How arginine derivatives alter the stability of lipid membranes: dissecting the roles of side chains, backbone and termini

Arginine (R)-rich peptides constitute the most relevant class of cell-penetrating peptides and other membrane-active peptides that can translocate across the cell membrane or generate defects in lipid bilayers such as water-filled pores. The mode of action of R-rich peptides remains a topic of controversy, mainly because a quantitative and energetic understanding of arginine effects on membrane stability is lacking. Here, we explore the ability of several oligo-arginines R$$_n$$ n and of an arginine side chain mimic R$$_\mathrm {Side}$$ Side to induce pore formation in lipid bilayers employing MD simulations, free-energy calculations, breakthrough force spectroscopy and leakage assays. Our experiments reveal that R$$_\mathrm {Side}$$ Side but not R$$_n$$ n reduces the line tension of a membrane with anionic lipids. While R$$_n$$ n peptides form a layer on top of a partly negatively charged lipid bilayer, R$$_\mathrm {Side}$$ Side leads to its disintegration. Complementary, our simulations show R$$_\mathrm {Side}$$ Side causes membrane thinning and area per lipid increase beside lowering the pore nucleation free energy. Model polyarginine R$$_8$$ 8 similarly promoted pore formation in simulations, but without overall bilayer destabilization. We conclude that while the guanidine moiety is intrinsically membrane-disruptive, poly-arginines favor pore formation in negatively charged membranes via a different mechanism. Pore formation by R-rich peptides seems to be counteracted by lipids with PC headgroups. We found that long R$$_n$$ n and R$$_\mathrm {Side}$$ Side but not short R$$_n$$ n reduce the free energy of nucleating a pore. In short R$$_n$$ n , the substantial effect of the charged termini prevent their membrane activity, rationalizing why only longer $$\mathrm {R}_{n}$$ R n are membrane-active.