Probing protein-protein interaction forces using single-molecule force spectroscopy

The invention of atomic force microscopy (AFM) provides new technology for measuring the molecular specific binding forces. With the use of AFM single-molecule force spectroscopy (SMFS), the CD20-rituximab binding forces were measured on purified CD20 proteins (CD20 segment protein and CD20 full-length protein) and on Burkitt´s lymphoma Raji cells, respectively. With AFM probe functionalization technology, rituximabs were linked onto AFM tips. With substrate functionalization technology, purified CD20 segment proteins and CD20 full-length proteins were attached onto mica. Lymphoma Raji cells were immobilized onto glass substrate with electrostatic adsorption and chemical fixation. The differences of measuring the binding forces on purified proteins and on cells were analyzed. The experimental results indicate that the binding force between CD20 segment protein and rituximab were markedly larger than that of CD20 full-length protein and CD20 protein on lymphoma cells, providing an effective method for investigating the rituximab´s mechanism.