cAMP receptor protein (CRP)-mediated resistance/tolerance in bacteria: mechanism and utilization in biotechnology

Cyclic AMP receptor protein (CRP) is one of the seven global regulators in Escherichia coli, which regulates the expression of over 490 genes. It contains a cAMP binding N-terminal domain and a DNA binding C-terminal domain, connected via a short hinge region. Various stress-tolerant E. coli mutants had been obtained through transcriptional engineering of CRP. This review aims to shed some light on the possible mechanism behind these CRP variants, from the change in CRP structure, transcription profile, and DNA binding affinity. The amino acid substitutions are distributed along the protein-certain mutations have shown higher frequency than others, such as T127N and D138Y. β-Galactosidase reporter gene assay revealed that CRP mutants had lower binding affinity with all three classes of CRP-dependent promoters as compared to native CRP, which probably would change cellular transcription profile. Different CRP mutants would induce different cellular transcription profile in E. coli, but there are common genes differentially expressed in these variants, including upregulated gadAB and downregulated nontransporter genes aspA and tnaA, and transporter/poringenes malE, mglB, cstA, and lamB. We believe that transcriptional engineering of CRP can provide an alternative strain engineering method for E. coli and its detailed mechanism may need further investigations.