Abstract
Antibody, which is one of the most important proteins for adaptive immunity, has been well studied. In our previous studies, we showed the changes of antigen recognition mechanisms during antibody evolution and the structure changes of antibody with antigen-binding using thermodynamic and kinetic measurements. Since these structure changes were considered extremely small, we investigated the structural fluctuations of a single antibody molecule in real-time and space using a Diffracted X-ray Tracking method with pm-level accuracy. We found that the structural fluctuations of Fab fragments were various on each antibody clone and were suppressed by antigen-binding. In addition, we clarified that the ratio between the antigen-binding and non-binding conditions in the observed structural fluctuations is extremely relative to the binding-affinity or the Gibbs free energy change. These results indicate that the phenomena of antigen-antibody interactions considered stable states can be defined as the results of dynamical processes at the single-molecule level. Such new quantifications from angstrom-level structural fluctuations can be applied to various biological science and biotechnologies.
https://ror.org/05sj3n476 
