Toward a Membrane-Centric Biology

Peptide-lipid hybrid vesicles with stimuli-responsive phase separation for controlled membrane functions

A disulfide-tethered peptide-lipid conjugate self-assembled into a homogeneously distributed peptide-lipid hybrid vesicle. Upon dithiothreitol treatment, the homogeneous peptide-lipid membrane spontaneously divided into lipid-rich and peptide-rich domains, while the vesicle retained its size and shape. Membrane phase separation enhanced temperature-dependent cargo release.

Low Concentrations of Oxidized Phospholipids Increase Stress Tolerance of Endothelial Cells

Oxidized phospholipids (OxPLs) are generated by enzymatic or autooxidation of esterified polyunsaturated fatty acids (PUFAs) residues. OxPLs are present in circulation and atherosclerotic plaques where they are thought to induce predominantly proinflammatory and toxic changes in endothelial (ECs) and other cell types. Unexpectedly, we found that low concentrations of OxPLs were not toxic but protected ECs from stress induced by serum deprivation or cytostatic drugs. The protective effect was observed in ECs obtained from different vessels and was monitored using a variety of readouts based on different biological and chemical principles. Analysis of the structure−activity relationship identified oxidized or missing fatty acid residue (OxPLs or Lyso-PLs, respectively) as a prerequisite for the protective action of a PL. Protective OxPLs or Lyso-PLs acquired detergent-like properties and formed in solution aggregates <10 nm in diameter (likely micelles), which were in striking contrast with large aggregates (>1000 nm, likely multilayer liposomes) produced by nonoxidized precursor PLs. Because surfactants, OxPLs, and Lyso-PLs are known to extract membrane cholesterol, we tested if this effect might trigger the protection of endothelial cells. The protective action of OxPLs and Lyso-PLs was inhibited by cotreatment with cholesterol and mimicked by cholesterol-binding beta-cyclodextrin but not inactive α-cyclodextrin. Wide-scale mRNA expression analysis in four types of ECs showed the induction of genes encoding for heat shock proteins (HSPs) and secreted prosurvival peptides and proteins. Inducers of HSPs, chemical chaperones, and pure prosurvival factors mimicked the protective action of OxPLs/Lyso-PLs. We hypothesize that oxidation changes the physicochemical properties of PLs, thus promoting membrane cholesterol redistribution or extraction leading to the expression of intra- and extracellular prosurvival factors.

N-(3-Oxododecanoyl) Homoserine Lactone Is a Generalizable Plasma Membrane Lipid-Ordered Domain Modifier

A mammalian plasma membrane is a structure on which several layers of complexity are built. The first order of complexity comes from the heterogeneity of lipid-ordered domains. Gangliosides in concert with cholesterol are preferentially packed on the outer leaflet and form lipid-ordered domains, commonly known as lipid rafts. The formation and dynamics of these domains impact nearly all membrane protein functions and are an intensely studied topic. However, tools suited for lipid domain alteration are extremely limited. Currently, methyl-β-cyclodextrin (MβCD) appears to be the most common way to disrupt lipid domains, which is believed to operate via cholesterol extraction. This significantly limits our ability in membrane biophysics research. Previously, we found that N-(3-oxo-dodecanoyl) homoserine lactone (3oc), a small signaling chemical produced by Pseudomonas aeruginosa, is highly efficient in altering lipid-ordered domains. In this study, 3oc was compared with MβCD in a series of biochemical, biophysical, and cell biological analyses. Per molarity, 3oc is more efficient than MβCD in domain alteration and appears to better retain membrane lipids after treatment. This finding will provide an essential reagent in membrane biophysics research.

Membrane Rafts: Portals for Viral Entry

Membrane rafts are dynamic, small (10-200 nm) domains enriched with cholesterol and sphingolipids that compartmentalize cellular processes. Rafts participate in roles essential to the lifecycle of different viral families including virus entry, assembly and/or budding events. Rafts seem to participate in virus attachment and recruitment to the cell surface, as well as the endocytic and non-endocytic mechanisms some viruses use to enter host cells. In this review, we will introduce the specific role of rafts in viral entry and define cellular factors implied in the choice of one entry pathway over the others. Finally, we will summarize the most relevant information about raft participation in the entry process of enveloped and non-enveloped viruses.