CRP is a homodimeric protein with each subunit consisting
of three domains: the N-terminal domain (residues 1–134)
is responsible for CRP dimerization and for interacting with
the allosteric effector cAMP; the C-terminal domain (residues
140–209) is responsible for interacting with DNA; and the flexible
hinge (residues 135–139) covalently couple these two domains
(Martinez-Antonio and Collado-Vides, 2003; Zhou and Yang, 2006).
Some tolerant phenotypes of E. coli have been successfully achieved
by the engineering the global regulator CRP (Table 3). Unlike
the direct evolution of enzymes in which the amino acid mutations
are always located around the active site of enzyme, the
mutations in CRP were relatively decentralized (Tables 2 and 3).