Surface plasmon resonance study of the molecular recognition between polymerase and DNA containing various mismatches and conformational changes of DNA-protein complexes.

Although surface plasmon resonance (SPR) biosensor technique has been used to study protein-protein interactions and to detect conformational changes of proteins, it has not been shown whether the SPR biosensor can be used to study a complex kinetic system such as the protein-DNA binding, which sometimes involves several binding steps as well as dynamic conformational changes of the complexes. In this study, we have used SPR biosensor and T7 polymerase as the model system to study the interactions of the polymerase with a series of DNA template-primer duplexes containing different number of mismatches and GC contents at various positions near the primer 3'-end. In general, the binding constants measured by the SPR are several magnitudes smaller than those determined in solution, indicating the limitation of the surface-based technique for measuring solution-based interactions. However, the distinct polymerase binding profiles obtained for DNA duplexes differed by as low as a single mismatch suggest that the SPR data can be used for relative comparison purpose among a set of experiments carried out under identical conditions. The successful fitting of the binding profiles using the established translocation model also demonstrated that SPR can be used to monitor conformational changes, as well as to derive relative kinetic values, within a complicated DNA-protein interaction system. The results also demonstrated that SPR biosensor may be used as a sensitive technique for studying molecular recognition events, such as single-base discrimination involved in protein-DNA interactions.