Conformational exchange of the Zα domain of human RNA editing enzyme ADAR1 studied by NMR spectroscopy

Z-DNA binding proteins (ZBPs) play important roles in RNA editing, innate immune responses, and viral infections. Numerous studies have implicated a role for conformational motions during ZBPs binding upon DNA, but the quantitative intrinsic conformational exchanges of ZBP have not been elucidated. To understand the correlation between the biological function and dynamic feature of the Zα domains of human ADAR1 (hZα_ADAR1), we have performed the ¹⁵N backbone amide Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments on the free hZα_ADAR1 at two different magnetic fields at 35 °C. The robust inter-dependence of parameters in the global fitting process using multi-magnetic field CPMG profiles allows us characterizing the dynamic properties of conformational changes in hZα_ADAR1. This study found that free hZα_ADAR1 exhibited the conformational exchange with a k_ex of 5784 s^-1 between the states "A" (89% population) and "B" (11% population). The different hydrophobic interactions among helices α1, α2, and α3 between these two states might correlate with efficient Z-DNA binding achieved by the hydrogen bonding interactions between its side-chains and the phosphate backbone of Z-DNA.