Cationic Copolymer‐Chaperoned 2D–3D Reversible Conversion of Lipid Membranes

Abstract

Reversible conversion between planar nanosheets and 3D structures in response to specific triggers would enable construction of nanodevices with useful electronic, optical, mechanical, biological, and surface properties. Here, we describe controlled formation, stabilization, and 2D-3D conversion of noncanonical planer lipid nanosheets. The lipid nanosheets were generated from vesicles by the addition of mixture of amphiphilic peptides and cationic copolymers having peptide-chaperoning activity. By refining the copolymer structure, autonomous and reversible conversion between 2D nanosheets and cell-sized 3D vesicles in response to triggers, such as pH and enzymatic activity, was achieved.We have reported that a cationic graft copolymer with a polycation backbone and water soluble graft chains has chaperone-like activity toward DNA [6] and peptides. [7] Poly(allylamine)-graft-dextran (PAA-g-Dex, Figure 1a) activates membrane-disruptive acidic peptide, E5, by facilitating folding of the peptide into an active amphiphilic helical conformation ( Figure 1b). E5 chaperoned by the copolymer had considerably higher membrane-disruptive activity than that observed for E5 alone. [7] To understand the effect of the copolymer and E5 on lipid membrane, a suspension of fluorescent-labeled vesicles was incubated with E5, PAA-g-Dex having 92 wt% dextran, or their mixture under physiological salt and pH conditions (10 × 10 −3 m HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid)-NaOH (pH 7.4), 140 × 10 −3 m NaCl). The addition of E5/PAA-g-Dex caused a change from circles to lines in confocal microscopic images ( Figure 1c,d and Figure S4, Supporting Information), suggesting that the spherical vesicle structure was changed to a sheet structure. 3D image reconstructed from z-stack images also suggested morphological change from vesicle to sheet by E5/PAA-g-Dex ( Figure S5, Supporting Information). From the images, we calculated fraction of nanosheet (number of nanosheets/number of all lipid assemblies × 100). Most vesicles (92%, n > 300) were converted to the sheet structure within 5 min of E5/PAA-g-Dex addition. Previously, mesoscale nanosheet structures were observed by the addition of proteins having FERM domain, [8] which are cytoskeletal proteins, to lipid vesicles. However, the efficiency of conversion to the nanosheet structure induced by the proteins Nanosheets have thicknesses on the order of nanometers and planar dimensions in the micrometer range. Nanomaterials that are capable of converting reversibly between 2D nanosheets and 3D structures in response to specific triggers can enable construction of nanodevices. Supra-molecular lipid nanosheets and their triggered conversions to 3D structures including vesicles and cups are reported. They are produced from lipid vesicles upon addition of amphiphilic peptides and cationic copolymers that act as peptide chaperones. By regulation of the chaperoning activity of the copolymer, 2D to 3D conversions are reversibly triggered, allowing tuning of lipid bilayer structures an...

Autonomous Vesicle/Sheet Transformation of Cell-Sized Lipid Bilayers by Hetero-Grafted Copolymers

“…To investigate the effect of dextran content on the conversion of lipid vesicles to nanosheets, the E5 peptide (0–10 μM) and 6.9 μM PAA- g -Dex (600 μM of amino group) were added to giant vesicles of DOPC in 10 mM HEPES (pH 7.4) containing 140 mM NaCl, and the samples were evaluated using fluorescence confocal microscopy observation (Figure c). In the confocal microscopic images, spherical vesicles appear as circles, and nanosheets are observed as lines or planer images due to their orientation . The fraction of nanosheet was calculated from the observed images as number of nanosheets divided by the number of all lipid assemblies.…”

“…In the confocal microscopic images, spherical vesicles appear as circles, and nanosheets are observed as lines or planer images due to their orientation. 19 The fraction of nanosheet was calculated from the observed images as number of nanosheets divided by the number of all lipid assemblies. Without the E5 peptide (i.e., [E5] = 0 μM), the lipid membranes remained as vesicles in the presence of the copolymers.…”

“…In the course of our attempts to control structure and function of peptides with ionic graft copolymers, , we accidentally found that cell-sized lipid vesicles are quantitatively transformed to mesoscopic lipid bilayer nanosheets with high efficiency upon addition of the amphiphilic E5 peptide and a cationic comb-type copolymer (Figure ). The E5 peptide is an anionic membrane-disruptive peptide that mimics the N-terminal region of hemagglutinin . Poly­(allylamine)- graft -dextran (PAA- g -Dex), a cationic copolymer composed of a cationic backbone and dense grafts of hydrophilic dextran (92 wt %), forms a water-soluble inter-polyelectrolyte nanoassembly with E5.…”

Artificial Molecular Chaperone Systems for Proteins, Nucleic Acids, and Synthetic Molecules

“…More recently, a fascinating example reported by Maruyama and co-workers involved a molecular system that chaperoned the conversion of spherical lipid vesicles into 2D bilayer membrane sheets (Figure ). The system was composed of a membrane-disruptive acidic peptide called E5 and a cationic copolymer, poly­(allylamine)- graft -dextran (PAA- g -Dex). PAA- g -Dex aided the folding of E5 into a helical structure.…”

“…(b) Fluorescence microscopy images of a giant liposome with the E5 peptide after addition of PAA- g -Dex at 0, 3.1, 5.5, 9.4, and 11.6 s. (c) Schematic illustration of a proposed model for the formation of a stable lipid bilayer nanosheet at the edge. Reproduced with permission . Copyright 2019, Wiley-VCH.…”