Direct measurement of recognition forces between proteins and membrane receptors

The interactions between the protein, cholera toxin B subunit attached to a n atomic force microscope, AFM, cantilever, CTB and its receptor the gangli oside, GM(1) have been measured in a dilute electrolyte solution, pH 5.5. A lthough there is variation in the force separation data obtained, particula rly on approach of the AFM tip to the GM(1) surface where usually, but not always an attraction is noted, an adhesion is always noted on separation of the surfaces. The strength of this adhesion varies from experiment to expe riment, but appears to be quantised at a value of around 90 pN. Addition of cholera toxin to the aqueous electrolyte solution completely removes the a ttractive interaction and adhesion. This gives us confidence that in the ea rlier experiments, a specific interaction between the CTB and GM(1) was mea sured.