Communications between the high-affinity cyclic nucleotide binding sites in E. coli cyclic AMP receptor protein: Effect of single site mutations

Shwu Hwa Lin, James Lee

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

The binding of adenosine 3′,5′-cyclic monophosphate (cAMP) and its nonfunctional analogue, guanosine 3′,5′-cyclic monophosphate (cGMP), to the adenosine 3′,5′-cyclic monophosphate receptor protein (CRP) from Escherichia coli was investigated by means of fluorescence and isothermal titration calorimetry (ITC) at pH 7.8 and 25°C. A biphasic fluorescence titration curve was observed, confirming the previous observation reported by this laboratory (Heyduk and Lee (1989) Biochemistry 28, 6914-6924). However, the triphasic titration curve obtained from the ITC study suggests that the cAMP binding to CRP is more complicated than the previous conclusion that CRP binds sequentially two molecules of cAMP with negative cooperativity. The binding data can best be represented by a model for two identical interactive high-affinity sites and one low-affinity binding site. Unlike cAMP, the binding of cGMP to CRP exhibits no cooperativity between the high-affinity sites. The effects of mutations on the bindings of cAMP and cGMP to CRP were also investigated. The eight CRP mutants studied were K52N, D53H, S62F, T127L, G141Q, L148R, H159L, and K52N/H159L. These sites are located neither in the ligand binding site nor at the subunit interface. The binding was monitored by fluorescence. Although these mutations are at a variety of locations in CRP, the basic mechanism of CRP binding to cyclic nucleotides has not been affected. Two cyclic nucleotide molecules bind to the high-affinity sites of CRP. The cooperativity of cAMP binding is affected by mutation. It ranges from negative to positive cooperativity. The binding of cGMP shows none. With the exception of the T127L mutant, the free energy change for DNA-CRP complex formation increases linearly with increasing free energy change associated with the cooperativity of cAMP binding. This linear relationship implies that the protein molecule modulates the signal in the binding of cAMP, even though the mutation is not directly involved in cAMP or DNA binding. In addition, the significant differences in the amplitude of fluorescent signal indicate that the mutations also affect the surface characteristics of CRP. These results imply that these mutations are not perturbing specific pathways of signal transmission. Instead, these results are more consistent with the concept that CRP exists as an ensemble of native states, the distribution of which can be altered by these mutations.

Original languageEnglish (US)
Pages (from-to)11857-11867
Number of pages11
JournalBiochemistry
Volume41
Issue number39
DOIs
StatePublished - Oct 1 2002

Fingerprint

Cyclic Nucleotides
Binding Sites
Mutation
Communication
Proteins
Titration
Calorimetry
Fluorescence
Adenosine
Free energy
Molecules
E coli cyclic AMP receptor protein
Biochemistry
Guanosine
Escherichia coli Proteins
DNA
Mutant Proteins
Protein Binding
Signal Transduction
Observation

ASJC Scopus subject areas

  • Biochemistry

Cite this

Communications between the high-affinity cyclic nucleotide binding sites in E. coli cyclic AMP receptor protein : Effect of single site mutations. / Lin, Shwu Hwa; Lee, James.

In: Biochemistry, Vol. 41, No. 39, 01.10.2002, p. 11857-11867.

Research output: Contribution to journalArticle

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