Viscoelastic changes measured in partially suspended single bilayer membranes

Abstract

For studies involving biomimetic phospholipid membrane systems, such as membrane-protein interactions, it is crucial that the supported membrane is biomimetic in its physical properties as well as in its composition. Two often overlooked aspects of biomimicry are the need for unrestrained lipid mobility, reflected in the viscoelastic properties of the membrane, and sufficient space between the membrane and the support for the insertion of transmembrane proteins. Here we show for a series of DMPC-based membranes that a partially suspended single bilayer membrane can be formed on functionalized gold surface without tethering. These membranes exhibit sufficient freedom of motion to represent the viscoelastic properties of a free lamellar bilayer membrane as demonstrated by determining the phase transition temperatures of these single bilayer membranes from the viscosity change upon chain melting using the dissipation signal of a quartz crystal microbalance (QCM-D). Atomic force microscopy imaging confirmed confluent, smooth membrane coverage of the QCM-D sensor that completely obscured the roughness of the sputtered gold surface. High-force AFM imaging was able to push membrane patches into the valleys of the gold morphology, confirming the inherently suspended nature of the MPA supported membrane. We show that the correlation between frequency and dissipation changes in the QCM-D sensograms is a sensitive indicator of the morphology of the membrane.

Membrane Core-Specific Antimicrobial Action of Cathelicidin LL-37 Peptide Switches Between Pore and Nanofibre Formation

“…All experiments were performed following an established protocol that involved flushing 1 ml of liposome solution through the measurement chamber at 100 μL/min and at 19 °C35. Peptides were injected into the QCM chamber following the formation of the single bilayer: 13–15 Hz frequency and 2.5–3.0 × 10 −6 dissipation change was confirmed2846. Control experiments on MPA coated gold confirmed the absence of peptide binding.…”

“…Hence, there are many uncertainties around the mechanism of LL-37 action and attention has shifted to developing more active variants of LL-37 using systematic mutation2627 while the study of the actual mechanism of action has been largely neglected. In this work, the mechanism of action of LL-37 is probed in vitro using a comprehensive biophysical approach centred on the combination of a biomimetic membrane platform28 with the quartz crystal microbalance fingerprinting method29.…”

Formation of Alkanethiol Supported Hybrid Membranes Revisited

“…Solid‐supported lipid membranes are frequently used to mimic phospholipid bio‐interfaces, with widespread applications in biophysics and biomedical research . Solid supported membranes can be prepared using a range of methods; what is common in these that, depending on the intrinsic properties of the substrates, lipid molecules can assemble either into a bilayer or a monolayer on the support (with the exception when they remain in a pre‐existing morphology as, e.g., vesicles or cubosomes) . The formation of phospholipid bilayers was achieved by various deposition methods on polar metal oxide surfaces such as titanium oxide, aluminum oxide, silicon oxide, indium tin oxide, as well as oxygen‐plasma treated graphene and even bare gold .…”

“…Therefore it is possible that the hydrophobic surfaces used for the formation of hybrid membranes do not trigger liposome rupture on their own, and the process depends on differences in environmental factors, such as the presence/absence of ions. Hence there is an impetus to revisit the formation of hybrid membranes following the protocols of the well established liposome deposition method …”

“…QCM‐D was used to monitor the real‐time deposition of liposomes on alkanethiol monolayers, and fluorescence microscopy was used to characterize the morphology of the lipid aggregates on the QCM‐D sensor. 1, 2‐dimyristoyl‐ sn ‐glycero‐3‐phosphocholine (DMPC) lipid was used in all experiments for easy comparison to prior works on bilayer deposition …”