Influence Of The Bilayer Composition On The Membrane-Disruption Effect Of Polybia-MP1, A Mastoparan Peptide With Antimicrobial And Leukemic Cell Selectivity

Abstract

Unlike other mastoparans, Polybia-MP1 (IDWKKLLDAAKQIL), from the venom Polybia paulista (wasp), is highly selective for bacterial cells. By flow cytometry, we also found out this selective behavior: Polybia-MP1 promoted a decrease of 60 % cell viability at 25 μM in Jurkat (leukemic) cells, while it was not altered in primary human lymphocytes. The mechanism of selectivity was studied in the interaction with different bilayers. Ion channel-like activity was detected at 0.12 μM peptide concentration with anionic lipid membranes of azolectin, showing conductance in the range of 250 pS. On zwitterionic diphytanoylphosphatidylcholine-(DPhPC) it required 0.18 μM for the same conductance level. Further experiments with DPhPC bilayers containing 30% phophatidylserine or cardiolipin required higher peptide concentration to induce single channel events at slightly lower conductance levels. However, the presence of 20 mol% cholesterol in the mixture significantly reduced the ion channel-like activity, dropped the average conductance to around 120 pS and required 0.30 μM. On vesicles the activity of Polybia-MP1 also shows greater rate of leakage on the anionic over the zwitterionic, impaired by the presence of cholesterol; the lytic activity is characterized by a threshold peptide to lipid molar ratio that depends on the phospholipid composition. Preliminary results of changes in DPH anisotropy and acrylamide quenching of Trp fluorescence show a slight decrease in the anisotropy, and a significant quenching of the Trp fluorescence, indicating small influence on the lipid packing associated to preferential interaction with the lipid head group region. Results suggest that the selectivity of Polybia-MP1 is a consequence of a shallow interaction with zwitterionic bilayers, favored by the presence and position of negatively charged Asp residues, which is not possible for other mastoparan peptides.Support: CAPES, CNPq, FAPESP