Crystallization and preliminary X-ray crystallographic studies of the Z-DNA-binding domain of a PKR-like kinase (PKZ) in complex with Z-DNA.

PKZ, a PKR-like eIF2alpha kinase, consists of a Z-DNA-specific binding domain (Zalpha) and an eIF2alpha kinase domain. The kinase activity of PKZ is modulated by the binding of Zalpha to Z-DNA. The mechanisms underlying Z-DNA binding and the subsequent stimulation of PKZ raise intriguing questions. Interestingly, the Z-DNA-binding domain of PKZ from goldfish (Carassius auratus; caZalpha(PKZ)) shows limited sequence homology to other canonical Zalpha domains, suggesting that it may have a distinct Z-DNA-recognition mode. In this study, the Z-DNA-binding activity and stoichiometry of caZalpha(PKZ) were confirmed using circular dichroism (CD). In addition, preliminary X-ray studies of the caZalpha(PKZ)-Z-DNA complex are reported as the first step in the determination of its three-dimensional structure. Bacterially expressed recombinant caZalpha(PKZ) was purified and crystallized with Z-DNA at 295 K using the microbatch method. X-ray diffraction data were collected to 1.7 A resolution with an R(merge) of 7.4%. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 55.54, b = 49.93, c = 29.44 A, beta = 96.5 degrees . Structural analysis of caZalpha(PKZ)-Z-DNA will reveal the binding mode of caZalpha(PKZ) to Z-DNA and its relevance to other Z-DNA-binding proteins.