The ATP hydrolyzing transcription activator phage shock protein F of Escherichia coli: Identifying a surface that binds σ⁵⁴

Abstract

Members of the protein family called ATPases associated with various cellular activities (AAA⁺) play a crucial role in transforming chemical energy into biological events. AAA⁺ proteins are complex molecular machines and typically form ring-shaped oligomeric complexes that are crucial for ATPase activity and mechanism of action. The Escherichia coli transcription activator phage shock protein F (PspF) is an AAA⁺ mechanochemical enzyme that functions to sense and relay the energy derived from nucleoside triphosphate hydrolysis to catalyze transcription by the σ⁵⁴-RNA polymerase. Closed promoter complexes formed by the σ⁵⁴-RNA polymerase are substrates for the action of PspF. By using a protein fragmentation approach, we identify here at least one σ⁵⁴-binding surface in the PspF AAA⁺ domain. Results suggest that ATP hydrolysis by PspF is coupled to the exposure of at least one σ⁵⁴-binding surface. This nucleotide hydrolysis-dependent presentation of a substrate binding surface can explain why complexes that form between σ⁵⁴ and PspF are transient and could be part of a mechanism used generally by other AAA⁺ proteins to regulate activity.