The Synthetic Amphipathic Peptidomimetic LTX109 Is a Potent Fungicide That Disturbs Plasma Membrane Integrity in a Sphingolipid Dependent Manner

The peptidomimetic LTX109 (arginine-tertbutyl tryptophan-arginine-phenylethan) was previously shown to have antibacterial properties. Here, we investigated the activity of this novel antimicrobial peptidomimetic on the yeast Saccharomyces cerevisiae. We found that LTX109 was an efficient fungicide that killed all viable cells in an exponentially growing population as well as a large proportion of cells in biofilm formed on an abiotic surface. LTX109 had similar killing kinetics to the membrane-permeabilizing fungicide amphotericin B, which led us to investigate the ability of LTX109 to disrupt plasma membrane integrity. S. cerevisiae cells exposed to a high concentration of LTX109 showed rapid release of potassium and amino acids, suggesting that LTX109 acted by destabilizing the plasma membrane. This was supported by the finding that cells were permeable to the fluorescent nucleic acid stain SYTOX Green after a few minutes of LTX109 treatment. We screened a haploid S. cerevisiae gene deletion library for mutants resistant to LTX109 to uncover potential molecular targets. Eight genes conferred LTX109 resistance when deleted and six were involved in the sphingolipid biosynthetic pathway (SUR1, SUR2, SKN1, IPT1, FEN1 and ORM2). The involvement of all of these genes in the biosynthetic pathway for the fungal-specific lipids mannosylinositol phosphorylceramide (MIPC) and mannosyl di-(inositol phosphoryl) ceramide (M(IP)2C) suggested that these lipids were essential for LTX109 sensitivity. Our observations are consistent with a model in which LTX109 kills S. cerevisiae by nonspecific destabilization of the plasma membrane through direct or indirect interaction with the sphingolipids

Lipopeptide secondary metabolites from the phytopathogenic bacterium Pseudomonas syringae.

Over the past twenty years or so, significant advances have been made in the study of the secondary metabolism of the widespread phytopathogenic Gram-negative bacterium Pseudomonas syringae. Interdisciplinary approach, which required the expertise of plant pathologists, chemists, biochemists and molecular biologists, led to the discovery of a new family of bioactive peptide secondary metabolites. The determination of their structures was pivotal for the investigations on their biosynthetic pathways, their relevance in the development of plant disease, and for the understanding of the molecular bases of their biological activities in plant, microbial and animal cells. In particular, the antibiotic activities of some of these compounds appear very interesting in the perspective of their utilization both in medicine and in agriculture. The goal of this chapter is to summarize the present knowledge in various areas of research on P. syringae peptide metabolites