Characterization of the Elk-1 ETS DNA-binding domain

The ETS domain family of transcription factors is comprised of several important proteins that are involved in controlling key cellular events such as proliferation, differentiation, and development. One such protein, Elk-1, regulates the activity of the c-fos promoter in response to extracellular stimuli. Elk-1 is representative of a subgroup of ETS domain proteins that utilize a bipartite recognition mechanism that is mediated by both protein- DNA and protein-protein interactions. In this study, we have overexpressed, purified, and characterized the ETS DNA-binding domain of Elk-1 (Elk-93). Elk-93 was expressed in Escherichia coli as a fusion protein with glutathione S-transferase and purified to homogeneity from both the soluble and insoluble fractions using a two-column protocol. A combination of CD, NMR, and fluorescence spectroscopy demonstrates that Elk-93 represents an independently folded domain of mixed α/β structure in which the three conserved tryptophans appear to contribute to the hydrophobic core of the protein. Moreover, DNA binding studies demonstrate that Elk-93 binds DNA with both high affinity (K(d) ≃ 0.85 x 10-10 M) and specificity. Circular permutation analysis indicates that DNA binding by Elk-93 does not induce significant bending of the DNA. Our results are discussed with respect to predictive models for the structure of the ETS DNA-binding domain.