SPR sensorgrams of the binding of TcaR to DNA fragments at 25°C.

(A) SPR sensorgram of the binding of varying concentrations of TcaR (4, 8, 16, 32, 64 nM) to biotin-labeled GC33 ssDNA (33mer GC-rich single-stranded DNA fragment) captured on SA chip with a ligand density of 120RU. The increase in RUs from the baseline was measured and used to calculated k_a and k_d. One RU represents the binding of approximately 1 pg protein/mm². (B) Comparison of SPR derived binding curves for different types of immobilized biotin-labeled DNA fragments interacting with TcaR protein (64 nM). The sensograms represent binding of, from bottom to top: GC8, GC17, IcaR DNA1, AT33 and GC33. The association (k_a) and dissociation rate constants (k_d) were derived by fitting the sensograms to a Langumir binding rate equations and are tabulated in Table 1. (C) The SPR sensorgram of the binding of different DNA binding proteins to the immobilized GC33 ssDNA fragment. The concentration of each target protein is 64 nM, followed by the same condition as used in other Biacore assays. (D) Sensorgram of the interaction between the immobilized GC33 ssDNA fragment and the TcaR protein (64 nM) in the presence of 640 nM kanamycin or ampicillin.