Characterization of planar biomimetic lipid films composed of phosphatidylethanolamines and phosphatidylglycerols from Escherichia coli

Abstract

We have characterized planar lipid films composed of phosphatidylethanolamines (PE) and phosphatidylglycerols (PG) from E. coli bacteria. The nature of the interactions and miscibility of PE and PG components within mixed lipid films was evaluated based on surface pressure measurements and Brewster angle microscopy imaging at the air-water interface. We have found that PE and PG components show tendency to form separated domains at surface pressures relevant for biological membranes. Further, we have directly compared mechanisms of formation of supported lipid bilayers either on mica or Au(111) by spreading of small unilamellar vesicles. The bilayer formation was monitored by in situ atomic force microscopy imaging. The pathways of the vesicles spreading on each substrate are substantially different and the buildup of the bilayer on Au(111) occurs through complex multistep mechanism. The morphology and nanomechanical properties of the resulting PE/PG bilayers were thoroughly compared. We have found that the interactions between lipids and supporting substrate significantly affect molecular organization within the films since the bilayer on Au(111) is uniform in terms of the topography, while the same lipid composition on mica results in formation of distinct gel and liquid disordered domains. Different molecular organization affects also nanomechanical properties of lipid films. The latter were expressed in terms of Young's moduli and bending stiffness.

Supported Lipid Bilayers of Escherichia coli Extracted Lipids and Their Calcium Dependence

“…The result is consistent with previous studies, which showed at least ∼2 mM of Ca 2+ is necessary for the formation of PLE-SLB on SiO 2 /Si, mica, TiO 2 , indium tin oxide and gold (Dodd et al, 2008;Merz et al, 2008;Lopes et al, 2010;Unsay et al, 2013;Lind et al, 2015;Hsia et al, 2016;Konarzewska et al, 2017;Márquez and Vélez, 2017). In the previous studies of the bacterial mimic lipid bilayer, however, averaged response from the sample was mainly obtained using QCM and fluorescence microscopy (Dodd et al, 2008;Merz et al, 2008;Lopes et al, 2010;Unsay et al, 2013;Lind et al, 2015;Phan and Shin, 2015;Hsia et al, 2016;Konarzewska et al, 2017;Márquez and Vélez, 2017). The results in this study showed the heterogeneity of SLB especially at the threshold [Ca 2+ ] around 2.5 mM.…”

“…As a bacterial model cell system, reconstituted Escherichia coli (E. coli) cell membrane has been studied (Dodd et al, 2008;Merz et al, 2008;Lopes et al, 2010;Unsay et al, 2013;Lind et al, 2015;Phan and Shin, 2015;Hsia et al, 2016;Konarzewska et al, 2017;Márquez and Vélez, 2017). Understanding the bacterial membrane system helps in revealing the mechanism of molecular recognition and material transportation during bacterial infection for medical technology.…”

“…There are several previous studies on the formation of SLBs containing E. coli lipids such as polar lipid extract (PLE) or total lipid extract (TLE) (Dodd et al, 2008;Merz et al, 2008;Lopes et al, 2010;Unsay et al, 2013;Lind et al, 2015;Hsia et al, 2016;Konarzewska et al, 2017;Márquez and Vélez, 2017). Solid substrates, which are generally used for SLB formation, e.g., glass, oxidized layer on a Si wafer, and mica, are negatively charged.…”

Physicochemical Characterization of Sparsely Tethered Bilayer Lipid Membranes: Structure of Submembrane Water and Nanomechanical Properties

“…For example, the Young's moduli found for lipid bilayers immobilized on mica vary from 18 MPa to 40 MPa depending on physical state of the membrane. [27,28] Similar range of values was also reported for floating bilayer lipid membranes (fBLM). [29] The latter possess water cushion between lipid membrane and the electrode modified with hydrophilic monolayer (e. g. thioglucose).…”

Properties of Omp2a-Based Supported Lipid Bilayers: Comparison with Polymeric Bioinspired Membranes

“…51,52 However, the modulus of elasticity of ∼18 MPa was recently reported for L α phase of the mica-supported bilayer composed of lipids extracted from E. coli . 53 Moreover, the modulus of polymeric FsNMs was reported to increase from ∼25 to ∼35 MPa with the thickness (i.e., from 10–20 to ∼80 nm). 54…”