title: The nitrogen interaction network in Synechococcus WH5701, a cyanobacterium with two PipX and two P(II)-like proteins.
abstract: Nitrogen regulation involves the formation of different types of protein complexes between signal transducers and their transcriptional or metabolic targets. In oxygenic phototrophs, the signal integrator P(II) activates the enzyme N-acetyl-l-glutamate kinase (NAGK) by complex formation. P(II) also interacts with PipX, a protein with a tudor-like domain that mediates contacts with P(II) and with the transcriptional regulator NtcA, to which it binds to increase its activity. Here, we use a combination of in silico, yeast two-hybrid and in vitro approaches to investigate the nitrogen regulation network of Synechococcus WH5701, a marine cyanobacterium with two P(II) (GlnB_A and GlnB_B) and two PipX (PipX_I and PipX_II) proteins. Our results indicate that GlnB_A is functionally equivalent to the canonical P(II) protein from Synechococcus elongatus. GlnB_A interacted with PipX and NAGK proteins and stimulated NAGK activity, counteracting arginine inhibition. GlnB_B had only a slight stimulatory effect on NAGK activity, but its potential to bind effectors and form heterotrimers in Synechococcus WH5701 indicates additional regulatory functions. PipX_II, and less evidently PipX_I, specifically interacted with GlnB_A and NtcA, supporting a role for both Synechococcus WH5701 PipX proteins in partner swapping with GlnB_A and NtcA.
authors.affiliation: División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain.
authors.forename: Karim Boumediene
authors.initials: KB
authors.lastname: Laichoubi
authors.affiliation: Lehrstuhl für Mikrobiologie, Organismische Interaktionen, University Tuebingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Beez
authors.affiliation: División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Espinosa
authors.affiliation: Lehrstuhl für Mikrobiologie, Organismische Interaktionen, University Tuebingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany.
authors.forename: Karl
authors.initials: K
authors.lastname: Forchhammer
authors.affiliation: División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain.
authors.forename: Asunción
authors.initials: A
authors.lastname: Contreras
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D019295:Computational Biology; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D009584:Nitrogen / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D046940:Synechococcus / Q000235:genetics* / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D001426:Bacterial Proteins; D009584:Nitrogen