Atomic force spectroscopic and SPR kinetic analysis of long circular and short ssDNA molecules interacting with single-stranded DNA-binding protein

Abstract

Regulation of cellular processes and biochemical pathways would not be possible without formation of specific non-covalent complexes between nucleic acids and proteins. Single-stranded DNA-binding proteins have a high affinity for ssDNA and this interaction plays a crucial role in the control of DNA replication, recombination, transcription, translation, and repair. Characterization of the DNA–protein interactions would improve the information about abnormal cells and provide a better understanding of tumor growth, its prevention, and medical treatment. The interaction between the ssDNA-binding protein from E. coli with two ssDNA molecules (either M13mp18, 7249 bases, or a short 10 base oligonucleotide) was analyzed using atomic force microscopy providing images of the formed complexes on mica. The corresponding binding forces were determined using force spectroscopy using cantilever tips modified with ssDNA. The interactions were also characterized using the surface plasmon resonance (Biacore) providing reference data on kinetics in real time. The data from different methods were critically evaluated and discussed with respect to correlation of the single- (force spectroscopy) and multi-molecular (biosensor kinetics) results.