Signal Transmission in Escherichia coli Cyclic AMP Receptor Protein for Survival in Extreme Acidic Conditions

Abstract

During the life cycle of enteric bacterium Escherichia coli, it encounters a wide spectrum of pH changes. The asymmetric dimer of the cAMP receptor protein, CRP, plays a key role in regulating the expressions of genes and the survival of E. coli. To elucidate the pH effects on the mechanism of signal transmission, we present a combination of results derived from ITC, crystallography, and computation. CRP responds to a pH change by inducing a differential effect on the affinity for the binding events to the two cAMP molecules, ensuing in a reversible conversion between positive and negative cooperativity at high and low pH, respectively. The structures of four crystals at pH ranging from 7.8 to 6.5 show that CRP responds by inducing a differential effect on the structures of the two subunits, particularly in the DNA binding domain. Employing the COREX/BEST algorithm, computational analysis shows the change in the stability of residues at each pH. The change in residue stability alters the connectivity between residues including those in cAMP and DNA binding sites. Consequently, the differential impact on the topology of the connectivity surface among residues in adjacent subunits is the main reason for differential change in affinity; that is, the pH-induced differential change in residue stability is the biothermodynamic basis for the change in allosteric behavior. Furthermore, the structural asymmetry of this homodimer amplifies the differential impact of any perturbations. Hence, these results demonstrate that the combination of these approaches can provide insights into the underlying mechanism of an apparent complex allostery signal and transmission in CRP.

Hierarchic regulation of a metabolic pathway: H-NS, CRP, and SsrB control myo -inositol utilization by Salmonella enterica

“…In B. subtilis , even two distinct catabolite-responsive elements were found to be involved in catabolite repression of the MI degradation operon ( 42 ). CRP binding to its specific site on the target DNA is expected to generate a bandshift representative of one CRP homodimer ( 43 ) and a DNA fragment. Depending on the size of DNA molecule and location of the CRP site in the DNA molecule, multiple CRP molecules may bind the DNA molecule at additional sites as protein concentrations increase, resulting in super-shifts.…”