Carbohydrate-carbohydrate interactions in biological systems have recently been recognized as important for cell-cell interactions such as cell-adhesion, proliferation, differentiation as well as for disease processes such as tumour formation and metastasis. In this project, focus is on the last example. Metastasis of melanoma cells, which is initiated by their binding to the endothelium, is directed via the specific interaction between sialosylllactosylceramid (GM3) and gangliotriaosylcermaide (Gg3). The existence of this interaction has been a matter of debate due to the very weak interaction strength. However, strong and specific interaction can be realized via the formation of so called lipid raft domains into which the glycolipids become concentrated. This concentration enables multivalent interaction and the raft domains act as communicating and signalling hubs. We are investigating the formation of raft domains containing GM3 in models of the extracellular leaflet using mainly Langmuir monolayers-based techniques (FRET, GIXD, IRRAS, surface pressure-area/time isotherms and dilatational rheology). More specifically, IRRAS has been used as a non-invasive method to conveniently follow the formation of the raft domains by probing the methylene stretch vibration of the hydrophobic lipid chains. The binding of Gg3-containing liposomes to monolayers or bilayers containing GM3 is studied using TIRF spectroscopy and SPR. As a complement, the biological relevance is investigated by cell-binding assays (flow cytometry and confocal fluorescence microscopy) and signal transduction (Western Blot) using GM3 and Gg3 expressing cell-lines (murine melanoma B16 and lymphoma L5178-S cells lines respectively).
