Catabolite Activator Protein (CAP; also known as cAMP receptor protein, CRP) is a transcriptional activator that exists as a homodimer in solution, with each subunit comprising a ligand-binding domain at the N-terminus (CAPN, residues 1-138), which is also responsible for the dimerization of the protein, and a DNA-binding domain at the C-terminus (DBD, residues 139-209).