QUARTZ-CRYSTAL MICROBALANCE INVESTIGATION OF THE INTERACTION OF BACTERIAL TOXINS WITH GANGLIOSIDE CONTAINING SOLID SUPPORTED MEMBRANES

The binding of cholera toxin, tetanus toxin and pertussis toxin to gan glioside containing solid supported membranes has been investigated by quartz crystal microbalance measurements. The bilayers were prepared by fusion of phospholipid-vesicles on a hydrophobic monolayer of octan ethiol chemisorbed on one gold electrode placed on the 5 MHz AT-cut qu artz crystal. The ability of the gangliosides G(M1), G(M3), G(D1a), G( D1b), G(T1b) and asialo-G(M1) to act as suitable receptors for the dif ferent toxins was tested by measuring the changes of quartz resonance frequencies. To obtain the binding constants of each ligand-receptor-c ouple Langmuir-isotherms were successfully fitted to the experimental adsorption isotherms. Cholera toxin shows a high affinity for G(M1) (K -a=1.8 . 10(8)M(-1)), a lower one for asialo-G(M1) (K-a=1.0.10(7) M-1) and no affinity for G(M3). The C-fragment of tetanus toxin binds to g anglioside G(D1a), G(D1b) and G(T1b) containing membranes with similar affinity (K-a similar to 10(6) M-1), while no binding was observed wi th G(M3). Pertussis toxin binds to membranes containing the gangliosid e G(D1a) with a binding constant of K-a = 1.6.10(6) M-1, but only if l arge amounts (40 mol%) of G(D1a) are present. The maximum frequency sh ift caused by the protein adsorption depends strongly on the molecular structure of the receptor. This is clearly demonstrated by an observe d maximum frequency decrease of 99 Hz for the adsorption of the C-frag ment of tetanus toxin to G(D1b) In contrast to this large frequency de crease, which was unexpectedly high with respect to Sauerbrey's equati on, implying pure mass loading, a maximum shift of only 28 Hz was dete cted after adsorption of the C-fragment of tetanus toxin to G(D1a).