Abstract
BackgroundHollow vesicles formed from block copolymers, so-called polymersomes, have been extensively studied in the last decade for their various applications in drug delivery, in diagnostics and as nanoreactors. The immobilization of proteins on the polymersomes’ surface can aid in cell targeting, lead to functional biosensors or add an additional reaction space for multistep syntheses. In almost all surface functionalization strategies to date, a chemical pre-conjugation of the polymer with a reactive group or ligand and the functionalization of the protein are required. To avoid chemical pre-conjugation, we investigated the simple and quick functionalization of preformed poly(2-methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyloxazoline) (PMOXA-PDMS-PMOXA) polymersomes through the spontaneous insertion of four hydrophobic, non-antibacterial peptide anchors into the membrane to display enhanced green fluorescent protein (eGFP) on the polymersomes’ surface.ResultsThree of the four hydrophobic peptides, the transmembrane domains of a eukaryotic cytochrome b5, of the viral lysis protein L and of the yeast syntaxin VAM3 could be recombinantly expressed as soluble eGFP-fusion proteins and spontaneously inserted into the polymeric membrane. Characterization of the surface functionalization revealed that peptide insertion was linearly dependent on the protein concentration and possible at a broad temperature range of 4–42 °C. Up to 2320 ± 280 eGFP molecules were immobilized on a single polymersome, which is in agreement with the calculated maximum loading capacity. The peptide insertion was stable without disrupting membrane integrity as shown in calcein leakage experiments and the functionalized polymersomes remained stable for at least 6 weeks.ConclusionThe surface functionalization of polymersomes with hydrophilic proteins can be mediated by several peptide anchors in a spontaneous process at extremely mild insertion conditions and without the need of pre-conjugating polymers.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-016-0205-x) contains supplementary material, which is available to authorized users.
Highlights
Hollow vesicles formed from block copolymers, so-called polymersomes, have been extensively studied in the last decade for their various applications in drug delivery, in diagnostics and as nanoreactors
For the determination of the insertion behavior of the non-antibacterial peptide anchors Cytb5′, L′, Vam3p′ and PolyAL and their ability to immobilize protein on PMOXA15-PDMS68-PMOXA15 membranes, each peptide anchor was genetically fused to enhanced green fluorescent protein (eGFP)
In this study, we demonstrated that the hydrophobic, non-antibacterial peptide anchors Cytb5′, L′ and Vam3p′ readily insert into preformed PMOXA15-PDMS68PMOXA15 polymersomes in a similar manner to the various membrane proteins [20, 22, 23, 25, 26] and antibacterial peptides [26, 27, 29, 30] that have been incorporated into polymer membranes in the recent years
Summary
Hollow vesicles formed from block copolymers, so-called polymersomes, have been extensively studied in the last decade for their various applications in drug delivery, in diagnostics and as nanoreactors. To avoid chemical pre-conjugation, we investigated the simple and quick functionalization of preformed poly(2methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyloxazoline) (PMOXA-PDMS-PMOXA) polymersomes through the spontaneous insertion of four hydrophobic, non-antibacterial peptide anchors into the membrane to display enhanced green fluorescent protein (eGFP) on the polymersomes’ surface. Block copolymers made of hydrophilic and hydrophobic blocks are capable of spontaneously forming hollow vesicles, so called polymersomes, when added to aqueous solutions. Due to their strong resemblance to liposomes [1] and their versatility, polymersomes have been studied for medical applications as drug delivery systems [2,3,4] or biosensors [5] or for biochemical applications as nano-scale membrane reactors [6, 7]. These characteristics allow retaining encapsulated drugs or enzymes within the vesicles, while the low protein binding properties are required to evade the immune system or prevent unspecific protein adsorption to the polymersomes’ surface
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