Ammonium sensing in Escherichia coli. Role of the ammonium transporter AmtB and AmtB-GlnK complex formation.
The Amt proteins are high affinity ammonium transporters that are conserved in all domains of life. In bacteria and archaea the Amt structural genes (amtB) are invariably linked to glnK, which encodes a member of the P(II) signal transduction protein family, proteins that regulate many facets of nitrogen metabolism. We have now shown that Escherichia coli AmtB is inactivated by formation of a membrane-bound complex with GlnK. Complex formation is reversible and occurs within seconds in response to micromolar changes in the extracellular ammonium concentration. Regulation is mediated by the uridylylation/deuridylylation of GlnK in direct response to fluctuations in the intracellular glutamine pool. Furthermore under physiological conditions AmtB activity is required for GlnK deuridylylation. Hence the transporter is an integral part of the signal transduction cascade, and AmtB can be formally considered to act as an ammonium sensor. This system provides an exquisitely sensitive mechanism to control ammonium flux into the cell, and the conservation of glnK linkage to amtB suggests that this regulatory mechanism may occur throughout prokaryotes.
Javelle
Arnaud
A
Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, United Kingdom.
Severi
Emmanuele
E
Thornton
Jeremy
J
Merrick
Mike
M
D001692:Biological Transport; D027682:Cation Transport Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D008954:Models, Biological; D009713:Nucleotidyltransferases; D051922:PII Nitrogen Regulatory Proteins; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*
C111096:AmtB protein, E coli; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D051922:PII Nitrogen Regulatory Proteins; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; D011494:Protein Kinases; C497878:glnK protein, E coli; D009713:Nucleotidyltransferases