Fig. 7.

A) Overlay of the ¹H–¹⁵N HSQC spectra of DR_0079 in the absence (black) and presence (red) of ~4:1 molar ratio of TMP-CP:DR_0079. The chemical shifts of backbone amide resonances that disappear or shift (underlined) upon the addition of TMP-CP are labeled. Spectra were collected at a ¹H resonance frequency of 600 MHz, 25°C, in buffer containing 100 mM KCl, 100 mM MgCl₂, 20 mM potassium phosphate, 2 mM DTT, pH 7.1. B + C) Residues of backbone amides that disappear (dark blue) or shift slightly (light blue) upon the addition of TMP-CP to DR_0079 at a substrate:protein molar ratio of ~4.0:1.0 are mapped unto the structure of DR_0079 and shown in two orientations that differ by ~180°. Also highlighted are E85 and E89 (orange), the residues that most likely bind the divalent cation, and G70 (magenta), the residue the cation may sit over.