Charakterisierung der Eigenschaften rekonstituierterplanarer Membranen und deren Änderung durch porenbildende Proteine mit Hilfe von elektrischen und optischen Methoden
The lipid matrix of the outer membrane of Gram-negative bacteria is an asymmetric bilayer composed of a phospholipid inner leaflet and a lipopolysaccharide (LPS) outer leaflet. In the present study, electrical and optical measurements on a planar reconstitution system of these membranes were performed to show the influence of the composition of the lipidmatrix on properties and functions of the membrane – on the one hand as a matrix, in which bacterial membrane proteins are embedded, and on the other hand as a barrier for antimicrobial peptides of the immune system of the host. The focus was mainly directed on the role of LPS, in particular the structure of its sugar moiety and its net negative charge. It could be shown exemplarily for the phosphoporin from Echerichia coli that LPS – in particular the structure of the sugar moiety – has a strong influence on the pore formation by porins. In general, the pore formation rate increased with increasing length of the sugar moiety of LPS. Furthermore, it could be shown for a cationic antimicrobial peptide of the cathelicidin family that a reduction of the net negative charge of LPS by positively charged sugar groups leads to a decrease of the electrostatic interaction between the peptide and LPS and, thus, causing a reduction of the accumulation and/or intercalation of the peptide. A very remarkable result was obtained from first fluorescence microscopic experiments on the reconstitution system of the outer membrane: domains, which were clearly visible in the LPS-monolayer, disappear after adding the opposing phospholipid-monolayer, indicating a strong interaction between both side of the lipid bilayer.
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