The electric double layer structure modulates poly-dT25 conformation and adsorption kinetics at the cationic lipid bilayer interface

GMP affected assembly behaviors of phosphatidylethanolamine monolayers elucidated by multi-resolved SFG-VS and BAM

The interaction between nucleotide molecules and lipid molecules plays important roles in cell activities, but the molecular mechanism is very elusive. In the present study, a small but noticeable interaction between the negatively charged phosphatidylethanolamine (PE) and Guanosine monophosphate (GMP) molecules was observed from the PE monolayer at the air/water interface. As shown by the sum frequency generation (SFG) spectra and Pi-A isotherm of the PE monolayer, the interaction between the PE and GMP molecules imposes very small changes to the PE molecules. However, the Brewster angle microscopy (BAM) technique revealed that the assembly conformations of PE molecules are significantly changed by the adsorption of GMP molecules. By comparing the SFG spectra of PE monolayers after the adsorption of GMP, guanosine and guanine, it is also shown that the hydrogen bonding effect plays an important role in the nucleotide-PE interactions. These results provide fundamental insight into the structure changes during the nucleotide-lipid interaction, which may shed light on the molecular mechanism of viral infection, DNA drug delivery, and cell membrane curvature control in the brain or neurons.

In situ study of structural changes: Exploring the mechanism of protein corona transition from soft to hard

HYPOTHESIS

The process of protein corona changes has been widely believed to follow the Vroman effect, while protein structural change during the process is rarely reported, due to the lack of analytical methods. In-situ interpretation for protein structural change is critical to processes such as the recognition and transport of nanomaterials.

EXPERIMENTS

Molecular dynamics (MD) simulation was used to predict the deflection and twist of the protein tertiary structure. The structural changes of the surface protein corona during the interaction of nanoparticles (NPs) with lipid bilayer were probed in situ and real-time by sum frequency generation (SFG) spectroscopy.

FINDINGS

The ring tertiary structure of the protein corona is altered from vertical to horizontal on particle surface, a process of the soft-to-hard structural transition, which is contributed by the hydrogen bonding force between the protein and water molecules. The negatively charged protein corona can induce the redistribution of interfacial charge, leading to a more stable hydrogen bond network of the interfacial water. Our findings suggest that the structural change from flexible to rigid is a crucial process in the soft-to-hard transition of the protein corona, which will be a beneficial supplement to the Vroman effect of protein adsorption.

Magnesium Ion Responses of Zwitterionic Phosphatidylethanolamine Head and Tail Groups Elucidated by Frequency-Resolved SFG-VS

In the present study, the effects of magnesium ions on the conformational changes of the deuterated 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (D₅₄-DMPE) monolayer were elucidated by frequency-resolved sum frequency generation vibrational spectroscopy (SFG-VS) and surface pressure-area isotherm measurements. It is found that the tilt angles of the methyl in tail groups decrease, while the tilt angles of the phosphate and methylene in head groups increase during the compression of the DMPE monolayers at both the air/water interface and the air/MgCl₂ solution interfaces. It is also shown that the tilt angle of the methyl in the tail groups slightly decreases, while the tilt angles of the phosphate and methylene in the head groups significantly increase as the MgCl₂ concentration increases from 0 to 1.0 M. These results indicate that both the tail groups and the head groups of the DMPE molecules become closer to the surface normal, as the MgCl₂ concentration increases in the subphase.

Binding affinity and conformation of a conjugated AS1411 aptamer at a cationic lipid bilayer interface

Aptamers have been widely used in the detection, diagnosis, and treatment of cancer. Owing to their special binding affinity toward cancer-related biomarkers, aptamers can be used for targeted drug delivery or bio-sensing/bio-imaging in various scenarios. The interfacial properties of aptamers play important roles in controlling the surface charge, recognition efficiency, and binding affinity of drug-delivering lipid-based carriers. In this research, the interfacial behaviors, such as surface orientation, molecular conformation, and adsorption kinetics of conjugated AS1411 molecules at different cationic lipid bilayer interfaces were investigated by sum frequency generation vibrational spectroscopy (SFG-VS) in situ and in real-time. It is shown that the conjugated AS1411 molecules at the DMTAP bilayer interface show a higher binding affinity but with slower binding kinetics compared to the DMDAP bilayer interface. The analysis results also reveal that the thymine residues of cholesteryl conjugated AS1411 molecules show higher conformational ordering compared to the thymine residues of the alkyl chain conjugated AS1411 molecules. These understandings provide unique molecular insight into the aptamer-lipid membrane interactions, which may help researchers to improve the efficiency and safety of aptamer-related drug delivery systems.

Revealing local molecular distribution, orientation, phase separation, and formation of domains in artificial lipid layers: Towards comprehensive characterization of biological membranes

Lipids, together with molecules such as DNA and proteins, are one of the most relevant systems responsible for the existence of life. Selected lipids are able to assembly into various organized structures, such as lipid membranes. The unique properties of lipid membranes determine their complex functions, not only to separate biological environments, but also to participate in regulatory functions, absorption of nutrients, cell-cell communication, endocytosis, cell signaling, and many others. Despite numerous scientific efforts, still little is known about the reason underlying the variability within lipid membranes, and its biochemical significance. In this review, we discuss the structural complexity of lipid membranes, as well as the importance to simplify studied systems in order to understand phenomena occurring in natural, complex membranes. Such systems require a model interface to be analyzed. Therefore, here we focused on analytical studies of artificial systems at various interfaces. The molecular structure of lipid membranes, specifically the nanometric thickens of molecular bilayer, limits in a major extent the choice of highly sensitive methods suitable to study such structures. Therefore, we focused on methods that combine high sensitivity, and/or chemical selectivity, and/or nanometric spatial resolution, such as atomic force microscopy, nanospectroscopy (tip-enhanced Raman spectroscopy, infrared nanospectroscopy), phase modulation infrared reflection-absorption spectroscopy, sum-frequency generation spectroscopy. We summarized experimental and theoretical approaches providing information about molecular structure and composition, lipid spatial distribution (phase separation), organization (domain shape, molecular orientation) of lipid membranes, and real-time visualization of the influence of various molecules (proteins, drugs) on their integrity. An integral part of this review discusses the latest achievements in the field of lipid layer-based biosensors.