Kalata B1 and Kalata B2 Have a Surfactant-Like Activity in Phosphatidylethanolomine-Containing Lipid Membranes

Abstract

Cyclotides are cyclic disulfide-rich peptides that are chemically and thermally stable and possess pharmaceutical and insecticidal properties. The activities reported for cyclotides correlate with their ability to target phosphatidylethanolamine (PE)-phospholipids and disrupt cell membranes. However, the mechanism by which this disruption occurs remains unclear. In the current study we examine the effect of the prototypic cyclotides, kalata B1 (kB1) and kalata B2 (kB2) on tethered lipid bilayer membranes (tBLMs) using swept frequency electrical impedance spectroscopy. We confirmed that kB1 and kB2 bind to bilayers only if they contain PE-phospholipids. We hypothesize that the increase in membrane conduction and capacitance observed upon addition of kB1 or kB2 is unlikely to result from ion channel like pores, but is consistent with the formation of lipidic toroidal pores. This hypothesis is supported by the concentration dependence of effects of kB1 and kB2 being suggestive of a critical micelle concentration event rather than a progressive increase in conduction arising from increased channel insertion. Additionally, conduction behaviour is readily reversible when the peptide is rinsed from the bilayer. Our results support a mechanism by which kB1 and kB2 bind to and disrupt PE-containing membranes by decreasing the overall membrane critical packing parameter, as would a surfactant, which then opens or increases the size of existing membrane defects. The cyclotides need not participate directly in the conductive pore, but might exert their effect indirectly through altering membrane packing constraints and inducing purely lipidic conductive pores.

An examination of microcystin-LR accumulation and toxicity using tethered bilayer lipid membranes (tBLMs)

“…This response is consistent with a change in membrane packing brought about by the interaction of the microcystin-LR with the lipid bilayer. According to a membrane packing model, this alteration of the membrane packing arrangement causes an increase in the diameter of intrinsic toroidal pores within the membrane and is unlikely to be due to the formation of new pores (Cranfield et al, 2016;Cranfield et al, 2017;Kuppusamy et al, 2018). This data is supported by the fact that there is little change in membrane capacitance as a result of adding 1 µM microcystin-LR ( Figure 4B, D and F).…”

“…cholesterol. POPE and cholesterol are membrane constituents necessary for the interactions of numerous other toxins and peptides with lipid bilayers (Palmer, 2001;Henriques et al, 2011; Al Khamici et al, 2016;Cranfield et al, 2017). For each of the different membranes used there was a consistent increase in membrane conduction due to the presence of 1 µM microcystin-LR ( Figure 4A, C and E).…”

Decoupling the effects of hydrophilic and hydrophobic moieties at the neuron–nanofibre interface

“…This technique has previously been used to assess the activity of various bespoke and natural peptides on lipid bilayers. [51][52][53] Upon addition of 1 and 10 mM solutions of tetrapeptide nanobres, minimal disruption of the membrane bilayer was observed. However, upon treatment of the membranes with 100 mM nanobre solutions, signicant increases in membrane conductance can be seen for Fmoc-FKKF and Fmoc-KFFK ( Fig.…”

“…As determined in the NMR measurements, these membrane interactions are likely due to the increased conformational exibility of the hydrophobic residues of Fmoc-FKKF and Fmoc-KFFK causing alterations in lipid bilayer packing, expanding intrinsic membrane pores, as described previously. 51,53,54 This ability to disrupt the lipid membrane is likely the reason that decreased neuronal viability is seen on substrates of Fmoc-FKKF and Fmoc-KFFK. Fig.…”

Oxytocin receptor agonists and their clinical application

“…Интерес к циклотидам продолжает возрастать. Так, обнаружено [31], что физиологическое действие циклотидов калаты В1 и калаты В2 подобно действию сурфактанта, которое проявляется в снижении поверхностного натяжения в альвеолах легких, что объясняется их способностью взаимодействовать с такими фосфолипидами мембраны, как фосфатидилэтаноламин.…”