title: Two successive calcium-dependent transitions mediate membrane binding and oligomerization of daptomycin and the related antibiotic A54145.
abstract: Daptomycin and A54145 are homologous lipopeptide antibiotics that permeabilize the cell membranes of Gram-positive bacteria. Membrane permeabilization depends on the presence of both phosphatidylglycerol (PG) and calcium, and it involves the formation of oligomeric transmembrane pores that consist of approximately 6-8 subunits. We here show that each lipopeptide molecule binds two calcium ions in separable, successive steps. The first calcium ion causes the lipopeptide molecule to bind to the target membrane, and likely to form a loosely associated oligomer. Higher calcium concentrations induce binding of a second ion, which produces the more tightly associated and more deeply membrane-inserted final, functional form of the oligomer. Both calcium-dependent steps are accompanied by fluorescence signals that indicate transition of specific amino acid residues into less polar environments, suggestive of insertion into the target membrane. Our findings agree with the earlier observation that two of the four acidic amino acid residues in the daptomycin molecule are essential for antibacterial activity.
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo N2L 3G1, Ontario, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Taylor
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo N2L 3G1, Ontario, Canada.
authors.forename: Khalida
authors.initials: K
authors.lastname: Butt
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo N2L 3G1, Ontario, Canada.
authors.forename: Bradley
authors.initials: B
authors.lastname: Scott
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo N2L 3G1, Ontario, Canada.
authors.forename: TianHua
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, University of Al-Muthanna, Samawah, Al-Muthanna, Iraq.
authors.forename: Jawad K
authors.initials: JK
authors.lastname: Muraih
authors.affiliation: Department of Chemistry and Physics, Lander College of Arts and Sciences, Touro College, 1602 Ave. J, Brooklyn, NY 11230, United States.
authors.forename: Evan
authors.initials: E
authors.lastname: Mintzer
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo N2L 3G1, Ontario, Canada. Electronic address: s5taylor@uwaterloo.ca.
authors.forename: Scott
authors.initials: S
authors.lastname: Taylor
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo N2L 3G1, Ontario, Canada. Electronic address: mpalmer@uwaterloo.ca.
authors.forename: Michael
authors.initials: M
authors.lastname: Palmer
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D017576:Daptomycin / Q000737:chemistry*; D008074:Lipoproteins / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry*
chemical_list: C065208:A54145; D000900:Anti-Bacterial Agents; D008074:Lipoproteins; D008081:Liposomes; D017576:Daptomycin; D002118:Calcium
keywords: Antibiotics; Calorimetry; Fluorescence; Lipid membranes; Lipopeptides