Abstract
The modification of archaeal lipid bilayer properties by the insertion of apolar molecules in the lipid bilayer midplane has been proposed to support cell membrane adaptation to extreme environmental conditions of temperature and hydrostatic pressure. In this work, we characterize the insertion effects of the apolar polyisoprenoid squalane on the permeability and fluidity of archaeal model membrane bilayers, composed of lipid analogues. We have monitored large molecule and proton permeability and Laurdan generalized polarization from lipid vesicles as a function of temperature and hydrostatic pressure. Even at low concentration, squalane (1 mol%) is able to enhance solute permeation by increasing membrane fluidity, but at the same time, to decrease proton permeability of the lipid bilayer. The squalane physicochemical impact on membrane properties are congruent with a possible role of apolar intercalants on the adaptation of Archaea to extreme conditions. In addition, such intercalant might be used to cheaply create or modify chemically resistant liposomes (archeaosomes) for drug delivery.
Highlights
Regardless of environmental constraints, Archaea are found to inhabit the most extreme environments on Earth
The main objective of this research is (1) to determine how the apolar polyisoprenoid squalane modifies the fluidity and the permeability to water and protons of an archaeal lipid bilayer mimic and (2) to determine to what extent apolar polyisoprenoids act as membrane regulators in archaea changing their physicochemical properties
The presence of squalane or similar isoprenoid molecules in archaeal membranes suggests that these apolar molecules may play a role in cell membrane adaptation to extreme conditions
Summary
Regardless of environmental constraints (pH, temperature, salinity, etc.), Archaea are found to inhabit the most extreme environments on Earth These organisms are adapted to require severe environmental conditions that otherwise would have fatal effects. High hydrostatic pressures increase the ordering of lipids in the membrane and decrease the fluidity of the lipid hydrocarbon chains [2,3]. Such findings resemble the corresponding state principle for proteins [4] and might indicate that to yield functional organisms, the cell components of both non-extremophiles and extremophiles should harbor similar physicochemical parameters under their optimal growth conditions. A lipid membrane from a hyperthermophile microorganism, such as T. barophilus, which grows optimally at 85 ◦ C, should present a fluidity and permeability at high temperature (ca. 85 ◦ C) similar to that of the membrane of a mesophilic microorganism like Escherichia coli which grows optimally at 37 ◦ C as stipulated by the homeoviscous adaptation theory
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