Cationic Graft Copolymer as a DNA B-Z Transition Inducer: Effect of Copolymer Structure

Spatially regulated activation of membrane fusogenic peptides with chaperone-like ionic copolymers

Controlled or targeted membrane lysis induced by cascades of assembly and activation of biomolecules on membrane surfaces is important in programmed cell death and host defense systems. In a previous study, we reported that an ionic graft copolymer with a polycation backbone and water-soluble graft chains, poly(allylamine)-graft-dextran (PAA-g-Dex) chaperoned folding and assembly of E5, a membrane-destructive peptide derived from influenza hemagglutinin, to its increase membrane-disruptive activity. In this study, we modified the copolymer with long acyl chains, which resulted in delivery of the copolymer to membrane surfaces of liposomes and living cells. The liposomes with PAA-g-Dex functionalized with stearic acid (PAA-g-Dex-SA) on their surfaces underwent vesicle-to-sheet conversion upon addition of E5, whereas control liposomes did not. E5 also induced selective lysis of cells incubated with PAA-g-Dex-SA. The spatially specific activation of E5 on target membrane surfaces driven by self-assembly of copolymer and activation of E5 should find application in lipid-based delivery devices and cell-based therapeutics.

Cationic copolymer-chaperoned short-armed 10-23 DNAzymes

The cationic copolymer poly(L-lysine)-graft-dextran (PLL-g-Dex) has nucleic acid chaperone-like activity. The copolymer facilitates both DNA hybridization and strand exchange reactions. For these reasons, DNA-based enzyme (DNAzyme) activity is enhanced in the presence of copolymer. In this study, we evaluated activities of DNAzymes with substrate-binding arms (S-arms) of various lengths. The copolymer promoted DNAzyme reactivity and turnover efficacy, and, depending on S-arm length, maximally accelerated the reaction rate by 250-fold compared to the rate in the absence of copolymer. The copolymer permitted up to six nucleotides truncation of the S-arms having initial length of 10 and 11 nucleotides without loss of catalytic efficiency, enable tuning of the optimal temperature ranging from 30 to 55 °C. The approach might be useful for the development of DNAzyme systems targeting short or highly structured RNAs as well for improvement of DNAzyme-based nanomachines and biosensors.

Inter-polyelectrolyte nano-assembly induces folding and activation of functional peptides

Insufficient solubility, fragile folding structure and short half-life frequently hamper use of peptides as biological reagents or therapies. To enhance the peptide function, the effect of complexation of the peptides with ionic graft copolymers with water-soluble graft chains was tested in this study. Amphiphilic anionic peptide E5 acquires membrane disrupting activity at acidic pH due to folding from the random coil state to an ordered α-helical structure. Aggregation and imprecise folding of the peptide limited membrane disrupting activity of the peptide. In the presence of a cationic graft copolymer, E5 and its analogs adopted an ordered conformation without aggregation. The mixture of the peptides and the copolymer functioned more efficiently than peptide alone at not only acidic pH but also neutral pH at which the peptide alone had no activity. Similarly, a cationic peptide was successfully folded and activated by an anionic graft copolymer. Thus, our analysis indicated that spontaneous nano-assembly of ionic peptides with graft copolymers having opposite ionic charges triggers the folding of peptides without loss of solubility, leading to enhanced bioactivity.

DNA strand exchange reaction activated by cationic comb-type copolymers having ureido groups

Ureido modification of cationic graft copolymers accelerated DNA strand exchange reaction relative to unmodified copolymers.