title: Utilizing zeta potential measurements to study the effective charge, membrane partitioning, and membrane permeation of the lipopeptide surfactin.
abstract: The effective charge of membrane-active molecules such as the fungicidal lipopeptide surfactin (SF) is a crucial property governing solubility, membrane partitioning, and membrane permeability. We present zeta potential measurements of liposomes to measure the effective charge as well as membrane partitioning of SF by utilizing what we call an equi-activity analysis of several series of samples with different lipid concentrations. We observe an effective charge of -1.0 for SF at pH8.5 and insignificantly lower at pH7.4, illustrating that the effective charge may deviate strongly from the nominal value (-2 for 1 Asp, 1 Glu). The apparent partition coefficient decreases from roughly 100 to 20/mM with increasing membrane content of SF in agreement with the literature. Finally, by comparing zeta potentials measured soon after the addition of peptide to liposomes with those measured after a heat treatment to induce transmembrane equilibration of SF, we quantified the asymmetry of partitioning between the outer and inner leaflets. At very low concentration, SF binds exclusively to the outer leaflet. The onset of partial translocation to the inner leaflet occurs at about 5mol-% SF in the membrane. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College st, Toronto, ON M5S3M2, Canada.
authors.forename: Helen Y
authors.initials: HY
authors.lastname: Fan
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College st, Toronto, ON M5S3M2, Canada.
authors.forename: Mozhgan
authors.initials: M
authors.lastname: Nazari
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College st, Toronto, ON M5S3M2, Canada.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Raval
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College st, Toronto, ON M5S3M2, Canada.
authors.forename: Zubeir
authors.initials: Z
authors.lastname: Khan
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College st, Toronto, ON M5S3M2, Canada.
authors.forename: Hiren
authors.initials: H
authors.lastname: Patel
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College st, Toronto, ON M5S3M2, Canada; Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany. Electronic address: heiko.heerklotz@utoronto.ca.
authors.forename: Heiko
authors.initials: H
authors.lastname: Heerklotz
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects*; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry; D055666:Lipopeptides / Q000737:chemistry* / Q000494:pharmacology; D008081:Liposomes / Q000737:chemistry; D008564:Membrane Potentials / Q000187:drug effects; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000494:pharmacology; D012995:Solubility
chemical_list: D023181:Antimicrobial Cationic Peptides; D008051:Lipid Bilayers; D055666:Lipopeptides; D008081:Liposomes; D010456:Peptides, Cyclic; C009365:surfactin peptide
keywords: Antimicrobial; Lipopeptide; Membrane partitioning; Membrane permeation; Zeta potential