Tubulation of Supported Lipid Bilayer Membranes Induced by Photosensitized Lipid Oxidation

Atherosclerotic Oxidized Lipids Affect Formation and Biophysical Properties of Supported Lipid Bilayers and Simulated Membranes

Oxidized lipids arising from oxidative stress are associated with many serious health conditions, including cardiovascular diseases. For example, KDdiA-PC and KOdiA-PC are two oxidized phosphatidylcholines (oxPC) directly linked to atherosclerosis, which precipitate heart failure, stroke, aneurysms, and chronic kidney disease. These oxPCs are well-characterized in small particles such as low-density lipoprotein, but how their presence affects the biophysical properties of larger bilayer membranes is unclear. It is also unclear how membrane mediators, such as cholesterol, affect lipid bilayers containing these oxPCs. Here, we characterize supported lipid bilayers (SLBs) containing POPC, KDdiA-PC, or KOdiA-PC, and cholesterol. We used a quartz crystal microbalance with dissipation monitoring (QCM-D), fluorescence microscopy, and all-atom molecular dynamics (MD) to examine the formation process, biophysical properties, and specific lipid conformations in simulated bilayers. Experimentally, we show that liposomes containing either oxPC form SLBs by rupturing on contact with SiO2 substrates, which differs from the typical adsorption-rupture pathway observed with nonoxidized liposomes. We also show that increasing the oxPC concentration in SLBs results in thinner bilayers that contain defects. Simulations reveal that the oxidized sn-2 tails of KDdiA-PC and KOdiA-PC bend out of the hydrophobic membrane core into the hydrophilic headgroup region and beyond. The altered conformations of these oxPC, which are affected by cholesterol content and protonation state of the oxidized functional groups, contribute to trends of decreasing membrane thickness and increasing membrane area with increasing oxPC concentration. This combined approach provides a comprehensive view of the biophysical properties of membranes containing KDdiA-PC and KOdiA-PC at the molecular level, which is crucial to understanding the role of lipid oxidation in cardiovascular disease and related immune responses.

CHARMM GUI Membrane Builder for oxidized phospholipid membrane modeling and simulation

Oxidative stress leads to the production of oxidized phospholipids (oxPLs) that modulate the biophysical properties of phospholipid monolayers and bilayers. As many immune cells are responsible for surveilling cells and tissues for the presence of oxPLs, oxPL-dependent mechanisms have been suggested as targets for treating chronic kidney disease, atherosclerosis, diabetes, and cancer metastasis. This review details recent experimental and computational studies that characterize oxPLs' behaviors in various monolayers and bilayers. These studies investigate how the tail length and polar functional groups of OxPLs impact membrane properties, how oxidized membranes can be stabilized, and how membrane integrity is generally affected by oxidized lipids. In addition, for oxPL-containing membrane modeling and simulation, CHARMM-GUI Membrane Builder has been extended to support a variety of oxPLs, accelerating the simulation system building process for these biologically relevant lipid bilayers.

Light-Activated Synthetic Rotary Motors in Lipid Membranes Induce Shape Changes Through Membrane Expansion

Membranes are the key structures to separate and spatially organize cellular systems. Their rich dynamics and transformations during the cell cycle are orchestrated by specific membrane-targeted molecular machineries, many of which operate through energy dissipation. Likewise, man-made light-activated molecular rotary motors have previously shown drastic effects on cellular systems, but their physical roles on and within lipid membranes remain largely unexplored. Here, the impact of rotary motors on well-defined biological membranes is systematically investigated. Notably, dramatic mechanical transformations are observed in these systems upon motor irradiation, indicative of motor-induced membrane expansion. The influence of several factors on this phenomenon is systematically explored, such as motor concentration and membrane composition., Membrane fluidity is found to play a crucial role in motor-induced deformations, while only minor contributions from local heating and singlet oxygen generation are observed. Most remarkably, the membrane area expansion under the influence of the motors continues as long as irradiation is maintained, and the system stays out-of-equilibrium. Overall, this research contributes to a comprehensive understanding of molecular motors interacting with biological membranes, elucidating the multifaceted factors that govern membrane responses and shape transitions in the presence of these remarkable molecular machines, thereby supporting their future applications in chemical biology.

Fabrication, modification and application of lipid nanotubes

The potential application of high aspect-ratio nanomaterials motivates the development of the fabrication and modification of lipid nanotubes(LNTs). To date, diverse fabricate processes and elaborate template procedures have produced suitable tubular architectures with definite dimensions and complex structures for expected functions and applications. Herein, we comprehensively summarize the fabrication of LNTs in vitro and discuss the progress made on the micro/nanomaterials fabrication using LNTs as a template, as well as the functions and possible application of a wide range of LNTs as fundamental or derivative material. In addition, the characteristics, advantages, and disadvantages of different fabrication, modification methods, and development prospects of LNTs were briefly summarized.

Lipid nanotubes: Formation and applications

Lipids, the fundamental components of cell membrane, play important roles in the whole cycle of cell life, thus attracting worldwide attention, owing to their physicochemical property and extensive use in the applications based on lipid assemblies. Compared with liposomes, lipid nanotubes (LNTs) usually possess unique properties, such as highly ordered structure, precise molecular recognition, and the possibility of substance transport, thus providing more potential applications in different research fields. However, until now, there are still quite rare cases of LNTs successfully employed in practical applications. Bearing this in mind and based on our own experience in this field, we summarized and discussed the recent progress of the fabrication approaches and representative applications of the LNTs in the past decade, which would potentially provide basic understanding and guidance towards their future development.

Single-molecule phospholipase A2 becomes processive on melittin-induced membrane deformations

While it is established that the topology of lipid membranes plays an important role in biochemical processes, few direct observations exist regarding how the membranes are actively restructured and its consequences on subsequent reactions. In this work, we investigated how the two major components of bee venom, melittin and phospholipase A₂ (PLA₂), achieve activation by such membrane remodeling. Their membrane-disrupting functions have been reported to increase when both are present, but the mechanism of this synergism had not been established. Using membrane reconstitution, we found that melittin can form large-scale membrane deformities upon which PLA₂ activity is 25-fold higher. Tracking of single-molecule PLA₂ revealed that its processive behavior on these deformities underlies the enhanced activity. These results show how melittin and PLA₂ work synergistically to enhance the lytic effects of the bee venom. More broadly, they also demonstrate how the membrane topology may be actively altered to modulate cellular membrane-bound reactions.

Fabrication of Lipid Nanotubules by Ultrasonic Drag Force

This work reports a new method of fabricating lipid nanotubules using ultrasonic Stokes drag force in theory and experiment. Ultrasonic Stokes drag force generated using a planar piezoelectric ultrasonic transducer in a remotely controllable way is introduced. When ultrasonic Stokes drag force is applied on lipid vesicles, the lipid nanotubules attached can be dragged out from the lipid film. In order to demonstrate the formation mechanism of the lipid nanotubules produced by ultrasonic drag force clearly, a theoretical kinetic model is developed. In the experiments, the lipid nanotubules can be rapidly and efficiently fabricated using this ultrasonic transducer both in deionized water and NaCl solutions with different concentrations. The stretching speed of the lipid nanotubules can reach 33 μm/s, approximately 10 times faster than that of the existing methods. The formed lipid nanotubules have a diameter of 600 ± 100 nm (>80%). The length can reach the millimeter level. This work provided a remotely controllable, highly efficient, high-velocity, and solution environment-independent approach for fabricating lipid nanotubules.