Zhang, TianHuaTaylor, Scott D.Palmer, MichaelDuhamel, Jean2017-04-212017-04-212016-09-20https://doi.org/10.1016/j.bpj.2016.07.018http://hdl.handle.net/10012/11715The final publication is available at Elsevier via http://doi.org/10.1016/j.bpj.2016.07.018 © 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/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.enAttribution-NonCommercial-NoDerivatives 4.0 InternationalExcimer fluorescenceSolvent polaritiesPy ScaleDaptomycinPolymerModelMacromoleculesAssociationTransitionsInhibitionArticle