A novel class of molecular chaperones co-ordinates the assembly and targeting of complex metalloproteins by binding to an amino-terminal peptide of the cognate substrate. We have previously shown that the NarJ chaperone interacts with the N-terminus of the NarG subunit coming from the nitrate reductase complex, NarGHI. In the present study, NMR structural analysis revealed that the NarG(1–15) peptide adopts an α-helical conformation in solution. Moreover, NarJ recognizes and binds the helical NarG(1–15) peptide mostly via hydrophobic interactions as deduced from isothermal titration calorimetry analysis. NMR and differential scanning calorimetry analysis revealed a modification of NarJ conformation during complex formation with the NarG(1–15) peptide. Isothermal titration calorimetry and BIAcore experiments support a model whereby the protonated state of the chaperone controls the time dependence of peptide interaction.
Structured digital abstract