Figure 6. Interaction between HasS_CTD and the signaling domain probed by NMR and fluorescence.

(A) Change of the fluorescence emission spectra of HasS_CTD upon titration with the signaling domain (solid red lines) and control spectra for HasS_CTD dilution with the buffer (dashed blue lines). Figure in the inset presents the ratio of the fluorescence intensity (at 350 nm) of HasS_CTD in complex and HasS_CTD alone, plotted versus the signaling domain concentration. (B) ¹H-¹⁵N HSQC spectra of HasS_CTD alone (blue) and in the presence of unlabeled signaling domain (red). Some of the most affected residues are pointed out and resonances of tryptophan side chain are shown in the inset. The concentrations of HasS_CTD and the HasR signaling domain were 250 µM and 800 µM, respectively. (C) Ratio of the peak intensity of two ¹⁵N-¹H HSQC spectra of ¹⁵N labeled HasS_CTD (in the presence and absence of the unlabeled signaling domain).