Membrane remodeling by the lytic fragment of sticholysin II: implications for the toroidal pore model

Abstract

Sticholysins are pore-forming toxins of biomedical interest and represent a prototype of proteins acting through the formation of protein-lipid or toroidal pores. Peptides spanning the N-terminus of sticholysins can mimic their permeabilizing activity and together with the full-length toxins have been used as a tool to understand the mechanism of pore formation in membranes. However, the lytic mechanism of these peptides and the lipid shape modulating their activity are not completely clear. In this paper, we combine molecular dynamics (MD) simulations and experimental biophysical tools to dissect different aspects of the pore-forming mechanism of StII1-30, a peptide derived from the N-terminus of sticholysin II. With this combined approach, membrane curvature induction and flip-flop movement of the lipids were identified as two important membrane remodeling steps mediated by StII1-30-pore forming activity.Pore-formation by this peptide was enhanced by the presence of the negatively-curved lipid phosphatidylethanolamine (PE) in membranes. This lipid emerged not only as a facilitator of membrane interactions but also as a structural element of the StII1-30-pore that is recruited to the pore ring upon its assembly. Collectively, these new findings support a toroidal model for the architecture of the pore formed by this peptide and provide new molecular insight into the role of PE as a membrane component that easily accommodates into the ring of toroidal pores aiding in its stabilization. This study contributes to a better understanding of the molecular mechanism underlying the permeabilizing activity of StII1-30 and peptides or proteins acting via a toroidal pore mechanism and offers an informative framework for the optimization of the biomedical application of this and similar molecules.

Pore formation in regulated cell death

“…MLKL may act instead as an α‐PFP by inducing membrane curvature without fully spanning the hydrophobic core of the membrane (Fig 5C). A similar mechanism has been proposed for different lytic peptides and proteins such as melittin and magainin (Sengupta et al , 2008; Lee et al , 2011) and actinoporins (Alvarez et al , 2003; Mesa‐Galloso et al , 2019; Fig 5C). In this case, the asymmetric attack of the amphipathic α‐helices of the unfolded 4HB would induce membrane thinning and tension, inducing membrane curvature and toroidal pore formation (Chen et al , 2003; Grage et al , 2016; Woo & Lee, 2017).…”

“…2 MLKL may act instead as an a-PFP by inducing membrane curvature without fully spanning the hydrophobic core of the membrane (Fig 5C ). A similar mechanism has been proposed for different lytic peptides and proteins such as melittin and magainin (Sengupta et al, 2008;Lee et al, 2011) and actinoporins (Alvarez et al, 2003;Mesa-Galloso et al, 2019;Fig 5C).…”