Revisiting the mechanism of activation of cyclic AMP receptor protein (CRP) by cAMP in Escherichia coli: Lessons from a subunit-crosslinked form of CRP

Abstract

Cyclic AMP receptor protein (CRP), the global transcription regulator in prokaryotes, is active only as a cAMP–CRP complex. Binding of cAMP changes the conformation of CRP, transforming it from a transcriptionally ‘inactive’ to an ‘active’ molecule. These conformers are also characterized by distinct biochemical properties including the ability to form an S–S crosslink between the C178 residues of its two monomeric subunits. We studied a CRP variant (CRPcl), in which the subunits are crosslinked. We demonstrate that CRPcl can activate transcription even in the absence of cAMP. Implications of these results for the crystallographically-determined structure of cAMP–CRP are discussed.