The structural basis for regulated assembly and function of the transcriptional activator NtrC

Abstract

In two-component signal transduction, an input triggers phosphorylation of receiver domains that regulate the status of output modules. One such module is the AAA+ ATPase domain in bacterial enhancer-binding proteins that remodel the σ54 form of RNA polymerase. We report X-ray solution scattering and electron microscopy structures of the activated, full-length nitrogen-regulatory protein C (NtrC) showing a novel mechanism for regulation of AAA+ ATPase assembly via the juxtaposition of the receiver domains and ATPase ring. Accompanying the hydrolysis cycle that is required for transcriptional activation, we observed major order–disorder changes in the GAFTGA loops involved in σ54 binding, as well as in the DNA-binding domains.