title: Membrane Binding and Oligomerization of the Lipopeptide A54145 Studied by Pyrene Fluorescence.
abstract: A54145 is a lipopeptide antibiotic related to daptomycin that permeabilizes bacterial cell membranes. Its action requires both calcium and phosphatidylglycerol in the target membrane, and it is accompanied by the formation of membrane-associated oligomers. We here probed the interaction of A54145 with model membranes composed of dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol, using the steady-state and time-resolved fluorescence of a pyrene-labeled derivative (Py-A54145). In solution, the labeled peptide was found to exist as a monomer. Its membrane interaction occurred in two stages that could be clearly distinguished by varying the calcium concentration. In the first stage, which was observed between 0.15 and 1 mM calcium, Py-A54145 bound to the membrane, as indicated by a strong increase in pyrene monomer emission. At the same calcium concentration, excimer emission increased also, suggesting that Py-A54145 had oligomerized. A global analysis of the time-resolved pyrene monomer and excimer fluorescence confirmed that Py-A54145 forms oligomers quantitatively and concomitantly with membrane binding. When calcium was raised beyond 1 mM, a distinct second transition was observed that may correspond to a doubling of the number of oligomer subunits. The collective findings confirm and extend our understanding of the action mode of A54145 and daptomycin.
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada.
authors.forename: TianHua
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Taylor
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada. Electronic address: mpalmer@uwaterloo.ca.
authors.forename: Michael
authors.initials: M
authors.lastname: Palmer
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada. Electronic address: jduhamel@uwaterloo.ca.
authors.forename: Jean
authors.initials: J
authors.lastname: Duhamel
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology; D001412:Bacillus subtilis / Q000187:drug effects; D002118:Calcium / Q000737:chemistry; D002413:Cations, Divalent / Q000737:chemistry; D017576:Daptomycin / Q000737:chemistry / Q000494:pharmacology; D019281:Dimerization; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D008074:Lipoproteins / Q000737:chemistry / Q000494:pharmacology; D008081:Liposomes / Q000737:chemistry*; D008962:Models, Theoretical; D015394:Molecular Structure; D010715:Phosphatidylglycerols / Q000737:chemistry; D011721:Pyrenes / Q000737:chemistry; D012996:Solutions; D013057:Spectrum Analysis; D014867:Water / Q000737:chemistry
chemical_list: C065208:A54145; D000900:Anti-Bacterial Agents; D002413:Cations, Divalent; D005456:Fluorescent Dyes; D008074:Lipoproteins; D008081:Liposomes; D010715:Phosphatidylglycerols; D011721:Pyrenes; D012996:Solutions; D014867:Water; C030984:pyrene; C002773:dimyristoylphosphatidylglycerol; D017576:Daptomycin; D002118:Calcium; D004134:Dimyristoylphosphatidylcholine