Adhesion of K88ab to guinea pig erythrocytes: effect on membrane enzyme activities

Two specific sites for binding of K88ab Escherichia coli fimbriae to porcine intestinal brush border membranes

We have studied the characteristics of the binding of the K88ab Escherichia coli fimbrial antigen to porcine brush border membranes by solid phase binding assay. Binding of biotinylated K88ab to brush border membranes followed a sigmoidal dependence and was saturable, apparent saturation occurring with 0.8 ng of fimbriae (approx. 7 ng of fimbriae per microg of brush border protein) irrespective of incubation temperature in the range of room temperature to 4 degrees C. A Hill plot of log [(fimbriae bound)/(maximal binding-fimbriae bound)] vs. log free fimbriae gave a maximal slope of about 2, indicating the existence of two binding sites. From an analysis of an Scatchard plot, apparent binding constants (1)K(2) and (2)K(2) of 7.1 x 10(8) and 17.1 x 10(8)M(-1) were obtained at room temperature. Nor did temperature have any effect on the rate of binding or on receptor affinity (S(0.5)).

Binding characteristics of purified Escherichia coli K88ab fimbriae to guinea pig erythrocyte membrane

The characteristics of the binding of biotinylated E. coli K88ab fimbriae to guinea pig erythrocyte membranes, as a possible model of the target host cell were studied. Binding showed sigmoidal dependence, with an apparent saturation at about 0.8 ng of fimbriae. Hill coefficient values (h) were about 2-2.4, which indicated that the receptor population showed positive cooperativity with at least three binding sites. Apparent binding constants to the first and third binding sites (1K3 and 3K3) were determined. Three K88ab binding proteins, of 67, 63 and 48 kDa, were identified on solubilized erythrocyte membranes and were recovered mainly in a detergent phase, suggesting a possible integral localization of the receptors.