Phosphorylation in halobacterial signal transduction.

Abstract

Regulated phosphorylation of proteins has been shown to be a hallmark of signal transduction mechanisms in both Eubacteria and Eukarya. Here we demonstrate that phosphorylation and dephosphorylation are also the underlying mechanism of chemo‐ and phototactic signal transduction in Archaea, the third branch of the living world. Cloning and sequencing of the region upstream of the cheA gene, known to be required for chemo‐ and phototaxis in Halobacterium salinarium, has identified cheY and cheB analogs which appear to form part of an operon which also includes cheA and the following open reading frame of 585 nucleotides. The CheY and CheB proteins have 31.3 and 37.5% sequence identity compared with the known signal transduction proteins CheY and CheB from Escherichia coli, respectively. The biochemical activities of both CheA and CheY were investigated following their expression in E.coli, isolation and renaturation. Wild‐type CheA could be phosphorylated in a time‐dependent manner in the presence of [gamma‐32P]ATP and Mg2+, whereas the mutant CheA(H44Q) remained unlabeled. Phosphorylated CheA was dephosphorylated rapidly by the addition of wild‐type CheY. The mutant CheY(D53A) had no effect on phosphorylated CheA. The mechanism of chemo‐ and phototactic signal transduction in the Archaeon H.salinarium, therefore, is similar to the two‐component signaling system known from chemotaxis in the eubacterium E.coli.

Posttranslational Protein Modification inArchaea

“…Protein phosphorylation as part of an archaeal two-component signal transduction pathway was first shown for Halobacterium salinarum (373,374). In Bacteria and a very limited number of Eucarya, two-component signal transduction response pathways are responsible for the appropriate response of the cell to a wide range of environmental conditions (234,332,423).…”

“…Transduction of the ligand binding event to sensor and response regulator proteins is achieved via a cascade of phosphorylation reactions. Hence, the detection of phosphorylated Halobacterium salinarum CheA and CheY, well-characterized sensor and response regulator proteins, respectively (114,423), pointed to the presence of a two-component system in Archaea, charged with responding to various chemotactic and photactic stimuli (373,374).…”

“…The first example of an archaeal histidine kinase as part of a two-component system identified was Halobacterium salinarum CheA (373). A recombinant version of the haloarchaeal CheA histidine kinase was autophosphorylated upon addition of radiolabeled ATP and was subsequently able to transfer its phosphoryl group to an Asp residue of the Halobacterium salinarum CheY response regulator (374).…”

Transcriptional regulation of the Enterococcus faecium BM4147 vancomycin resistance gene cluster by the VanS-VanR two-component regulatory system in Escherichia coli K-12

“…Twocomponent regulatory systems are signal transduction pathways commonly used by prokaryotes to sense and adapt to stimuli in the environment; as many as 50 different ones may exist in a single bacterium such as Escherichia coli (29). Analogous signal transduction pathways have recently been identified in both eucaryotes (38) and archaea (32). These systems are characterized by a sensor histidine kinase (often a transmembrane signaling kinase such as VanS) that undergoes autophosphorylation on a conserved histidine residue.…”

The Membrane-Associated Protein-Serine/Threonine Kinase fromSulfolobus solfataricusIs a Glycoprotein

“…Many archaea also contain open reading frames potentially encoding homologs of two-component histidine kinases (11,12), variants of which act as protein-serine/threonine/tyrosine kinases in members of the Eucarya (9) and Bacteria (17,27,38,40). However, with the exception of a CheA-like two-component histidine kinase from Halobacterium salinarum (23), it has yet to be determined whether any of these deduced archaeal protein kinases possesses the catalytic properties suggested by homology searches.…”