Heterotrimerization of PII-like signalling proteins: implications for PII-mediated signal transduction systems.
PII-like signalling molecules are trimeric proteins composed of 12-13 kDa polypeptides encoded by the glnB gene family. Heterologous expression of a cyanobacterial glnB gene in Escherichia coli leads to an inactivation of E. coli's own PII signalling system. In the present work, we show that this effect is caused by the formation of functionally inactive heterotrimers between the cyanobacterial glnB gene product and the E. coli PII paralogues GlnB and GlnK. This led to the discovery that GlnK and GlnB of E. coli also form heterotrimers with each other. The influence of the oligomerization partner on the function of the single subunit was studied using heterotrimerization with the Synechococcus PII protein. Uridylylation of GlnB and GlnK was less efficient but still possible within these heterotrimers. In contrast, the ability of GlnB-UMP to stimulate the adenylyl-removing activity of GlnE (glutamine synthetase adenylyltransferase/removase) was almost completely abolished, confirming that rapid deadenylylation of glutamine synthetase upon nitrogen stepdown requires functional homotrimeric GlnB protein. Remarkably, however, rapid adenylylation of glutamine synthetase upon exposing nitrogen-starved cells to ammonium was shown to occur in the absence of a functional GlnB/GlnK signalling system as efficiently as in its presence.
Lehrstuhl für Mikrobiologie der Universität München, Maria-Ward-Str. 1a, D-80638 München, Germany. Karl.Forchhammer@mikro.bio.uni-giessen.de
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D000249:Adenosine Monophosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D000458:Cyanobacteria; D004926:Escherichia coli; D005809:Genes, Regulator; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D051922:PII Nitrogen Regulatory Proteins; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011487:Protein Conformation; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014542:Uridine Monophosphate / Q000378:metabolism
D001426:Bacterial Proteins; D002352:Carrier Proteins; C113488:GlnK protein, Azorhizobium caulinodans; D051922:PII Nitrogen Regulatory Proteins; D000249:Adenosine Monophosphate; C404143:PIID regulatory protein, Bacteria; D014542:Uridine Monophosphate; D011494:Protein Kinases; C055699:protein kinase-phosphatase NTRB; D010749:Phosphoprotein Phosphatases; D005974:Glutamate-Ammonia Ligase