Effects of DNA mismatches on binding affinity and kinetics of polymerase-DNA complexes as revealed by surface plasmon resonance biosensor

In this study, surface plasmon resonance (SPR) biosensor techniques were used to obtain quantitative information on the kinetics of the DNA and polymerase I (Klenow fragment) interaction. DNA duplexes containing different base compositions at the binding site were immobilized on the SPR sensor surface via biotin-streptavidin chemistry and the subsequent binding of the polymerase was measured in real time. Various kinetic models were tested and a translocation model was shown to provide the best fit for the binding and dissociation profiles. The results revealed that the enzyme binds to DNA at both the polymerase and the exonuclease domains with different association and dissociation rates as well as affinity constants, depending on the presence of mismatches near the primer 3'-end. Introduction of unpaired bases increases the DNA binding affinity towards the exonuclease domain and promotes the translocation of DNA from the polymerase site to the exonuclease site. The results also demonstrated that SPR biosensors may be used as a sensitive technique for studying molecular recognition events such as single-base discrimination involved in protein-DNA interaction.