Structural Characterization of an Archaeal Lipid Bilayer as a Function of Hydration and Temperature.

Marta Salvador-Castell,Bruno Demé,Judith Peters,Philippe Oger

doi:10.3390/ijms21051816

Abstract

Archaea, the most extremophilic domain of life, contain ether and branched lipids which provide extraordinary bilayer properties. We determined the structural characteristics of diether archaeal-like phospholipids as functions of hydration and temperature by neutron diffraction. Hydration and temperature are both crucial parameters for the self-assembly and physicochemical properties of lipid bilayers. In this study, we detected non-lamellar phases of archaeal-like lipids at low hydration levels, and lamellar phases at levels of 90% relative humidity or more exclusively. Moreover, at 90% relative humidity, a phase transition between two lamellar phases was discernible. At full hydration, lamellar phases were present up to 70 °C and no phase transition was observed within the temperature range studied (from 25 °C to 70 °C). In addition, we determined the neutron scattering length density and the bilayer’s structural parameters from different hydration and temperature conditions. At the highest levels of hydration, the system exhibited rearrangements on its corresponding hydrophobic region. Furthermore, the water uptake of the lipids examined was remarkably high. We discuss the effect of ether linkages and branched lipids on the exceptional characteristics of archaeal phospholipids.

Highlights

The archaea domain consists of unicellular microorganisms that have adapted to withstand extreme conditions, such as high temperatures, high hydrostatic pressures, and outermost pH values
We used a mixture of DoPhPC:di-Of-oprmhyutnailnamyle-llsanr -vgesliyclcees r[1o3-]3. -phosphoethanolamine (DoPhPE) (9:1, mol:mol), which are synthetic archaeal lipids with characteristics similar to natural archaeal monopolar lipids
As observed on the Neutron scattering length density (NSLD), the change in hydration of the sample caused a rearrangement of its hydrophobic region consisting of the hydrocarbon chains

Summary

Introduction

The archaea domain consists of unicellular microorganisms that have adapted to withstand extreme conditions, such as high temperatures, high hydrostatic pressures, and outermost pH values. All these environments represent a stress for the non-adapted organisms. High temperatures would lead to an unstable, unreasonably permeable cell membrane and the loss of the physicochemical properties of the functional lipid phase. To sustain these extreme conditions, phospholipids that assemble the archaeal membranes are unique and differ from usual bacterial lipids. Both phytanyl chains and ether linkages impact the physicochemical properties of lipids

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Conclusion