title: Model membrane approaches to determine the role of calcium for the antimicrobial activity of friulimicin.
abstract: Friulimicin is a cyclic lipopeptide antibiotic, currently in clinical development, that possesses excellent activity against Gram-positive bacteria, including multiresistant strains. A recent study on the mode of action of friulimicin reported on the interference with bacterial cell wall biosynthesis via a calcium-dependent complexing of the bactoprenol phosphate carrier C₅₅-P. The calcium dependency of this non-common targeted activity remains to be elucidated. In the present model membrane approach, the role of calcium for friulimicin targeting to C₅₅-P was investigated by biosensor-based detection of binding affinities. The findings were supplemented by atomic force microscopy (AFM) and circular dichroism (CD) spectroscopy. Comparing the calcium salt of friulimicin with the calcium-free peptide, calcium appeared to be essential for friulimicin interaction with DOPC model membranes. The binding affinity was even higher in the presence of 0.1 mol% C₅₅-P (0.21 μM vs. 1.22 μM), confirming the targeted mode of action. Binding experiments with supplemented calcium salts suggest (i) the phosphate group as the essential moiety of C₅₅-P, referring to a bridging function of calcium between the negatively charged friulimicin and C₅₅-P, and (ii) a structural effect of calcium shifting the peptide into a suitable binding conformation (CD spectra). AFM images confirmed that calcium has no, or only a minor, effect on the aggregate formation of friulimicin. These data shed new light on the mechanisms of antibacterial activity of friulimicin.
authors.affiliation: Department of Pharmacy, Rheinische Friedrich-Wilhelms-Universität Bonn, An der Immenburg 4, 53121 Bonn, Germany. kchrist@uni-bonn.de
authors.forename: Katrin
authors.initials: K
authors.lastname: Reder-Christ
authors.forename: Hildegard
authors.initials: H
authors.lastname: Falkenstein-Paul
authors.forename: Gabriela
authors.initials: G
authors.lastname: Klocek
authors.forename: Saad
authors.initials: S
authors.lastname: Al-Kaddah
authors.forename: Udo
authors.initials: U
authors.lastname: Bakowsky
authors.forename: Gerd
authors.initials: G
authors.lastname: Bendas
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides; D015374:Biosensing Techniques; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry; D002473:Cell Wall / Q000187:drug effects* / Q000378:metabolism; D002942:Circular Dichroism; D055808:Drug Discovery; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000378:metabolism; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D010455:Peptides / Q000494:pharmacology*; D011106:Polyisoprenyl Phosphates / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D013057:Spectrum Analysis
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D010455:Peptides; D011106:Polyisoprenyl Phosphates; C416817:friulimicin A; C000119:bactoprenylpyrophosphate; D002118:Calcium