The Lipopeptide Antibiotic Friulimicin B Inhibits Cell Wall Biosynthesis through Complex Formation with Bactoprenol Phosphate

Abstract

Friulimicin B is a naturally occurring cyclic lipopeptide, produced by the actinomycete Actinoplanes friuliensis, with excellent activity against gram-positive pathogens, including multidrug-resistant strains. It consists of a macrocyclic decapeptide core and a lipid tail, interlinked by an exocyclic amino acid. Friulimicin is water soluble and amphiphilic, with an overall negative charge. Amphiphilicity is enhanced in the presence of Ca²⁺, which is also indispensable for antimicrobial activity. Friulimicin shares these physicochemical properties with daptomycin, which is suggested to kill gram-positive bacteria through the formation of pores in the cytoplasmic membrane. In spite of the fact that friulimicin shares features of structure and potency with daptomycin, we found that friulimicin has a unique mode of action and severely affects the cell envelope of gram-positive bacteria, acting via a defined target. We found friulimicin to interrupt the cell wall precursor cycle through the formation of a Ca²⁺-dependent complex with the bactoprenol phosphate carrier C₅₅-P, which is not targeted by any other antibiotic in use. Since C₅₅-P also serves as a carrier in teichoic acid biosynthesis and capsule formation, it is likely that friulimicin blocks multiple pathways that are essential for a functional gram-positive cell envelope.