Lipodepsipeptides (LDPs) are a group of cyclic, acylated peptides produced by Pseudomonas syringae, a plant pathogenic bacterium with a wide host range which includes economically important crops. On the basis of their amino acidic chain length they are usually divided into two groups called mycins and peptins. Mycins have a ring of 9 amino acids closed between the first and the last residue, peptins contain a more complex peptide moiety of up to 25 amino acid, partially cyclized. LDPs significantly contribute to bacterial pathogenesis. Their primary site of action is the plasma membrane, but may have different target organisms. Peptins are stronger phytotoxins with less antifungal activity than the mycins. Therefore mycins could potentially be useful for the development of agents for the control of plant and human diseases. Here, we describe a biophysical characterization of the interaction of these two groups of LDPs with model membranes. We focused our attention syringomycin E (SRE) and syringopeptin 25A (SP25A), which are supposed to be good model for the two groups. We investigated the architecture of the pore formed by LDPs in lipid by determining the transmembrane movement of a fluorescent lipid included in the bilayer, by the method of extraction of a short chain lipid by BSA. The amount of labeled lipid extracted by BSA in the external compartment was increased by the subsequent addition of SP25A. The peptin promotes the transfer of lipids from the inner to the outer layer. This is a clear indication of the formation of a toroidal pore, which puts the inner and outer layer in contact. Instead SRE behavior was dependent on the lipid composition: the transfer of the fluorescent lipid from the inner to the outer layer was seen only in the presence of sphingomyelin. FTIR was used to assess changes of the secondary structure when the SP25A goes from the buffer solution to the membrane. The peptine orientation, when absorbed into the lipid matrix, was measured by polarized ATR-FTIR. The experiments showed an increase in the helical content of SP25A after absorption into the membrane. The orientation of the peptin alfahelical fraction showed an angle of 27 with respect to the lipid acyl chains, suggesting that SP25A is not laying on the membrane surface but instead is inserted into the lipid core.
|Number of pages||2|
|Publication status||Published - 22 Jun 2005|
|Event||Matter, Materials and Devices - Edificio Magazzini del Cotone - Via ai Magazzini del Cotone - Area Porto Antico, Genova, Italy|
Duration: 22 Jun 2005 → 25 Jun 2005
|Conference||Matter, Materials and Devices|
|Period||22/06/05 → 25/06/05|
|Other||MMD-Meeting is the National Conference of the Italian scientific community that is active in the broad field of Matter, Materials and Devices. It is promoted jointly by three national research institutions: CNR (with its "Dipartimento Materiali e Dispositivi"), CNISM, and INFM.|
The conference will emphasize interdisciplinary research and especially the contribution of young scientists and students, thus continuing the tradition of the previous INFM-meeting series. "Young Authors Awards" will be offered to the best posters selected by the Program Committee.
Plenary Sessions, parallel Topical Sessions, and Poster Sessions will run from Wednesday, June 22, to Friday, June 24, 2005. The morning of Saturday, June 25, will offer a space for discussions on the status, perspectives, and organization of research.