Direct Transmembrane Interaction between Actin and the Pore-Competent, Cholesterol-Dependent Cytolysin Pneumolysin

Abstract

The eukaryotic actin cytoskeleton is an evolutionarily well-established pathogen target, as a large number of bacterial factors disturb its dynamics to alter the function of the host cells. These pathogenic factors modulate or mimic actin effector proteins or they modify actin directly, leading to an imbalance of the precisely regulated actin turnover. Here, we show that the pore-forming, cholesterol-dependent cytolysin pneumolysin (PLY), a major neurotoxin of Streptococcus pneumoniae, has the capacity to bind actin directly and to enhance actin polymerisation in vitro. In cells, the toxin co-localised with F-actin shortly after exposure, and this direct interaction was verified by Förster resonance energy transfer. PLY was capable of exerting its effect on actin through the lipid bilayer of giant unilamellar vesicles, but only when its pore competence was preserved. The dissociation constant of G-actin binding to PLY in a biochemical environment was 170–190 nM, which is indicative of a high-affinity interaction, comparable to the affinity of other intracellular actin-binding factors. Our results demonstrate the first example of a direct interaction of a pore-forming toxin with cytoskeletal components, suggesting that the cross talk between pore-forming cytolysins and cells is more complex than previously thought.

Phobalysin, a Small β-Pore-Forming Toxin of Photobacterium damselae subsp. damselae

“…S2D in the supplemental material) might affect epithelial integrity and possibly change adhesive properties (58,59). Interestingly, direct interaction between a PFT and actin has been reported (60). Sustained attenuation of translation via inactivation of mTORC1 and/or hyperphosphorylation of eIF2␣ will ultimately lead to cell death (45,61).…”

Mini-Review: Novel Therapeutic Strategies to Blunt Actions of Pneumolysin in the Lungs

“…A recent study reported that PLY binds cellular actin with high affinity, an activity that is dependent on the pore forming capacity of the toxin [57]. The same research group also showed that the toxin is internalized after binding to the cell membrane, indicating a repair mechanism that allows cells to withstand and recover from toxin concentrations that are not immediately lytic [57].…”

“…The same research group also showed that the toxin is internalized after binding to the cell membrane, indicating a repair mechanism that allows cells to withstand and recover from toxin concentrations that are not immediately lytic [57]. …”

Pneumolysin

“…At sublytic concentrations Ply has several effects on eukaryotic cell signaling. While domains 1, 2, and 3 and full-length Ply bind strongly to actin, the nonlytic deletion mutant has reduced binding activity, suggesting that the refolding and/or conformational changes that occur in domains 1 to 3 during pore formation are required for actin binding [34]. These micropores lead to calcium influx and activation of rac and rho GTPases, including rac-1 and the rho-associated kinase [31].…”