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The Crp regulator of Pseudomonas putida : evidence of an unusually high affinity for its physiological effector, cAMP
Author(s) -
ArceRodríguez Alejandro,
DuranteRodríguez Gonzalo,
Platero Raúl,
Krell Tino,
Calles Belén,
de Lorenzo Víctor
Publication year - 2012
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/j.1462-2920.2011.02622.x
Subject(s) - pseudomonas putida , biology , effector , biochemistry , isothermal titration calorimetry , regulator , camp receptor protein , escherichia coli , sigma factor , promoter , rna polymerase , microbiology and biotechnology , gene , gene expression
Summary Although the genome of Pseudomonas putida KT2440 encodes an orthologue of the crp gene of Escherichia coli (encoding the cAMP receptor protein), the regulatory scope of this factor seems to be predominantly co‐opted in this bacterium for controlling non‐metabolic functions. In order to investigate the reasons for such a functional divergence in otherwise nearly identical proteins, the Crp regulator of P. putida (Crp P. putida ) was purified to apparent homogeneity and subject to a battery of in vitro assays aimed at determining its principal physicochemical properties. Analytical ultracentrifugation indicated effector‐free Crp P. putida to be a dimer in solution that undergoes a significant change in its hydrodynamic shape in the presence of cAMP. Such a conformational transition was confirmed by limited proteolysis of the protein in the absence or presence of the inducer. Thermodynamic parameters calculated by isothermal titration calorimetry revealed a tight cAMP–Crp P. putida association with an apparent K D of 22.5 ± 2.8 nM, i.e. much greater affinity than that reported for the E. coli 's counterpart. The regulator also bound cGMP, but with a K D = 2.6 ± 0.3 µM. An in vitro transcription system was then set up with purified P. putida 's RNA polymerase for examining the preservation of the correct protein–protein architecture that makes Crp to activate target promoters. These results, along with cognate gel retardation assays indicated that all basic features of the reference Crp E. coli protein are kept in the P. putida 's counterpart, albeit operating under a different set of parameters, the extraordinarily high affinity for cAMP being the most noticeable.