DNA binding mechanism revealed by high resolution crystal structure of Arabidopsis thaliana WRKY1 protein

WRKY proteins, defined by the conserved WRKYGQK sequence, are comprised of a large superfamily of transcription factors identified specifically from the plant kingdom. This superfamily plays important roles in plant disease resistance, abiotic stress, senescence as well as in some developmental processes. In this study, the Arabidopsis WRKY1 was shown to be involved in the salicylic acid signaling pathway and partially dependent on NPR1; a C-terminal domain of WRKY1, AtWRKY1-C, was constructed for structural studies. Previous investigations showed that DNA binding of the WRKY proteins was localized at the WRKY domains and these domains may define novel zinc-binding motifs. The crystal structure of the AtWRKY1-C determined at 1.6 angstrom resolution has revealed that this domain is composed of a globular structure with five beta strands, forming an antiparallel beta-sheet. A novel zinc-binding site is situated at one end of the beta-sheet, between strands beta 4 and beta 5. Based on this high-resolution crystal structure and site-directed mutagenesis, we have defined and confirmed that the DNA-binding residues of AtWRKY1-C are located at beta 2 and beta 3 strands. These results provided us with structural information to understand the mechanism of transcriptional control and signal transduction events of the WRKY proteins.