Interkingdom Signaling: Integration, Conformation, and Orientation of N-Acyl-L-homoserine Lactones in Supported Lipid Bilayers

摘要

N-Acyl-L-homoserine lactones (AHLs) are small cell-to-cell signaling molecules involved in the regulation ofnpopulation density and local gene expression in microbial communities. Recent evidence shows that contact of this signalingnsystem, usually referred to as quorum sensing, to living eukaryotes results in interactions of AHL with host cells in a processntermed “interkingdom signaling”. So far details of this process and the binding site of the AHLs remain unknown; both annintracellular and a membrane-bound receptor seem possible, the first of which requires passage through the cell membrane. Here,nwe used sum-frequency-generation (SFG) spectroscopy to investigate the integration, conformation, orientation, andntranslocation of deuterated N-acyl-L-homoserine lactones (AHL-dn) with varying chain length (8, 12, and 14 C atoms) in lipidnbilayers consisting of a 1:1 mixture of POPC:POPG supported on SiO2 substrates (prepared by vesicle fusion). We found that allnAHL-dn derivatives are well-ordered within the supported lipid bilayer (SLB) in a preferentially all-trans conformation of thendeuterated alkyl chain and integrated into the upper leaflet of the SLB with the methyl terminal groups pointing downward. Fornthe bilayer system described above, no flip-flop of AHL-dn from the upper leaflet to the lower one could be observed. Spectralnassignments and interpretations were further supported by Fourier transform infrared and Raman spectroscopy.