Pyrophosphate is a source of phosphoryl groups for Escherichia coli protein phosphorylation

The archaeon Sulfolobus solfataricus contains a membrane-associated protein kinase activity that preferentially phosphorylates threonine residues in vitro

The extreme acidothermophilic archaeon Sulfolobus solfataricus harbors a membrane-associated protein kinase activity. Its solubilization and stabilization required detergents, suggesting that this activity resides within an integral membrane protein. The archaeal protein kinase utilized purine nucleotides as phosphoryl donors in vitro. A noticeable preference for nucleotide triphosphates over nucleotide diphosphates and for adenyl nucleotides over the corresponding guanyl ones was observed. The molecular mass of the solubilized, partially purified enzyme was estimated to be approximately 125 kDa by gel filtration chromatography. Catalytic activity resided in a polypeptide with an apparent molecular mass of approximately 67 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Challenges with several exogenous substrates revealed the protein kinase to be relatively selective. Only casein, histone H4, reduced carboxyamidomethylated and maleylated lysozyme, and a peptide modeled after myosin light chains (KKRAARATSNVFA) were phosphorylated to appreciable levels in vitro. All of the aforementioned substrates were phosphorylated on threonine residues, while histone H4 was phosphorylated on serine as well. Substitution of serine for the phosphoacceptor threonine in the myosin light chain peptide produced a noticeably inferior substrate. The protein kinase underwent autophosphorylation on threonine and was relatively insensitive to a set of known inhibitors of "eukaryotic" protein kinases.

Autophosphorylation of phosphoglucosamine mutase from Escherichia coli

Phosphoglucosamine mutase (GlmM) catalyzes the formation of glucosamine-1-phosphate from glucosamine-6-phosphate, an essential step in the pathway for UDP-N-acetylglucosamine biosynthesis in bacteria. This enzyme must be phosphorylated to be active and acts according to a ping-pong mechanism involving glucosamine-1, 6-diphosphate as an intermediate (L. Jolly, P. Ferrari, D. Blanot, J. van Heijenoort, F. Fassy, and D. Mengin-Lecreulx, Eur. J. Biochem. 262:202-210, 1999). However, the process by which the initial phosphorylation of the enzyme is achieved in vivo remains unknown. Here we show that the phosphoglucosamine mutase from Escherichia coli autophosphorylates in vitro in the presence of [(32)P]ATP. The same is observed with phosphoglucosamine mutases from other bacterial species, yeast N-acetylglucosamine-phosphate mutase, and rabbit muscle phosphoglucomutase. Labeling of the E. coli GlmM enzyme with [(32)P]ATP requires the presence of a divalent cation, and the label is subsequently lost when the enzyme is incubated with either of its substrates. Analysis of enzyme phosphorylation by high-pressure liquid chromatography and coupled mass spectrometry confirms that only one phosphate has been covalently linked to the enzyme. Only phosphoserine could be detected after acid hydrolysis of the labeled protein, and site-directed mutagenesis of serine residues located in or near the active site identifies the serine residue at position 102 as the site of autophosphorylation of E. coli GlmM.

Post-translational modification of proteins by reversible phosphorylation in prokaryotes

Microorganisms have developed three different systems for catalyzing protein phosphorylation and using this reversible modificaiton to regulate their cellular activities. The first 'classical' system utilizes nucleoside-triphosphates as phosphoryl donors and leads to the modification of protein substrates at serine/threonine or tyrosine residues. The second system, called 'two-component system', requires first a sensor kinase which autophosphorylates at a histidine residue at the expense of adenosine-triphosphate, then a response regulator which is modified in turn at an aspartate residue and thereafter induces a metabolic change within the cell. The third system, called 'PTS system', makes use of phosphoenol pyruvate to generate a phosphoryl group which is passed down a chain of several proteins and finally transferred to a sugar. There is increasing evidence that, contrary to an early concept, these systems and the corresponding enzymes (protein kinases and phosphoprotein phosphatases) share a number of structural and functional similarities with the phosphorylation-dephosphorylation machineries found in eukaryotes. Therefore one can expect that microorganisms will serve, once again, as a basic model for exploring and understanding a key regulatory mechanism, reversible protein phosphorylation, which concerns all organisms.