Practice question

Catabolite activator protein exists in equilibrium between inactive and active conformations controlled by small molecule ligand binding allosterically. Each protomer of the homodimer contains N-terminal cyclic-nucleotide-binding domain that specifically accommodates cyclic AMP in anti conformation. cAMP binding triggers hinge repositioning and ordering of C-terminal helix-turn-helix DNA recognition motif able to bind consensus TGTGA-N6-TCACA half sites with high affinity. Resulting CRP-cAMP-DNA ternary complex bends DNA and activates transcription initiation. ATP and GTP do not serve as allosteric effectors for this protein, glucose actually lowers cAMP indirectly via PTS-mediated regulation of adenylate cyclase enzymatic activity controlling synthesis.