formed either from natural lipid extracts that contain complex lipid mixtures, or from synthetic one‐, two‐, or multi‐component lipid mixtures mimicking the lipid composition of biological membranes. Unilamellar vesicles can be prepared by extrusion of aqueous multilamellar phospholipid suspensions and they can have limited stability due to aggregation and fusion processes. We used cryo‐transmission electron microscopy (cryoTEM) to study the morphology of vesicles of phosphatidylethanolamines (PEs), phosphatidylglycerols (PGs), and cardiolipins (CLs) that represent the major lipid components of cytoplasmic membranes of Gram‐negative bacteria. Our results show that single‐component vesicles of PE and PG stored at RT are stable in shape and size for at least 1 wk. In contrast, two‐component vesicles of PE/PG and PE/CL transform into lamellar sheets already several hours after preparation, which is probably due to a compensation of different spontaneous curvatures of PG lipids compared to PE and CL. With this investigation we intend to alert researchers working with model membranes to scrutinize the shape and stability of vesicles before using them in protein‐vesicle interaction studies. Practical applications: Liposomes represent widely‐used model membrane systems that are applied to mimic natural membranes. Usually, these liposomes are composed of one or two lipid components representing the major lipid constituents of the respective natural membrane. Their long‐term shape, aggregation, and fusion stability is an important prerequisite for the study of peptide‐liposome and protein‐liposome interactions, where the binding of peptides or proteins can have serious impacts on the liposomal shape and size. Furthermore, shape and size stability is of outstanding importance for the application of liposomes as drug‐delivery system. We showed that single‐component liposomes composed of the major lipid components of cytoplasmic membranes of Gram‐negative bacteria (PE and PG) are stable in shape and size for at least 1 wk, whereas the corresponding two‐component liposomes become unstable within hours and transform into discs and sheets. This knowledge will be indispensable for future studies on interactions of liposomes with peptides and proteins. Cryo‐transmission electron microscopy is the method of choice to study the size, morphology, and shape stability of liposomes being composed of the phospholipids PE, PG, and CL that represent the major lipid components of cytoplasmic membranes of Gram‐negative bacteria.

Interaction of Giant Unilamellar Vesicles with the Surface Nanostructures on Dragonfly Wings

“…24,25 Their large size, simplicity, and adaptable composition make them suitable for application as an adjustable model of a bacterial cell membrane, allowing an analysis of each of the individual membrane components in isolation. 26 In this study, GUVs were utilized as a simplified model of the cell membrane in order to investigate the interactions taking place between the membrane and the mechanobactericidal nanostructured surface of Austrothemis nigrescens and Trithemis annulata dragonfly wings. By constructing the GUV membrane using 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), with known biophysical properties, we were able to establish the range of stretching forces that can be imparted on the membrane by the nanofeatures that present on the dragonfly wings and thus infer the range of the tensions that are imposed on the cell membrane models by the dragonfly wings.…”

“…Giant unilamellar vesicles (GUVs) are simple, synthetically produced spheres, consisting of a thin unilamellar membrane that encloses a given solution. − GUVs can range from 1 to 150 μm in diameter. − Unilamellar vesicles have been used for studying cellular protein activity, drug delivery systems, and the biophysical properties of membranes. − GUVs can be well defined, with highly controllable features such as membrane composition, rigidity, internal contents, and turgor pressure. , Their large size, simplicity, and adaptable composition make them suitable for application as an adjustable model of a bacterial cell membrane, allowing an analysis of each of the individual membrane components in isolation …”

(Cryo)Transmission Electron Microscopy of Phospholipid Model Membranes Interacting with Amphiphilic and Polyphilic Molecules

“…The aggregates might be composed of lipids, surfactants, liquid crystals, peptides, proteins, polymers, drugs, and mixtures which form aggregate structures such as vesicles, fibers, discs, or micelles. Even mixtures of these aggregates can easily be distinguished [ 20 , 21 , 22 , 23 , 24 , 25 , 26 ].…”

Study of the solubilisation process of bacterial model membranes induced by DDAO

“…The aim of this study was to determine how different (Lopes et al, 2010). The fatty acids found in the E. coli membrane phospholipids are predominantly 16-18 carbon long, with a substantial portion of them being unsaturated (Meister et al, 2014). For this reason, we chose to use a mixture of palmitoyloleoylphosphatidylethanolamine (POPE) and palmitoyloleoylphosphatidylglycerol (POPG) as our model system, in a molar ratio of POPE/POPG = 0.6/0.4 mol/mol.…”