Interaction Force Fluctuations in Antigen–Antibody Biorecognition Studied by Atomic Force Spectroscopy

The formation of a specific complex between β2μglobulin and antiβ2μglobulin was investigated by analyzing the force fluctuations recorded in an atomic force spectroscopy biorecognition experiment. We found that a 1/f noise appears in the power spectra of force fluctuations when the tip, functionalized with β2μglobulin, reaches a distance of 0.50 nm from the partner-charged substrate while a specific biorecognition process occurs. Concomitantly, in this active region, the distribution of the times spent by the tip in the proximity of the substrate exhibits a power law trend characterized by a long-time tail. All of these findings are put into relationship to a slowing down of the energy landscape exploration, consistent with a restricted sampling dynamics of the conformational states driving to the final binding state. The hypothesis that a combination of a conformational substrate and an induced fit hybrid binding mechanism controls the specific complex formation is put forward and discussed also in connection with the fluctuations of the hydration water network.