Allosteric regulation of the cAMP receptor protein

The cyclic AMP receptor protein (CRP) of Escherichia coli is a dimer made u p of identical subunits. Each CRP subunit contains a cyclic nucleotide bind ing pocket and the CRP dimer exhibits negative cooperativity in binding cAM P. In solutions containing cAMP, CRP undergoes sequential conformation chan ges from the inactive ape-form through the active CRP:(cAMP)(1) complex to the less active CRP:(cAMP)(2) complex depending on the cAMP concentration. Apo-CRP binds DNA with low affinity and no apparent sequence specificity. T he CRP:(cAMP)(1) complex exhibits high affinity, sequence-specific DNA bind ing and interacts with RNA polymerase. whether free in solution or complexe d with DNA. The results of genetic. biochemical and biophysical studies hav e helped to uncover many of the details of cAMP-mediated allosteric control over CRP conformation and activity as a transcription factor. These studie s indicate that cAMP binding produces only small, but significant, changes in CRP structure; changes that include subunit realignment and concerted mo tion of the secondary structure elements within the C-terminal DNA binding domain of each subunit. These adjustments promote CRP surface-patch interac tion with RNA polymerase and protrusion of the F-helix to promote CRP site- specific interaction with DNA. Interactions between CRP and RNA polymerase at CRP-dependent promoters produce active ternary transcription complexes. (C) 2001 Elsevier Science B.V. All rights reserved.