Combined force spectroscopy, AFM and calorimetric studies to reveal the nanostructural organization of biomimetic membranes.

In this work we studied a binary lipid matrix of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG), a composition that mimics the inner membrane of Escherichia coli. More specifically, liposomes with varying fractions of POPG were analysed by differential scanning calorimetry (DSC) and a binary phase diagram of the system was created. Additionally, we performed atomic force microscopy (AFM) imaging of supported lipid bilayers (SLBs) of similar compositions at different temperatures, in order to create a pseudo-binary phase diagram specific to this membrane model.

Modeling FRET to investigate the selectivity of lactose permease of Escherichia coli for lipids.

Förster resonance energy transfer (FRET) is a photophysical process by which a donor (D) molecule in an electronic excited state transfers its excitation energy to a second species, the acceptor (A). Since FRET efficiency depends on D-A separation, the measurement of donor fluorescence in presence and absence of the acceptor allows determination of this distance, and therefore FRET has been extensively used as a "spectroscopic ruler". In membranes, interpretation of FRET is more complex, since one D may be surrounded by many A molecules.

Effect of lactose permease presence on the structure and nanomechanics of two-component supported lipid bilayers.

In this paper we present a comparative study of supported lipid bilayers (SLBs) and proteolipid sheets (PLSs) obtained from deposition of lactose permease (LacY) of Escherichia coli proteoliposomes in plane. Lipid matrices of two components, phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), at a 3:1, mol/mol ratio, were selected to mimic the inner membrane of the bacteria. The aim was to investigate how species of different compactness and stiffness affect the integration, distribution and nanomechanical properties of LacY in mixtures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) or 1,2-palmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) with 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG).

Phospholipid-lactose permease interaction as reported by a head-labeled pyrene phosphatidylethanolamine: a FRET study.

Förster resonance energy transfer (FRET) measurements were performed in preceding works to study the selectivity between a single-tryptophan mutant of lactose permease (LacY) of Escherichia coli (used as the donor) and phospholipid probes labeled with pyrene at the acyl chain moiety (used as the acceptor). In the present work, we report the results obtained by using the same LacY mutant (W151/C154G) and binary lipid mixtures of phosphatidylethanolamine (PE) differing in the acyl chain composition and 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG) (3:1 mol/mol) doped with a phospholipid probe labeled with pyrene at the headgroup. The use of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(1-pyrenesulfonyl) ammonium salt (HPyr-PE), which bears two unsaturated acyl chains, enabled the investigation of the specific interaction between LacY and HPyr-PE.

Phosphatidylethanolamine-lactose permease interaction: a comparative study based on FRET.

In this work we have investigated the selectivity of lactose permease (LacY) of Escherichia coli (E. coli) for its surrounding phospholipids when reconstituted in binary mixtures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1,2-Palmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), or 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) with 1-palmitoyl-2-oleoyl-sn-glycero-3-(phospho-rac-(1-glycerol)) (POPG). Förster resonance energy transfer (FRET) measurements have been performed to investigate the selectivity between a single tryptophan mutant of LacY used as donor (D), and two analogues of POPE and POPG labeled with pyrene in the acyl chains (Pyr-PE and Pyr-PG) used as acceptors.