Crystallization and preliminary X-ray analysis of the ATPase domain of the σ⁵⁴-dependent transcription activator NtrC1 from Aquifex aeolicus bound to the ATP analog ADP–BeF_x

One way that bacteria regulate the transcription of specific genes to adapt to environmental challenges is to use different σ factors that direct the RNA polymerase holoenzyme to distinct promoters. Unlike σ⁷⁰ RNA polymerase (RNAP), σ⁵⁴ RNAP is unable to initiate transcription without an activator: enhancer-binding protein (EBP). All EBPs contain one ATPase domain that belongs to the family of ATPases associated with various cellular activities (AAA+ ATPases). AAA+ ATPases use the energy of ATP hydrolysis to remodel different target macromolecules to perform distinct functions. These mechanochemical enzymes are known to form ring-shaped oligomers whose conformations strongly depend upon nucleotide status. Here, the crystallization of the AAA+ ATPase domain of an EBP from Aquifex aeolicus, NtrC1, in the presence of the non-hydrolyzable ATP analog ADP–BeF_x is reported. X-ray diffraction data were collected from two crystals from two different protein fractions of the NtrC1 ATPase domain. Previously, this domain was co-crystallized with ADP and ATP, but the latter crystals were grown from the Walker B substitution variant E239A. Therefore, the new data sets are the first for a wild-type EBP ATPase domain co-crystallized with an ATP analog and they reveal a new crystal form. The resulting structure(s) will shed light on the mechanism of EBP-type transcription activators.