The Effect of Ser 128 Substitution on the Structure and Stability of cAMP Receptor Protein from Escherichia coli

Kinetic measurements of denaturation and renaturation of two mutants of cAMP receptor protein (CRP) at position 128, namely Ser→Ala and Ser→Pro, were performed in order to assess changes introduced by the mutation in the quaternary structure and protein stability. No significant changes were found in the unfolding/refolding reactions. However, small perturbations in the dissociation of CRP dimer can be seen, which indicate that subunit interactions are influenced by the mutation. Studies of intrinsic fluorescence quenching of these two mutants are also reported, showing changes compared with wild-type protein. Near-UV circular dichroism measurements indicate, however, that Trp residues remain in the same environment as in the wild-type CRP. It is proposed that Ser at position 128 is involved in maintaining the proper domain alignment within CRP subunits.