Lipid Analysis Concentrating on Graphene Oxide

A study team (Professor Ryugo Tero et al.) from the Department of Applied Chemistry and Life Sciences at Toyohashi University of Technology discovered the phenomenon in which certain lipids concentrate on graphene oxide in a multicomponent lipid bilayer membrane that acts as a model cell membrane.

This group of studies also elucidates the mechanism by which constituents of “lipid rafts” (where significant cell membrane reactions such as metabolism and nerve transmission occur) assemble due to the surface characteristics of graphene oxide. This breakthrough is expected to be used in the basic technology for separating and concentrating lipids and membrane proteins in cell membranes as a major research target in the drug discovery and medicine field.

Details

The transfer of information, substances, and energy needed for life activities both inside and outside the cell is carried out through the cell membrane. Such exchanges are heavily involved in metabolism, nerve transmission, and viral infection, which makes them significant research targets in medicine, biology, and drug discovery.

The lipid bilayer membrane is the basic structure of the cell membrane. Certain membrane proteins and lipids assemble by lateral diffusion and aggregation of molecules within the membrane. These areas are known as lipid domains, which in turn regulate and increase the efficiency of reactions that occur in the cell membrane.

The “lipid raft” is one typical example of a lipid domain, which is rich in cholesterol and sphingolipids. New technologies for arranging and positioning of lipid domains on solid substrates are demanded for screening and biosensing of membrane proteins and lipids.

This study group fabricated an artificial lipid bilayer on graphene oxide monolayers deposited on a silicon substrate. They discovered for the first time that the lipid domains are concentrated in graphene oxide. Graphene oxide has a structure in which the hydrophilic oxygen functional group belongs to graphene (monatomic carbon sheet material).

In a two-component lipid bilayer consisting of two types of phosphatidylcholine with varying fluidity, most of the low-fluidity gel phase domains in the lipid bilayer membrane are aggregated on graphene oxide. Many components of the lipid rafts exist in graphene oxide in the lipid bilayer membrane of a three-component mixture of cholesterol, sphingolipids, and phosphatidylcholine.

Regardless of the lipid composition, the less liquid lipid domains cluster on graphene oxide. This is due to the presence of a mixture of hydrophilic and hydrophobic regions on the graphene oxide surface at the nanometer scale. The initial process of domain formation in the lipid bilayer occurs preferentially in the hydrophobic regions of graphene oxide.

Professor Ryugo Tero, Research Team Leader, Toyohashi University of Technology

Future Outlook

The research group anticipates that control of the position of lipid domains on solid substrates is applicable to regulating membrane proteins using a high affinity for those lipids in the same position. This breakthrough is valuable for fundamental technologies in the fields of biosensing and targeting membrane proteins.

Moreover, the study group hopes that the same approach can be used to collect biochemically significant lipid components such as glycolipids and lipid rafts. They hope this will be valuable in the development of techniques to purify and concentrate rare lipids and membrane proteins in cell membranes.

Journal Reference

Tero, R. et al. (2023). Domain Localization by Graphene Oxide in Supported Lipid Bilayers. International Journal of Molecular Sciences. dx.doi.org/10.3390/ijms24097999.

Source: https://www.tut.ac.jp/english/