Binding of transcriptional activators to sigma 54 in the presence of the transition state analog ADP-aluminum fluoride: insights into activator mechanochemical action

Abstract

Conformational changes in sigma 54(σ54) and σ54-holoenzyme depend on nucleotide hydrolysis by an activator. We now show that σ54 and its holoenzyme bind to the central ATP-hydrolyzing domains of the transcriptional activators PspF and NifA in the presence of ADP–aluminum fluoride, an analog of ATP in the transition state for hydrolysis. Direct binding of σ54 Region I to activator in the presence of ADP–aluminum fluoride was shown and inferred from in vivo suppression genetics. Energy transduction appears to occur through activator contacts to σ54 Region I. ADP–aluminum fluoride-dependent interactions and consideration of other AAA+ proteins provide insight into activator mechanochemical action.