This little plant Arabidopsis thaliana was used in the study to modelize lipid repartition within the cell.
A team of the Plant Reproduction and Development laboratory (RDP– Université de Lyon, ENS de Lyon, Université Claude Bernard Lyon 1, CNRS, INRA) just found that certain lipid species power an electrostatic field that controls protein localization at the cell surface. This work, published in the July issue of the journal Nature Plants, addresses a central question in biology: what are the mechanisms controlling the geography of cell?
Proteins have specific localization within the cell, which contributes to their activity. For example, they can be localized in the nucleus to regulate gene expression, in the mitochondria to produce energy, or at the cell surface to control cell-to-cell communication. How proteins are targeted to different cellular territories is a key question in the cell biology of every organism, whether it is a bacterium, a human or a plant.
In eukaryotes, each cellular compartment is surrounded by a lipid bilayer called the membrane. These membranes have specific lipid compositions, which are recognized by proteins and allow their targeting toward the different cellular territories. In order to study the lipid repartition within the cell, the Cell Signaling and Endocytosis group of the RDP used the model plant Arabidopsis thaliana.
While mapping the localization of different lipid species, the team discovered that a specific category of lipid resides preferentially at the cell surface, a cellular territory called the plasma membrane. Interestingly, these lipids have a common and rare characteristic for a lipid; they are negatively charged, suggesting that they might provide electrostatic properties to the plasma membrane. To test this hypothesis, the researchers developed fluorescent probes that react to the strength of the membrane electrostatic field. This experiment confirmed that the plasma membrane is indeed highly electronegative. Furthermore, they proved that each membrane carries a specific charge signature, which allows the specific localization of proteins.
Next, the team asked why some proteins are sensitive to the membrane electrostatic field while others are not. By comparing these two types of proteins, the researchers identified a “hook” sequence, which tethers proteins at the cell surface. This sequence is also charged, but this time is highly positive. Proteins with the electropositive hook sequence are attracted by the electronegative plasma membrane, while proteins lacking the hook are not.
This work shows that membrane identity may be regulated by charges carried by the lipids. This is a relatively simple system that resembles the “lock and key” model, however it allows tremendous possibility of regulation. Indeed, cellular activities may rapidly modify the “key”, by modulating the lipid species at the plasma membrane, or the “lock”, by changing the charge property of the hook sequence. This work opens new fields of research aiming at understanding how the membrane electrostatic field is set up and maintained and how it may vary during cell division and differentiation.

Références : Simon MLA, Platre MP, Marquès-Bueno MM, Armengot L, Stanislas T, Bayle V, Caillaud MC and Jaillais Y. 2016. A PtdIns(4)P-driven electrostatic field controls cell membrane identity and signaling in plants. Nature Plants.16089 | DOI: 10.1038/NPLANTS.2016.89