NMR elucidation of reduced B-Z transition activity of PKZ protein kinase at high NaCl concentration.

A Z-DNA binding protein (ZBP)-containing protein kinase (PKZ) in fish species has an important role in the innate immune response. Previous structural studies of the Zα domain of the PKZ from Carassius auratus (caZα) showed that the protein initially binds to B-DNA and induces B-Z transition of double stranded DNA in a salt concentration-dependent manner. However, the significantly reduced B-Z transition activity of caZα at high salt concentration was not fully understood. In this study, we present the binding affinity of the protein for B-DNA and Z-DNA and characterize its extremely low B-Z transition activity at 250 mM NaCl. Our results emphasize that the B-DNA-bound form of caZα can be used as molecular ruler to measure the degree of B-Z transition.