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

• Published in: Biochimica et biophysica acta 2014-03, Vol.1838 (3), p.842-852
• Main Authors: Suárez-Germà, Carme, Domènech, Òscar, Montero, M. Teresa, Hernández-Borrell, Jordi
• Format: Article
• Language: English
• Subjects: AFM; Lactose permease; Lateral segregation; Lipid Bilayers - chemistry; Lipid Bilayers - metabolism; Mechanical Phenomena; Membrane Transport Proteins - metabolism; Microscopy, Atomic Force; Nanotechnology; Phosphatidylethanolamines - chemistry; Phosphatidylglycerols - chemistry; Phospholipids; Proteolipids - chemistry
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/j.bbamem.2013.11.015

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). Both compositions displayed phase separation and were investigated by atomic force microscopy (AFM) imaging and force-spectroscopy (FS) mode. PLSs displayed two separated, segregated domains with different features that were characterised by FS and force-volume mode. We correlated the nanomechanical characteristics of solid-like gel phase (Lβ) and fluid liquid-crystalline phase (Lα) with phases emerging in presence of LacY. We observed that for both compositions, the extended PLSs showed a Lβ apparently formed only by lipids, whilst the second domain was enriched in LacY. The influence of the lipid environment on LacY organisation was studied by performing protein unfolding experiments using the AFM tip. Although the pulling experiments were unspecific, positive events were obtained, indicating the influence of the lipid environment when pulling the protein. A possible influence of the lateral surface pressure on this behaviour is suggested by the higher force required to pull LacY from DPPE:POPG than from POPE:POPG matrices. This is related to higher forces governing protein–lipid interaction in presence of DPPE. [Display omitted] •Separated phases are formed by supported lipid bilayers of POPE:POPG and DPPE:POPG.•Topographical and force spectroscopy allows to discriminate between both phases.•Lactose permease of Escherichia coli is reconstituted in POPE:POPG and DPPE:POPG.•Nanomechanics of lipid phases are affected by the presence of lactose permease.•The influence of the lipid composition on lactose permease pulling has been studied.