Negative control in two-component signal transduction by transmitter phosphatase activity

Food Science Graduate Group Department of Microbiology, University of California, Davis, California, USA.
Molecular Microbiology (Impact Factor: 4.42). 09/2011; 82(2):275-86. DOI: 10.1111/j.1365-2958.2011.07829.x
Source: PubMed


Bifunctional sensor transmitter modules of two-component systems exert both positive and negative control on the receiver domain of the cognate response regulator. In negative control, the transmitter module accelerates the rate of phospho-receiver dephosphorylation. This transmitter phosphatase reaction serves the important physiological functions of resetting response regulator phosphorylation level and suppressing cross-talk. Although the biochemical reactions underlying positive control are reasonably well understood, the mechanism for transmitter phosphatase activity has been unknown. A recent hypothesis is that the transmitter phosphatase reaction is catalysed by a conserved Gln, Asn or Thr residue, via a hydrogen bond between the amide or hydroxyl group and the nucleophilic water molecule in acyl-phosphate hydrolysis. This hypothetical mechanism closely resembles the established mechanisms of auxiliary phosphatases such as CheZ and CheX, and may be widely conserved in two-component signal transduction. In addition to the proposed catalytic residues, transmitter phosphatase activity also requires the correct transmitter conformation and appropriate interactions with the receiver. Evidence suggests that the phosphatase-competent and autokinase-competent states are mutually exclusive, and the corresponding negative and positive activities are likely to be reciprocally regulated through dynamic control of transmitter conformations.

Full-text preview

Available from:
    • "In some sensor kinases it has been shown that within a conserved E/DxxT motif of the DHp domain, the Thr residue is critical for phosphatase activity (Huynh & Stewart, 2011; Willett & Kirby, 2012). FeuQ shares this conserved motif, but mutations to the conserved Thr did not give a phenotype consistent with eliminated phosphatase activity (data not shown). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Two-component signaling systems allow bacteria to recognize and respond to diverse environmental stimuli. Auxiliary proteins can provide an additional layer of control to these systems. The Sinorhizobium meliloti FeuPQ two-component system is required for symbiotic development and is negatively regulated by the auxiliary small periplasmic protein FeuN. This study explores the mechanistic basis of this regulation. We provide evidence that FeuN directly interacts with the sensor kinase FeuQ. The isolation and characterization of an extensive set of FeuN-insensitive and FeuN-mimicking variants of FeuQ reveal specific FeuQ residues (periplasmic and intracellular) that control the transmission of FeuN-specific signaling information. Similar analysis of the FeuN protein highlights short patches of compatibly charged residues on each protein that likely engage one another, giving rise to the downstream effects on target gene expression. The accumulated evidence suggests that the periplasmic interaction between FeuN and FeuQ introduces an intracellular conformational change in FeuQ, resulting in an increase in its ability to remove phosphate from its cognate response regulator FeuP. These observations underscore the complex manner in which membrane-spanning sensor kinases interface with the extracytoplasmic environment and convert that information to changes in intracellular processes.
    No preview · Article · Dec 2014 · Microbiology
  • Source
    • "Detection of WalR~P amounts in pneumococcal cells 647 the strong dependence of the phosphatase activity on Mg 2+ ion (Zhu et al., 2000; Gutu et al., 2010; Huynh and Stewart, 2011). WalK with the T225A, S217A or R221K amino acid changes (Fig. S3C, D and H) showed similar low-level accumulation of WalR~P as wild-type WalK + in Mg 2+ buffer and were not ostensibly defective in phosphatase or other WalK activities. "
    [Show abstract] [Hide abstract]
    ABSTRACT: WalRK (YycFG) two-component systems (TCSs) of low-GC Gram-positive bacteria play critical roles in regulating peptidogylcan hydrolase genes involved in cell division and wall stress responses. The WalRK (VicRK) TCSs of Streptococcus pneumoniae (pneumococcus) and other Streptococcus species show numerous differences with those of other low-GC species. Notably, the pneumococcal WalK sensor kinase is not essential for normal growth in culture, unlike its homologues in Bacillus and Staphylococcus species. The WalK sensor kinase possesses histidine autokinase activity and mediates dephosphorylation of phosphorylated WalR∼P response regulator. To understand the contributions of these two WalK activities to pneumococcal growth, we constructed and characterized a set of walK kinase and phosphatase mutants in biochemical reactions and in cells. We identified an amino acid substitution in WalK that significantly reduces phosphatase activity, but not other activities. Comparisons were made between WalRK regulon expression levels and WalR∼P amounts in cells determined by Phos-tag SDS-PAGE. Reduction of WalK phosphatase activity resulted in nearly 90% phosphorylation to WalR∼P, consistent with the conclusion that WalK phosphatase is strongly active in exponentially growing cells. WalK phosphatase activity was also shown to depend on the WalK PAS domain and to limit cross-talk and the recovery of WalR∼P from walK(+) cells.
    Full-text · Article · Sep 2012 · Molecular Microbiology
  • Source
    • "These pathways, a primary means of signal transduction in prokaryotes, typically involve a sensor histidine kinase that, upon receipt of an input stimulus, autophosphorylates and then transfers its phosphoryl group to a cognate response regulator, which in turn modulates gene expression (Stock et al., 2000). Most histidine kinases are bifunctional and can, in the absence of an input signal, stimulate the dephosphorylation of their cognate response regulators, effectively acting as phosphatases (Huynh and Stewart, 2011). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Orthologous proteins often harbor numerous substitutions, but whether these differences result from neutral or adaptive processes is usually unclear. To tackle this challenge, we examined the divergent evolution of a model bacterial signaling pathway comprising the kinase PhoR and its cognate substrate PhoB. We show that the specificity-determining residues of these proteins are typically under purifying selection but have, in α-proteobacteria, undergone a burst of diversification followed by extended stasis. By reversing mutations that accumulated in an α-proteobacterial PhoR, we demonstrate that these substitutions were adaptive, enabling PhoR to avoid crosstalk with a paralogous pathway that arose specifically in α-proteobacteria. Our findings demonstrate that duplication and the subsequent need to avoid crosstalk strongly influence signaling protein evolution. These results provide a concrete example of how system-wide insulation can be achieved postduplication through a surprisingly limited number of mutations. Our work may help explain the apparent ease with which paralogous protein families expanded in all organisms.
    Full-text · Article · Jul 2012 · Cell
Show more