The serine, threonine, and/or tyrosine-specific protein kinases and protein phosphatases of prokaryotic organisms: a family portrait.

Inspection of the genomes for the bacteria Bacillus subtilis 168, Borrelia burgdorferi B31, Escherichia coli K-12, Haemophilus influenzae KW20, Helicobacter pylori 26695, Mycoplasma genitalium G-37, and Synechocystis sp PCC 6803 and for the archaeons Archaeoglobus fulgidus VC-16 DSM4304, Methanobacterium thermoautotrophicum delta H, and Methanococcus jannaschii DSM2661 revealed that each contains at least one ORF whose predicted product displays sequence features characteristic of eukaryote-like protein-serine/threonine/tyrosine kinases and protein-serine/threonine/tyrosine phosphatases. Orthologs for all four major protein phosphatase families (PPP, PPM, conventional PTP, and low molecular weight PTP) were present in the bacteria surveyed, but not all strains contained all types. The three archaeons surveyed lacked recognizable homologs of the PPM family of eukaryotic protein-serine/threonine phosphatases; and only two prokaryotes were found to contain ORFs for potential phosphatases from all four major families. Intriguingly, our searches revealed a potential ancestral link between the catalytic subunits of microbial arsenate reductases and the protein-tyrosine phosphatases; they share similar ligands (arsenate versus phosphate) and features of their catalytic mechanism (formation of arseno-versus phospho-cysteinyl intermediates). It appears that all prokaryotic organisms, at one time, contained the genetic information necessary to construct protein phosphorylation-dephosphorylation networks that target serine, threonine, and/or tyrosine residues on proteins. However, the potential for functional redundancy among the four protein phosphatase families has led many prokaryotic organisms to discard one, two, or three of the four.