Soutenance de thèse : Marta SALVADOR CASTELL
Apolar lipids: the membrane adaptation toolbox of extremophiles
Doctorante : Marta SALVADOR CASTELL
Laboratoire INSA : MAP
Ecole doctorale : ED341 Evolution Ecosystèmes Microbiologie Modélisation
Most of Earth’s biotopes are under extreme environmental conditions, e.g. distant from the optimal life conditions for humans. Nevertheless, a large biological diversity of organisms, the extremophiles, inhabit such environments. For instance, organisms living at deep-sea hydrothermal vents experience temperatures above 100°C, high concentrations of reduced metals, the absence of oxygen and high hydrostatic pressures. To date, there is no understanding of the molecular mechanisms enabling them to sustain such extreme conditions. The cell membrane is particularly sensitive to external conditions, but at the same time must maintain specific physical properties, such as fluidity and permeability, to preserve the integrity and functionality of the cell. This thesis work seeks to understand how the lipid bilayer can remain functional at high temperatures and high pressures and thus can allow life under extreme conditions.
This work establishes novel membrane components, apolar lipids from the polyisoprenoid’s family, which play the role of membrane regulators and confer stability to the lipid bilayer, along with dynamism and heterogeneity, which are essential properties for an optimal function of the membrane. Apolar lipids are localized in the midplane of the lipid bilayer and adjust membrane curvature and permeability. Because of such specific localization, apolar lipids reduce proton membrane permeability at high hydrostatic pressures. They establish functional domains with differentiated functions that could favour the insertion of specific membrane proteins and hence could enable essential cell functions that require highly curved membrane domains, such as fusion and fission. All these results demonstrate experimentally a novel cell membrane architecture for extremophiles in which the presence and the quantity of polyisoprenoids play a key role in cell membrane adaptation and constitute a novel adaptation route to extreme conditions applicable to the origin of life.
Amphithéâtre Emilie du Châtelet - Bibliothèque Marie Curie - INSA Lyon