| Abstract
| - The present study determines the affinity of cholera toxin for theganglioside series GM1,GM2, GM3, GD1A, GD1B, GT1B, asialo GM1, globotriosyl ceramide, andlactosyl ceramide using realtime biospecific interaction analysis (surface plasmon resonance, SPR).SPR shows that cholera toxinpreferably binds to gangliosides in the following sequence: GM1 >GM2 > GD1A > GM3 > GT1B >GD1B > asialo-GM1. The measured binding affinity of cholera toxinfor the ganglioside sequence rangesfrom 4.61 × 10-12 M for GM1 to 1.88 ×10-10 M for asialo GM1. The picomolar valuesobtained bysurface plasmon resonance are similar to Kdvalues determined with whole-cell binding assays.Bothwhole-cell assays and SPR measurements on synthetic membranes arehigher than free solutionmeasurements by several orders of magnitude. This difference maybe caused by the effects of avidityand charged lipid head-groups, which may play a major role in thebinding between cholera toxin, thereceptor, and the membrane surface. The primary difference betweenfree solution binding studies andsurface plasmon resonance studies is that the latter technique isperformed on surfaces resembling thecell membrane. Surface plasmon resonance has the further advantageof measuring apparent kineticassociation and dissociation rates in real time, providing directinformation about binding events at themembrane surface.
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