title: Structural properties of archaeal lipid bilayers: small-angle X-ray scattering and molecular dynamics simulation study.
abstract: Aeropyrum pernix is an aerobic hyperthermophilic archaeon that grows in harsh environmental conditions and as such possesses unique structural and metabolic features. Its membrane interfaces with the extreme environment and is the first line of defense from external factors. Therefore, lipids composing this membrane have special moieties that increase its stability. The membrane of A. pernix is composed predominantly of two polar lipids 2,3-di-O-sesterterpanyl-sn-glicerol-1-phospho-1'(2'-O-α-D-glucosyl)-myo-inositol (AGI) and 2,3-di-O-sesterterpanyl-sn-glicerol-1-phospho-myo-inositol (AI). Both have methyl branches in their lipid tails and ether linkages and carbohydrates in their headgroup. These moieties significantly affect the structure and dynamics of the bilayer. To provide a molecular level insight into these characteristics, we used here Molecular Dynamics (MD) simulations of lipid bilayers of composition similar to those of the archaeal membranes. First, we show that the electron density profiles along the normal to the bilayers derived from the simulations are in good agreement with the profiles obtained by the small-angle X-ray scattering (SAXS) technique, which provides confidence in the force fields used. Analyses of the simulation data show that the archaeal lipid bilayers are less hydrated than conventional phosphatidylcholine (PC) lipids and that their structure is not affected by the salt present in the surrounding solution. Furthermore, the lateral pressure in their hydrophobic core, due to the presence of the branched tails, is much higher than that at PC-based lipid bilayers. Both the methyl branched tails and the special headgroup moieties contribute to slow drastically the lateral diffusion of the lipids. Furthermore, we found that the lipid head groups associate via hydrogen bonding, which affects their reorientational dynamics. All together, our data provide links between the microscopic properties of these membranes and their overall stability in harsh environments.
authors.affiliation: Faculty of Electrical Engineering, University of Ljubljana , Tržaška cesta 25, SI-1000 Ljubljana, Slovenia.
authors.forename: Andraž
authors.initials: A
authors.lastname: Polak
authors.forename: Mounir
authors.initials: M
authors.lastname: Tarek
authors.forename: Matija
authors.initials: M
authors.lastname: Tomšič
authors.forename: Janez
authors.initials: J
authors.lastname: Valant
authors.forename: Nataša Poklar
authors.initials: NP
authors.lastname: Ulrih
authors.forename: Andrej
authors.initials: A
authors.lastname: Jamnik
authors.forename: Peter
authors.initials: P
authors.lastname: Kramar
authors.forename: Damijan
authors.initials: D
authors.lastname: Miklavčič
mesh_terms: D001105:Archaea / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D053838:Scattering, Small Angle
chemical_list: D008051:Lipid Bilayers