title: The Escherichia coli signal transducers PII (GlnB) and GlnK form heterotrimers in vivo: fine tuning the nitrogen signal cascade.
abstract: The PII protein is Escherichia coli's cognate transducer of the nitrogen signal to the NRII (NtrB)/NRI (NtrC) two-component system and to adenylyltransferase. Through these two routes, PII regulates both amount and activity of glutamine synthetase. GlnK is the recently discovered paralogue of PII, with a similar trimeric x-ray structure. Here we show that PII and GlnK form heterotrimers, in E. coli grown in nitrogen-poor medium. In vitro, fully uridylylated heterotrimers of the two proteins stimulated the deadenylylation activity of adenylyltransferase, albeit to a lower extent than homotrimeric PII-UMP. Fully uridylylated GlnK did not stimulate, or hardly stimulated, the deadenylylation activity. We propose that uridylylated PII/GlnK heterotrimers fine-regulate the activation of glutamine synthetase. The PII/GlnK couple is a first example of prokaryotic signal transducer that can form heterotrimers. Advantages of hetero-oligomer formation as molecular mechanism for fine-regulation of signal transduction are discussed.
authors.affiliation: Department of Biochemistry and Molecular Biology, James Cook University, Townsville, Queensland 4811, Australia.
authors.forename: W C
authors.initials: WC
authors.lastname: van Heeswijk
authors.forename: D
authors.initials: D
authors.lastname: Wen
authors.forename: P
authors.initials: P
authors.lastname: Clancy
authors.forename: R
authors.initials: R
authors.lastname: Jaggi
authors.forename: D L
authors.initials: DL
authors.lastname: Ollis
authors.forename: H V
authors.initials: HV
authors.lastname: Westerhoff
authors.forename: S G
authors.initials: SG
authors.lastname: Vasudevan
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001704:Biopolymers; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D009876:Operon; D051922:PII Nitrogen Regulatory Proteins; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; D001704:Biopolymers; D002352:Carrier Proteins; C113488:GlnK protein, Azorhizobium caulinodans; D051922:PII Nitrogen Regulatory Proteins; C404143:PIID regulatory protein, Bacteria; D009584:Nitrogen